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We review mechanisms for pre-emptive acclimation in plants and propose a conceptual model linking developmental and evolutionary ecology with the acquisition of information through sensing of cues and signals. The idea is that plants acquire much of the information in the environment not from individual cues and signals but instead from their joint multivariate properties such as correlations. If molecular signalling has evolved to extract such information, the joint multivariate properties of the environment must be encoded in the genome, epigenome, and phenome. We contend that multivariate complexity explains why extrapolating from experiments done in artificial contexts into natural or agricultural systems almost never works for characters under complex environmental regulation: biased relationships among the state variables in both time and space create a mismatch between the evolutionary history reflected in the genotype and the artificial growing conditions in which the phenotype is expressed. Our model can generate testable hypotheses bridging levels of organization. We describe the model and its theoretical bases, and discuss its implications. We illustrate the hypotheses that can be derived from the model in two cases of pre-emptive acclimation based on correlations in the environment: the shade avoidance response and acclimation to drought. [ABSTRACT FROM AUTHOR]

Understanding the long-term responses of crop yield and soil organic carbon to fertilization is necessary to sustain food supply in a context of global change. The time-course of winter wheat yield and soil organic carbon were established in a 31-year long experiment with four fertilization regimes: unfertilized control; fertilized with mineral nitrogen and phosphorus, NP; fertilized with mineral N, P and K, NPK; and fertilized with manure and mineral NPK, MNPK. Over the time series, mean temperature increased at 0.054 ℃ year−1 (i.e. 1.67 degrees over the course of the experiment) and annual precipitation increased at 8.9 mm year−1. Yield did not show trends in unfertilized controls, increased at 210 kg ha−1 year−1 in the first 20 years and decreased slightly afterwards in the NP and NPK treatments, and increased at 310 kg ha−1 in the MNPK treatment until 2006, and leveled off afterwards. Soil organic carbon increased linearly with rates from 0.05 g kg−1 year−1 in unfertilized controls to 0.24 g kg−1 year−1 in MNPK. In fertilized crops, yield correlated nonlinearly with annual precipitation, and linearly with average temperature during the growing season. Across fertilizer treatments, yield correlated nonlinearly with soil organic carbon and the thresholds of soil organic carbon for peak yield increased with water supply. It is concluded that the combination of organic and inorganic fertilizers contributed to yield and soil organic carbon against the background of a warmer and wetter climate. • Application of mineral fertilizer alone cannot sustain high wheat yield over time. • Applying both organic and inorganic fertilizers maintained high wheat yield. • There was a quadratic-linear relationship between wheat yield and SOC content. • Organic manure input could be beneficial to mitigate climate change. [ABSTRACT FROM AUTHOR]

Owing to the interaction between genotype and environment (G x E), identifying traits to increase wheat yield and grain protein concentration simultaneously or increasing one without affecting the other remains a challenge. Phenotypic plasticity is an insightful perspective to understand G x E. To explore the relations of wheat yield and grain protein concentration in response to N input and its physiological basis from the perspective of phenotypic plasticity. We established a factorial experiment combining 14 winter wheat cultivars and four N fertilization rates (0, 45, 90 and 135 kg ha−1) in eight environments. We analyzed the interaction of cultivar and N combining a phenotypic plasticity framework and a three-phase model of grain yield and protein response to N input. The phases are: phase I, N supply limits both yield and grain protein; phase II, N supply limits grain protein but not yield; and phase III, N supply does not limit yield or grain protein concentration Grain yield plasticity was positively associated to yield in high-yielding environments without N limitations (phase II) with no cost in low yielding environments, and associated to harvest index. Grain protein plasticity was positively associated to protein in high protein environments without N limitations (phase III). Plasticity of grain protein concentration was negatively associated to grain number m −2, resulting in moderate negative association of protein plasticity and yield. Grain C:N ratio associated weakly and positively with yield plasticity and strongly and negatively for grain protein plasticity. This work proposes a yield-protein plasticity framework combined with a three-phase model that allows to disclose G × N interactions. Under our experimental conditions, we identified physiological mechanisms associated to yield and protein plasticity. Yield and protein plasticity can contribute guiding grower's cultivar selection towards high yield plasticity cultivars when aiming to high yield with acceptable protein levels or high protein plasticity cultivars to ensure high protein at the expense of lower yields. Yield plasticity brings opportunity to breed for high yielding cultivars while maintaining grain protein concentration. Accuracy of N recommendations models and mechanistic crop models can be improved by accounting for G × N interactions through plasticity of yield and grain protein. • We propose a yield-protein plasticity framework to assess G × N interactions. • Yield associated with yield plasticity in high yield non-N limiting environments. • Yield plasticity was unrelated with grain protein. • Protein plasticity associated negatively with yield. • Harvest index associated with yield plasticity in high yielding environments. [ABSTRACT FROM AUTHOR]

Technologies, from molecular genetics to precision agriculture, are outpacing theory, which is becoming a bottleneck for crop improvement. Here, we outline theoretical insights on the wheat phenotype from the perspective of three evolutionary and ecologically important relations—mother–offspring, plant–insect and plant–plant. The correlation between yield and grain number has been misinterpreted as cause-and-effect; an evolutionary perspective shows a striking similarity between crop and fishes. Both respond to environmental variation through offspring number; seed and egg size are conserved. The offspring of annual plants and semelparous fishes, lacking parental care, are subject to mother–offspring conflict and stabilizing selection. Labile reserve carbohydrates do not fit the current model of wheat yield; they can stabilize grain size, but involve trade-offs with root growth and grain number, and are at best neutral for yield. Shifting the focus from the carbon balance to an ecological role, we suggest that labile carbohydrates may disrupt aphid osmoregulation, and thus contribute to wheat agronomic adaptation. The tight association between high yield and low competitive ability justifies the view of crop yield as a population attribute whereby the behaviour of the plant becomes subordinated within that of the population, with implications for genotyping, phenotyping and plant breeding. [ABSTRACT FROM AUTHOR]

The evolution in the definition of crop yield—from the ratio of seed harvested to seed sown to the contemporary measure of mass of seed per unit land area―has favoured less competitive phenotypes. Here we use binary mixtures of cultivars spanning five decades of selection for yield and agronomic adaptation to ask three questions. First, what is the degree of symmetry in the response of yield to neighbour; this is, if an older, more competitive cultivar increases yield by 10% with a less competitive neighbour in comparison to pure stands, would the newer, less competitive cultivar reduce yield by 10% when grown with older neighbour. Lack of symmetry would indicate factors other than competitive ability underly yield improvement. Second, what are the yield components underlying competitive interactions. Third, to what extent are the responses to neighbour mediated by radiation, water and nitrogen. A focus on yield components and resources can help the interpretation of shifts in the crop phenotype in response to selection for yield. The rate of genetic gain in yield over five decades was 24 kg ha−1 year−1 or 0.61% year−1. A strongly symmetrical yield response to neighbour indicates that yield improvement closely associates with a reduction in competitive ability. Response to neighbour was larger for grain number and biomass than for grain weight and allocation of biomass to grain. Under our experimental conditions, competition for radiation was dominant compared to competition of water and nitrogen. High‐yielding phenotypes had lower competitive ability for radiation but compensated with higher radiation use efficiency, a measure of canopy photosynthetic efficiency. Genetic and agronomic manipulation of the crop phenotype to reduce competitive ability could further improve wheat yield to meet the challenge of global food security. [ABSTRACT FROM AUTHOR]

Wheat, rice, and maize collectively provide the bulk of energy and protein to the human diet worldwide. Over the last seven decades, China increased 5.8-fold the aggregated production of the three cereals, but further gains are required to meet the predicted demand of 776 Mt. by 2030. Here, we report the rate of genetic gain in yield of 0.65% year-1 for wheat between 1937 and 2012, 0.69% year-1 for rice between 1934 and 2011, and 0.77% year-1 for maize between 1950 and 2014 in China. National farm yield in the same periods increased 1.38% year-1 for wheat, 1.15% year-1 for rice and 1.32% year-1 for maize. Hence, genetic improvement (G) accounted for 47%-60% of the increase in farm yield, with improved management (M) and G × M interaction accounting for the balance. The absolute rate of genetic gain (kg ha-1 year-1) was proportional to environmental potential. Genetic gain in nitrogen utilization efficiency (yield per unit nitrogen uptake) was significant for all three crops and was achieved at the expense in grain N concentration that decreased at 0.19% year-1 in rice and 0.47% year-1 in maize. To guarantee future food security and environmental sustainability, breeding and agronomic efforts need to increase the rate of gain in yield and revert the declining trends in grain protein by improving nitrogen uptake and nitrogen harvest index. [ABSTRACT FROM AUTHOR]

Science historian James Burke, scientist turned writer Isaac Asimov and polymath Stuart Kauffman have all argued, from different angles, that technology is unavoidable, directional, combinatory, disruptive and unpredictable. They also highlight the unintended consequences of technology seeking to fix a problem and creating new problems and opportunities. Here I draw on their vision to outline these features of technology with a focus on sustainable agriculture and highlight their implications for investment in research and development, and connecting public policy and technological change. [ABSTRACT FROM AUTHOR]

This article is part of a series of brief commentaries to highlight papers that have resulted in important and distinctly new perspectives in crop science. Here, we outline a series of two papers by French and Schultz (F&S) on water use efficiency of wheat (Triticum aestivum L.) published in 1984. The insight of F&S was not to draw a regression line across their yield‐evapotranspiration data. Instead they saw an upper limit of 20 kg ha−1 mm−1 that, less than a decade after publication, was widely used by Australian farmers to benchmark their crops and identify causes of yield gaps. Over the last two decades, F&S‐type benchmarks have been expanded beyond wheat and beyond Australia to include sunflower (Helianthus annuus L.) in Argentina, maize (Zea mays L.) and wheat in the United States and China, and millet [Pennisetum glaucum (L.) R. Br.] in West Africa, among others. More recently, the concept of yield gap analysis based on a upper limit of yield per unit resource uptake has been successfully extrapolated to N. The N uptake per millimeter of water required to meet the water‐limited yield potential (0.65 kg N ha−1 mm−1 under their original conditions) is a hidden insight in the work of French and Schultz; it has been recently rediscovered in the context of crop improvement, co‐limitation theory, and drought‐induced N deficit. Perhaps more deeply, French and Schultz shifted farmers mindset from the mildly fatalistic idea of "drought" to the notion that many other factors were typically limiting crop yield, and the quantitative challenge of attaining a plausible benchmark. [ABSTRACT FROM AUTHOR]

Highlights • Genetic gains of Australian wheat were associated with higher water-nitrogen co-limitation. • Higher water-nitrogen co-limitation associated with a higher nitrogen uptake per unit of evapotranspiration. • Nitrogen traits are critical for drought adaptation. Abstract The interactions between nitrogen (N) and water are manifold, and the concept of co-limitation provides a quantitative framework for integration. This paper tested the hypothesis that selection for yield increased water-N co-limitation in wheat adapted to winter rainfall environments of Australia. To test this hypothesis, we measured evapotranspiration, N uptake and yield in a historic collection of varieties released between 1958 and 2007 (exp. 1) and between 1969 and 2015 (exp. 2). Crops were grown under 5 (exp. 1) or 4 (exp. 2) environmental conditions resulting from the combination of sites, seasons, and supply of N and water. Genetic gain of yield, i.e. the slope of the regression between yield and year of release was 14–24 kg ha−1 y−1 or 0.36–0.52% y−1. This yield gain was associated with a linear increase in water-N co-limitation, in turn associated with an increase in N uptake per mm of evapotranspiration at a rate of 0.0019 kg N mm−1 y−1. Our findings highlight the critical role of nitrogen for the adaptation of wheat to low rainfall environments, and the scope for further yield improvement based on traits that integrate resources. [ABSTRACT FROM AUTHOR]

Highlights • Root pruning improved wheat grain yield, HI and WUE by 6–11%. • Root pruning in spring performed better than that in winter. • Root pruning was more effective at high seeding rate in low-yielding conditions. • Root pruning improved apparent translocation of water soluble carbohydrates. Abstract Improved management practices are necessary to increase grain yield and water-use efficiency of rainfed winter wheat in semiarid environments. Yield and its components, evapotranspiration, and accumulation and apparent remobilisation of stem water soluble carbohydrates (WSC) were measured to understand the effects of root pruning and its interactions with seeding rate, water and nitrogen supply. Two factorial studies under straw mulching with continuous wheat were established in the Loess Plateau of China. Study 1 was repeated over four seasons and included six treatments from the combination of three root treatments, i.e. root pruning in winter before dormancy (RPw), root pruning at the re-green stage in spring (RPs) and untreated control (CK), and two seeding rates. Study 2 was repeated over three seasons and included twelve treatments from the combination of two root treatments (RPs and CK), two nitrogen rates and three pre-sowing soil water levels. Yield ranged from 2571 to 7722 kg ha−1, harvest index from 0.28 to 0.56, and water-use efficiency from 5 to 20 kg ha−1 mm−1. Root pruning improved grain yield, harvest index and water-use efficiency by 6–11% across environmental conditions. Grain yield increased more (i) by pruning roots in spring than in winter, (ii) in high plant density than in low plant density crops, and (iii) in low-yielding conditions. It is concluded that spring root pruning is a viable option to improve wheat yield and water use efficiency under straw mulching in semiarid environment. [ABSTRACT FROM AUTHOR]

Highlights • Yield correlated with five senescence traits from NDVI-time curves. • No correlation for yield between environments in 5 out of 6 comparisons (broad sense heritability = 0.39). • All senescence traits correlated negatively with concentration of water soluble carbohydrates at anthesis. • Water soluble carbohydrates correlated between environments in 6 out of 6 comparisons (broad sense heritability = 0.89). • Selection for low concentration of WSC could improve yield by improving both grain number per m2 and leaf area duration. Abstract High throughput phenotyping of canopy senescence based on Normalized Difference Vegetation Index (NDVI) could be useful in plant breeding. The aim of this paper was to assess the association between grain yield and canopy senescence quantified with NDVI in oat lines selected for grain yield and milling quality. Sixteen lines were grown in four winter-rainfall environments where logistic curves between NDVI and thermal time from anthesis (GS60) were fitted to return five traits: maximum NDVI, NDVImax ; minimum NDVI, NDVImin ; thermal time to 50% senescence, x50; rate of senescence, rate; and the area under the NDVI curve, area. Across sources of variation, residuals of yield after removing the effect of phenology correlated with area (r = 0.69), NDVImax (r = 0.67), x50 (r = 0.57), NDVImin (r = 0.51) and rate (r = −0.30), all significant at P < 0.05. All five senescence traits correlated negatively with concentration of water soluble carbohydrates at anthesis, particularly area (r = −0.75, P < 0.0001). There was no correlation for yield between environments in 5 out of 6 comparisons (broad sense heritability = 0.39) and water soluble carbohydrates correlated between environments in 6 out of 6 comparisons (broad sense heritability = 0.89). Correlations between environments were irregular for senescence traits. Selection for low concentration of water soluble carbohydrates could increase oat grain yield by improving both grain number per m2 and leaf area duration. [ABSTRACT FROM AUTHOR]

Highlights • Grain quality associated with environmental conditions between GS31 and 200 °Cd after flowering. • In stressful environments, trade-offs between yield and quality were important. • Water soluble carbohydrates were the crux of these trade-offs. • Breeding targets "specialist" phenotypes for grain and fodder but traits meeting market standards spread across types. • "Generalist" phenotypes can accommodate multiple agronomic uses but specialists are required where trade-offs are involved. Abstract The profitability of oat crops depends on quality attributes in relation to milling and hay marketing standards. The aims of this paper were to (i) quantify grain and hay quality traits in varieties and advanced grain, hay and grazing oat lines, and (ii) analyse the effect of line, environment and their interaction from the viewpoint of phenotypic plasticity. The experiment included 29 lines grown in the winter-rainfall region of South Australia. Grain traits included hectolitre weight, screenings, groat percentage, brightness and concentration of oil and protein. Hay traits, measured at GS71, included digestibility, crude protein, water soluble carbohydrates, acid detergent fibre, and neutral detergent fibre. High temperature, high vapour pressure deficit, and water deficit in the developmental window from GS31 to 200 °Cd after GS60 reduced hectolitre weight and groat percentage, and increased screenings. For hay, the proportion of water soluble carbohydrates declined, the proportion of both acid detergent fibre and neutral detergent fibre increased, and digestibility decreased with higher minimum temperature in a window from approx. −500 to +500 °Cd centred at anthesis. For both grain and hay, current lines returned high yield and high quality in favourable environments, where further improvement could focus on yield and maintenance of quality. In stressful environments, trade-offs between yield and quality were important; water soluble carbohydrates were the crux of these trade-offs. For grain, high concentration of water soluble carbohydrates favoured high hectolitre weight, low screenings and high groat percentage, at the expense of yield. For hay, high concentration of water soluble carbohydrates associated with higher digestibility and lower fibre, at the expense of yield. Nitrogen adds a layer of complexity to these relations, which were partially captured by leaf greenness measured with SPAD. Greener leaves associated with lower concentration of water soluble carbohydrates, hence capturing the established negative correlation between nitrogen and water soluble carbohydrates. Greener leaves associated positively with yield and protein concentration in grain and hay, lower digestibility and higher neutral (and acid) detergent fibre. Whereas the breeding program targets "specialist" phenotypes for grain and fodder, quality traits meeting market standards were spread across types. "Generalist" phenotypes can accommodate multiple agronomic uses but specialists are required where trade-offs are involved. [ABSTRACT FROM AUTHOR]

Insufficient nitrogen applications may contribute to yield gaps in low rainfall environments of Western Australia (WA). This study tested a nitrogen nutrition index (NNI) for wheat tailored for low rainfall regions, which is based on rainfall-scaled dilution curves. We analyzed yield, shoot biomass, and nitrogen concentration from 32 field trials in WA. An empirical rainfall threshold of 400mm (summerþgrowing season rainfall) returned two parallel dilution curves accounting for the reduction of critical N in drier and lower yielding conditions. Scatterplots of relative yield and rainfall-adjusted NNI returned a robust boundary function that may lead to greater adoption by growers. The NNI defined in this research study can be applied and further tested by growers in WA, but may also apply to other low rainfall environments, to close nitrogen related yield gaps. [ABSTRACT FROM AUTHOR]

On historical timescales, enhanced availability of water and nitrogen has been a major driver of improved crop yield worldwide. The interaction between water and nitrogen has received attention, but theories and conceptual tools lag behind our fast-increasing capacity to monitor crop nitrogen and water status using remote sensing. Theory, mostly developed in ecology, predicts that plant growth is maximized when all resources are equally limiting. Therefore, for a given level of stress, growth is maximized under colimitation of resources. The concept of colimitation is less developed in agriculture, where the notion of sequentially, single limiting factors has been dominating since von Liebig law of minimum. During the last two decades, the concept of colimitation of resources has been used to explain yield gaps in wheat, barley, and canola in Mediterranean-type environments of Australia and Europe, and in maize in the Pampas of Argentina. These studies conform to theory: high yield is usually associated with high water and N colimitation. In view of the increasing capacity to measure crop water and N status of crops using remote sensing, we reviewed N-water colimitation as this concept provides a robust framework to integrate otherwise dispersed measurements. First, we revise the concept of colimitation in terms of timescale, level of organization, and thropic level; an agronomic definition of colimitation is advanced. Second, we outline the methods to quantify colimitation between two resources in a generalized crop model, and between water and nitrogen in particular. Third, we summarize studies providing experimental and modeling evidence of colimitation. A notion of crop yield at the biophysical "boundaries" of nitrogen and water use efficiency is presented within the colimitation context. Finally, we propose future directions to develop tools to quantify water-nitrogen colimitation using remote sensing. [ABSTRACT FROM AUTHOR]

Senescence is a key physiological process that can regulate crop grain yield. Patterns of leaf senescence and its association with grain yield for a short maturity maize hybrid were investigated in a factorial combination of two tillage treatments (conventional and no-till), three amounts of stubble (0, 3 and 5 t ha −1 ) and three N rates (0, 80 and 120 kg N ha −1 ) over three seasons in 2015 long rains, 2015/2016 short rains and 2016 long rains. Leaf senescence from flowering to harvest was assessed at (a) the whole-plant scale by the visual scoring of dry leaves and (b) the canopy-layer scale by measuring leaf greenness with a SPAD 502 chlorophyll meter. A bilinear model was used to quantify the patterns of senescence at the whole-plant scale. A logistic function was fitted to estimate the traits of senescence at three canopy layers (top, mid, bottom), including minimum and maximum SPAD, onset of senescence (EC90), time to loss of 50% maximum SPAD (EC50) and the rate of senescence in each layer. Nitrogen rate effect on patterns and traits of senescence were large and its interactions with stubble were more frequent than interactions between other treatments. Tillage and stubble amount had marginal effects. EC50 was delayed in the unfertilized controls compared with fertilized crops and was negatively correlated with grain yield. Rate of senescence was faster in fertilised crops compared with unfertilized controls at both whole-plant and canopy-layer scales. Grain yield, grain number and nitrogen remobilization efficiency were associated with faster rates of senescence in the top and mid leaves but with slower rates of senescence in the bottom layer leaves. We advance a sink-driven leaf senescence ideotype for high yield and efficient use of nitrogen for short maturity maize. [ABSTRACT FROM AUTHOR]

Oats likely emerged as part of the weedy grass assemblage in early wheat and barley crops. Some Avena species, such as A. fatua and A. sterilis, evolved into aggressive weeds, and the high interspecific competitive ability of cultivated oats (A. sativa) is valued agronomically to facilitate weed control in rotations. We tested the hypothesis, verified in many crops, that high yield of oats is related to low intraspecific competitive ability. Ten contemporary oat varieties, selected for grain yield and milling attributes, where grown in three environments. Response to competition was calculated as 100 x (Yb - Yc)/Yc, where Y is yield measured in border (b) and centre (c) rows. The same definition was used to calculate response to competition of yield components (biomass, harvest index, grain number, grain weight) and the components of grain number (panicle number and grains per panicle). Yield response to competition was affected by all three sources of variation, i.e. environment, variety and variety x environment interaction. The interaction demonstrates the plasticity of yield response to intraspecific competition; for example, the response to competition of variety Mortlock varied from 9% to 71% among environments. This plasticity in yield response to competition was partially related to variety-dependent responses to competition for biomass and harvest index, number of panicles and number of grains per panicle. We did not find the expected negative association between yield and variety-dependent response to competition. We discuss how this lack of correlation could relate to sampling issues, i.e. a limitation in the range of environments and varieties explored in this study, or reflect a legitimate feature of oat crops arising from early and contemporary selective pressures. [ABSTRACT FROM AUTHOR]

Controversy around the benefits of NT and stubble retention, and weaknesses in the underpinning science arise from a limited understanding of the mechanisms that operate in these systems. Two experiments were conducted at the Kenya Agricultural and Livestock Research Organization research station in Embu (0.515°S and 37.273°E) over three seasons during the 2015 long rains, 2015/2016 short rains and 2016 long rains to explore the mechanisms that regulate crop growth, nitrogen uptake and yield in maize ( Zea mays L.). In the first experiment, crops were grown in a factorial combination of conventional tillage (CT) and no-till (NT), three amounts of stubble (0, 3 and 5 t ha −1 ) and three N rates (0, 80 and 120 kg N ha −1 ). The second experiment investigated the interaction between tillage (CT, NT) and timing of N supply (80 kg N ha −1 ) that was supplied at sowing, six- (V6) and 12-leaf stage, with 5 t ha −1 of stubble. Grain yield ranged from 2.3 to 5.3 t ha −1 , with small effects from tillage and stubble retention. Nitrogen had the largest impact on grain yield and influenced crop response to tillage and stubble by modifying crop growth rate (CGR) and nitrogen nutrition index (NNI). However, the effects of N timing on crop growth, yield and traits associated with N use efficiency were independent of tillage system. High CGR between V6 and flowering was associated with high NNI, which led to increased grain number. The value of stubble in water storage at sowing, and crop growth and yield was greater in a dry season (<300 mm rainfall) compared with wet seasons (>600 mm). Irrespective of tillage system, moderate amounts of stubble, higher N rates and better matching of N supply to the critical window for yield determination could improve maize yields in sub-humid tropical environments. [ABSTRACT FROM AUTHOR]

Few studies have investigated changes over time in nutrient uptake and yield, in addition to the study of nutrient stoichiometry as a metric of nutrient limitations in soybean [Glycine max (L.) Merr.]. A comprehensive synthesisanalysis was performed by compiling a global historical soybean database of yield, total biomass, and nutrient (N, P, and K) content and concentration in studies published from 1922 to 2015. This period was divided in three eras based on genetically modified soybean events: Era I (1922-1996), Era II (1997-2006), and Era III (2007-2015). The main findings of this review are: (i) seed yield improved from 1.3 Mg ha-1 in the 1930s to 3.2 Mg ha-1 in the 2010s; (ii) yield increase was primarily driven by increase in biomass rather than harvest index (HI); (iii) both N and P HIs increased over time; (iv) seed nutrient concentration remained stable for N and declined for both P (18%) and K (13%); (v) stover nutrient concentration remained stable for N, diminished for P, and increased for K; (vi) nutrient ratios portray different trends for N/P (Era I and III > II), N/K (Era I > II and III), and K/P (Era II and III > I); (vii) yield per unit of nutrient uptake (internal efficiency) increased for N (33%) and P (44%) and decreased for K (11%); and (viii) variations in nutrient internal efficiency were primarily explained by increase in nutrient HI for N and K, but equally explained by both HI for P and seed P concentration. These findings have implications for soybean production and integrated nutrient management to improve yield, nutrient use efficiency, and seed nutrient composition. [ABSTRACT FROM AUTHOR]

We measured yield and its components, phenology, leaf greenness, and concentration of water soluble carbohydrates and concentration of nitrogen in shoots of 29 oat varieties to determine (i) the phenotypic plasticity of these traits as a means to capture genotype-by-environment interactions, (ii) the role of these traits and their plasticity in adaptation to drought, and (iii) putative trade-offs between drought adaptation and yield potential. Varieties spaned grain, hay and grazing types, and ranged from 1301 to 1927 °Cd from sowing to anthesis. Yield was measured in nine environments while other traits were measured in 4–7 out of the 9 environments. Averaged across varieties, yield varied from 0.3 to 4.2 t ha −1 . The main environmental drivers of yield were water supply:demand from 500 °Cd before to 500 °Cd after anthesis, and minimum temperature in the same period. Phenotypic plasticity of yield, quantified as variance ratio, ranged from 0.60 to 1.22 for grain types and from 0.28 to 1.06 for their grazing and hay counterparts; high yield plasticity was associated with an asymmetric response to growing conditions: yield increased 3.3 ± 0.28 t ha −1 per unit increase in plasticity under favourable conditions, and 0.6 ± 0.16 t ha −1 per unit increase in plasticity under stress. For our combination of varieties and environments, genotypes were better discriminated in favourable environments, where selection for high plasticity would improve both yield potential and drought adaptation. After accounting for plasticity, yield residuals revealed consistent phenological thresholds (943 °Cd for GS31, 1470 °Cd for GS60) for adaptation to both favourable and stressful conditions. Yield correlated with leaf greenness (SPAD), particularly during grain fill. As expected from theory, yield was closely related to grains per m 2 and weakly related to grain weight. Grains per m 2 were negatively related to concentration of water soluble carbohydrates in shoots, which were in turn negatively correlated with shoot nitrogen concentration. Under favourable conditions, some varieties maintained a high concentration (>20%) of water soluble carbohydrates at harvest. Selection against this trait could improve yield potential, but residual labile carbohydrates can also be exploited in dual grain-feed varieties, and can provide flexibility for hay growers when logistics preclude cutting at the common water ripe (GS71) target. [ABSTRACT FROM AUTHOR]

This study assessed changes in nitrogen (N) and phosphorus (P) uptake and partitioning in response to selection for yield in milestone varieties of Chinese winter wheat (Triticum aestivum L.). We established a factorial trial combining 11 nutrient–water regimes with three (2013–14) and five (2014–15) varieties released from 1970 to 2005. Grain yield increased at a rate of 0.46% year–1, with no apparent increase in the uptake of nutrients. Nitrogen harvest index did not change, and P harvest index increased at a rate of 0.15% year–1. Consequently, yield per unit N uptake and yield per unit P uptake increased at similar rates (0.4% year–1) at the expense of nutrient concentration in grain, which declined at a rate of 0.47% year–1 for N and 0.31% year–1 for P. No trends in N nutrition index were found. Selection for yield in wheat increased the yield per unit nutrient uptake at the expense of grain nutrient concentration. Further gains in yield need to be matched by increasing N uptake to maintain grain protein. Dilution of P in grain needs to be considered in terms of the putatively undesirable role of phytate for human nutrition, and the need for P reserves in seed for crop establishment. [ABSTRACT FROM AUTHOR]

Here, we show a unique crop response to intraspecific interference, whereby neighboring sunflower plants in a row avoid each other by growing toward a more favorable light environment and collectively increase production per unit land area. In high-density stands, a given plant inclined toward one side of the interrow space, and the immediate neighbors inclined in the opposite direction. This process started early as an incipient inclination of pioneer plants, and the arrangement propagated gradually as a "wave" of alternate inclination that persisted until maturity. Measurements and experimental manipulation of light spectral composition indicate that these responses are mediated by changes in the red/far-red ratio of the light, which is perceived by phytochrome. Cellular automata simulations reproduced the patterns of stem inclination in field experiments, supporting the proposition of self-organization of stand structure. Under high crop population densities (10 and 14 plants per m²), as yet unachievable in commercial farms with current hybrids due to lodging and diseases, self-organized crops yielded between 19 and 47% more oil than crops forced to remain erect. [ABSTRACT FROM AUTHOR]

Cropped area under no-till (NT) is increasing worldwide, but the extent to which breeding for yield is selecting for adaptation to NT is unclear. In addition, the consequences of selection for yield and that of tillage system on senescence patterns are not known. This study compared yield and senescence patterns of fourteen Australian wheat varieties released between 1958 and 2011, under no-till with stubble retention, and under conventional tillage (CT) without stubble. Grain yield increased at a rate of 21 kg ha −1 year −1 irrespective of tillage system, which implied that selection for yield did not improve wheat adaptation to no-till. Selection for yield changed the pattern of canopy senescence, whereby modern varieties had lower peak normalised difference vegetative index (NDVI), higher NDVI at maturity, a faster rate of senescence, and greener leaves, compared with older counterparts. [ABSTRACT FROM AUTHOR]

Late-season nitrogen (N) application has been proposed to boost grain yield and grain protein concentration (GPC) in cereals; however, its effects on bread and durum wheat have been inconsistent in field experiments. We performed a meta-analysis to (i) assess the effect of N applications to wheat after flag leaf visible (GS 37) on grain yield and GPC; and to assess the variation in these responses with (ii) N fertiliser management, (iii) environmental factors, and (iv) physiological traits. We searched ' Agronomy Journal ', ' Crop Science ', ' European Journal of Agronomy ', and ' Field Crops Research ' for articles published between 1980 and 2021 that allowed for a direct comparison of wheat yield and GPC between N application after GS 37 to an otherwise equally managed crop that received basal N fertilisation. We also collected other traits such as stover biomass and N uptake at plant maturity, and dough rheological properties, when available. The search resulted in 38 articles that, in addition to one unpublished trial from our group, evaluated 542 pairwise comparisons in 127 environments. Across studies, grain yield ranged from 1.15 to 10.63 Mg ha−1 and showed a negative relation with GPC, which ranged from 65 to 189 g kg−1. Late-season N fertilisation was consistently neutral for grain yield (I2, proportion of the overall variance due to variation in real effects rather than chance, 26.2 %) and increased GPC with a pooled estimate of 3.96 %. The response of GPC was heterogeneous (I2 = 84 %), suggesting the need for exploration of potential moderators of the response. Meta-regression suggested that increasing the proportion of late N relative to the total available N positively associated to increases in GPC, and the residuals of this analysis suggested that later applications increased GPC response, with no effect of N fertiliser source or placement. Environments with low temperature, high photothermal quotient, and long duration of the critical period associated with greater GPC response to late-season N applications. The relative response of GPC to late fertilisation correlated with the relative response of both stover N uptake and nitrogen concentration in stover at maturity, but not with stover biomass at maturity. Alveogram index and dough extensibility increased when late-season N increased GPC. Enhancing GPC through late N applications should consider associations between management, environmental, and physiological factors. Future research should focus on forecasting GPC response to late N, based on GPC response drivers identified in the current research. • Meta-analysis highlighted physiological drivers of wheat response to late N • Grain yield was unaffected by late N across a broad range of environments • Late N increased protein by 3.96% and its effects were heterogeneous • Protein increased linearly with the proportion of late N and with later applications • Higher protein response to late N associated to favourable growing conditions [ABSTRACT FROM AUTHOR]

Robust associations between yield and crop growth rate in a species-specific critical developmental window have been demonstrated in many crops. In this study we focus on genotype-driven variation in crop growth rate and its association with chickpea yield under drought. We measured crop growth rate using Normalised Difference Vegetative Index (NDVI) in 20 diverse chickpea lines, after calibration of NDVI against biomass accounting for morphological differences between Kabuli and Desi types. Crops were grown in eight environments resulting from the combination of seasons, sowing dates and water supply, returning a yield range from 152 to 366 g m −2 . For both sources of variation – environment and genotype – yield correlated with crop growth rate in the window 300 °Cd before flowering to 200 °Cd after flowering. In the range of crop growth rate from 0.07 to 0.91 g m −2 °Cd −1 , the relationship was linear with zero intercept, as with other indeterminate grain legumes. Genotype-driven associations between yield and crop growth rate were stronger under water stress than under favourable conditions. Despite this general trend, lines were identified with high crop growth rate in both favourable and stress conditions. We demonstrate that calibrated NDVI is a rapid, inexpensive screening tool to capture a physiologically meaningful link between yield and crop growth rate in chickpea. [ABSTRACT FROM AUTHOR]

Drought affects the growth of legumes directly, and indirectly, by reducing total nitrogen fixation. Here, we compiled published data to compare the sensitivity to water deficit on plant growth and total nitrogen fixation traits, i.e., the number of nodules per plant, average nodule mass, and nitrogen fixation per unit nodule mass. Hierarchies of phenotypic plasticity have been established for seeds and organelles, whereby variation in number associates with conserved size. By analogy, our first hypothesis is that there is a hierarchy of plasticities between nitrogen fixation traits. Our second hypothesis is that determinate nodules are more sensitive to water deficit than their indeterminate counterparts, because the latter can reactivate meristems when water becomes available. In our sample, onset of stress treatment averaged 28 d after sowing; median duration of stress was 12 d; and intensity of stress (ratio of shoot biomass between stressed and control) averaged 0.65. These drought conditions (i) reduced total nitrogen fixation and average nodule mass more severely than plant shoot mass, (ii) elicited a hierarchy of plasticities whereby number of nodules per plant varied substantially, and average nodule mass and nitrogen fixation per unit nodule mass were relatively conserved, and (iii) affected more severely Milletioids (determinate, ureide exporting nodules) than their IRLC counterparts (indeterminate, amide exporting nodules). • Total N fixation was partitioned as nodule number, average nodule mass, and nitrogen fixation per unit nodule mass. • Early-season drought reduced nodule number more than average nodule mass and N fixation per unit nodule mass. • Drought effect were more severe in Milletioid (determinate, ureide) than in IRLC (indeterminate, amide) nodules. [ABSTRACT FROM AUTHOR]

We measured yield components, nitrogen fixation, soil nitrogen uptake and carbon isotope composition (δ13C) in a collection of chickpea genotypes grown in environments where water availability was the main source of yield variation. We aimed to quantify the phenotypic plasticity of these traits using variance ratios, and to explore their genetic basis using FST genome scan. Fifty-five genes in three genomic regions were found to be under selection for plasticity of yield; 54 genes in four genomic regions for the plasticity of seeds per m2; 48 genes in four genomic regions for the plasticity of δ13C; 54 genes in two genomic regions for plasticity of flowering time; 48 genes in five genomic regions for plasticity of nitrogen fixation and 49 genes in three genomic regions for plasticity of nitrogen uptake from soil. Plasticity of yield was related to plasticity of nitrogen uptake from soil, and unrelated to plasticity of nitrogen fixation, highlighting the need for closer attention to nitrogen uptake in legumes. Whereas the theoretical link between δ13C and transpiration efficiency is strong, the actual link with yield is erratic due to trade-offs and scaling issues. Genes associated with plasticity of δ13C were identified that may help to untangle the δ13C-yield relationship. Combining a plasticity perspective to deal with complex G×E interactions with FST genome scan may help understand and improve both crop adaptation to stress and yield potential. [ABSTRACT FROM AUTHOR]

Natural selection does not lead to optimal solutions due to trade-offs and environmental variation, genetic and developmental constraints, and historical contingency. In this paper we propose that constraints like these also often apply to the improvement of both crop varieties and management practices, creating a dual biological and agronomic barrier for the optimisation of crops. We discuss constraints on optimisation of 1) crop ancestors, by natural selection, 2) crop traits, by artificial selection and biotechnology, and 3) crop management. We outline how trade-offs and environmental variation make single-factor optimisation (e.g. “optimum leaf angle” or “optimal fertiliser rate”) impossible. Definitions of “optimal” that recognise trade-offs and variability can help, but we argue there are major constraints on even those forms of optimality. Optimality theory may be useful to formulate null hypotheses, however, as divergence between actual traits and theoretical optima can highlight constraints that are biologically interesting and agronomically relevant. Understanding the nature and size of these constraints can help us map more likely pathways for future improvements in agriculture. [ABSTRACT FROM AUTHOR]

Against the backdrop of climate change, genotypes with improved adaptation to elevated temperature are required; reliable screening methods are therefore important. Sowing date experiments are a practical and inexpensive approach for comparison of large collections of lines. Late-sown crops usually experience hotter conditions and phenotypes thus partially capture this environmental influence. Two sets of confounded factors, however, limit the value of sowing date trials. First, daily mean temperature correlates with both minimum and maximum temperature, photoperiod, radiation and vapour pressure deficit, and it may also correlate with rainfall. Second, temperature alters the genotype-dependent phenology of crops, effectively shifting the timing and duration of critical periods against the background of temperature and other environmental variables. Here we advance a crop-level framework to unscramble the confounded effects of sowing date experiments; it is based on four physiological concepts: (1) annual crops accommodate environmental variation through seed number rather than seed size; (2) seed number is most responsive to the environment in species-specific critical windows; (3) non-stressful thermal effects affecting seed set through development and canopy size can be integrated in a photothermal quotient relating intercepted photosynthetically active radiation (PAR) and mean temperature during the critical window; (4) stressful temperature reduces yield by disrupting reproduction. The framework was tested in a factorial experiment combining four chickpea varieties with putatively contrasting adaptation to thermal stress and five environments resulting from the combination of seasons and sowing dates. Yield ranged from 13 to 577 g m −2 . Shifts in phenology led to contrasting photothermal conditions in the critical window between flowering and 400 °C d after flowering that were specific for each variety–environment combination. The photothermal quotient ranged from 2.72 to 6.85 MJ m −2 °C −1 ; it explained 50% of the variation in yield and maximum temperature explained 32% of the remaining variation. Thus, half of the variation in yield was associated with developmental, non-stressful thermal effect and (at most) 16% of the variation was attributable to thermal stress. The photothermal quotient corrected by vapour pressure deficit accounted for by 75% of the variation in yield and provided further insight on photosynthesis-mediated responses to temperature. Crop adaptation to non-stressful, developmental thermal effects and stressful temperatures disrupting reproduction involve different physiological processes and requires partially different agronomic and breeding solutions. Our analytical approach partially separates these effects, adds value to sowing date trials, and is likely to return more robust rankings of varieties. [ABSTRACT FROM AUTHOR]

Chickpea seed yield is highly variable as a result of biotic, mostly fungal, and abiotic stresses including extreme temperatures and water stress. The effect of stress on yield depends on its intensity, timing and duration, hence the importance of knowing the critical window of yield formation and stress vulnerability. This window has not been determined in chickpea. To fill this gap, we compared the effect of sequential 14-d shading periods on the yield and yield components of two chickpea varieties, PBA Boundary and PBA Slasher, in three environments where unshaded controls yielded between 2880 and 3130 kg ha −1 . Unlike other species which do not respond to stress early in the season, shading reduced yield from emergence until the beginning of the critical period, 300 °Cd before flowering (base temperature = 0 °C). The critical period was found to be at least 800 °Cd long centred 100 °Cd after flowering. Seed number accounted for most of the variation in yield, which was unrelated to seed size. Pod number accounted for most of the variation in seed number prior to the critical period, while pod number and seeds per pod contributed to seed number within the critical period. After 400 °Cd post flowering, seeds per pod was the main variable affecting seed number. This information can be used in breeding and agronomy to improve stress adaptation. [ABSTRACT FROM AUTHOR]

The nitrogen economy of the crop is a critical driver of biomass and grain production, and its importance is reflected in a large, worldwide research effort to link nitrogen, growth and yield. Particular research questions require measurement of specific traits, hence the need to quantify multiple, often complementary traits including crop nitrogen uptake, nitrogen use efficiency and its components, nitrogen concentration in the crop and its parts, down to relevant enzymes (e.g. nitrate reductase) and other products of gene expression. Nitrogen uptake, however, is co-regulated by both soil nitrogen availability and crop biomass accumulation; hence, crop nitrogen uptake or shoot nitrogen concentration reflect univocally crop nitrogen status only if comparisons are made at similar biomass. Although the allometric relationships between biomass and nitrogen uptake have been established for over two decades, many studies still report results in terms of nominal treatments, e.g. high vs low nitrogen, which are uninformative; curves relating yield and fertiliser rate, which are of local interest but provide little insight on the underlying processes and have low generic value; and nitrogen-related traits that are incomplete or inadequate to quantify crop nutrition status. Often, the allometric relationships between nitrogen and biomass are overlooked. In this opinion paper, we summarise the already well established concepts of dilution curves and nitrogen nutrition index, outline the standard partitioning of nitrogen use efficiency, and highlight the confounded effects in nitrogen use efficiency when the allometric relationship between nitrogen uptake and biomass is ignored. A sample of recent papers is used to survey the most common approaches to characterise nitrogen related traits. We illustrate the application of dilution curves and nitrogen nutrition index in the assessment and interpretation of crop responses to agronomic practices and comparisons of wheat cultivars and maize hybrids. [ABSTRACT FROM AUTHOR]

Rainfed crops rely on two sources of water: stored soil water at sowing and seasonal rain. In strongly seasonal winter-rainfall environments, stored soil water at sowing is minor, and uncertain seasonal rainfall is a source of risk. In south-eastern Australia, under-fertilisation is a common outcome of nitrogen risk management with implications for wheat yield and mining of soil organic matter. Here we explore the use of carbon isotope composition (δ 13C) to capture the effects of crop water status on grain yield in a context of nitrogen top dressing. In the sampled environments, crops receive at least 50% of seasonal rainfall by stem elongation, and at least 70% of seasonal rainfall by flowering. In a sample of 1518 plots, yield varied from 0.07 to 9.96 t ha-1 and correlated with δ 13C measured with isotope ratio mass spectrometer (IRMS) at flowering (r = −0.76, p < 0.0001); this is consistent with the rainfall pattern and the physiology of the crop featuring a critical period for yield from 300 °Cd before to 100 °Cd after anthesis. In a sample of 135 plots, yield varied from 1.2 to 8.4 t ha-1 and correlated with δ 13C measured with IRMS at stem elongation (r = −0.56, p < 0.0001). Yield response to nitrogen, defined as the difference between yield in fertilised crops (50–200 kg N ha-1) and unfertilised controls, correlated with δ 13C measured with IRMS at stem elongation, except for late-sown crops. Mid-infrared spectroscopy (MIR) returned estimates of δ 13C that agreed with δ 13C measured with IRMS (calibration: R2 = 0.82, RMSE = 0.53‰, n = 833; validation: R2 = 0.70, RMSE = 0.75‰, n = 364). We conclude that a MIR based, high-throughput, affordable measurement of δ 13C could be scaled to guide nitrogen management of wheat in winter-rainfall environments. • In a sample of 1518 plots, yield varied from 0.07 to 9.96 tha-1 and correlated with δ 13C at flowering. • Yield response to nitrogen correlated with δ 13C at stem elongation, except for late-sown crops. • Mid-infrared spectroscopy is a cost-effective, high-throughput approach to estimate δ 13C for agronomic applications. [ABSTRACT FROM AUTHOR]

Owing to the high contents of oil and protein, soybean [Glycine max L. (Merr.)] seeds are energy-rich. Genetic improvement of soybean yield is linked to the dilution in seed protein; changes in low-energy compounds such as carbohydrates have received less attention. We tested the hypothesis that selection for yield in soybean has shifted seed composition in favor of low-energy compounds. We characterized the dynamics of three seed fractions (protein, oil, and residual) during seed filling in seven commercial soybean varieties released between 1980 and 2013 in a two-year field experiment. Genetic gain in yield was linked with reduced seed energy cost: seed protein concentration decreased by 0.06% yr−1, oil remained stable, and the residual fraction increased by 0.09% yr−1. Seed accumulation of the residual fraction revealed a shorter lag phase and a longer effective filling period for the modern relative to the older soybean varieties. Seed energetic requirement significantly decreased − 0.06% yr−1. Resource availability per seed during the seed-filling period was not limiting across all tested varieties. Further research is warranted on the biochemical nature of the residual fraction, and on the implications of seed composition for future breeding, soybean meal and end uses. [ABSTRACT FROM AUTHOR]

Highlights: [•] Review of phosphorus, potassium and sulphur effect on symbiotic N2 fixation. [•] Nodule mass and number are more responsive to nutrient deficit than shoot biomass. [•] N2 fixation is more responsive to P and K deficit than shoot and nodule mass. [•] The ratios N/K, N/P and N/S in shoots increased under nutrient deficiency. [•] Patterns of growth, N2 fixation and nutrient concentration were similar for P, K and S deficiency. [ABSTRACT FROM AUTHOR]

Abstract: Using large-scale open-top chambers to approximate the thermal regimes of the Barossa Valley in the next decades, we measured yield and vegetative growth of grapevines in three factorial field experiments combining two thermal regimes (elevated temperature vs. control) with: two water regimes (experiment 1), two source:sink ratios generated by manipulation of fruit load (experiment 2) and four varieties (experiment 3). Water regime, source:sink ratio and varieties are sources of variation typically embedded in climate change studies using time series. Yield of controls ranged from 1.2 to 10.5kgvine−1. Warming had asymmetric effects on fruit yield and fruit/pruning weight ratios: yield response to elevated temperature varied from 46% reduction to 177% increase in relation to controls, and the response of fruit/pruning weight ratio varied from 56% reduction to 145% increase. Yield response to temperature was primarily explained by the response of bunch number (r 2 =0.92, P <0.0001). The effect of elevated temperature on fruit/pruning weight ratio was closely related to the response of fruit yield (r 2 =0.79, P <0.0001) and unrelated to the response of pruning weight (P =0.18). Elevated temperature reduced concentration of starch in trunks but not in roots. We conclude that the asymmetric responses of yield and fruit/pruning weight ratios resulted from seasonal influences on warming effects, whereby the largest responses of these traits were mediated by the promotion of bunch formation following relatively low temperatures in the preceding season. This highlights the need to assess warming effects in the light of both the background temperature and the distribution of thermally contrasting seasons in particular locations. Lower source:sink ratio and reduced starch concentration in trunks are two important elements of the carbon balance of the vine with long-term physiological and viticultural implications. [Copyright &y& Elsevier]

Background and Aims: Barley breeding has increased yield over the last century, but the associated changes in the phenotype are largely unknown. Our aim was to quantify the rate of genetic gain in a collection of Australian barley cultivars representing seven decades of breeding, and the associated changes in the phenotype. Methods: Thirteen barley cultivars were grown in the field at Roseworthy and Mintaro, South Australia, to evaluate shifts in phenology, yield, and its components. A subset of five cultivars was grown under controlled conditions to probe for changes in root traits and nutrient uptake. Results: Grain yield increased at 16.0 ± 5.3 kg ha−1 yr−1 or 0.43 ± 0.15% yr−1 at Roseworthy, where average yield was 3.1 t ha−1. There was no relation between yield and year of registration at Mintaro, where severe, extended frost disrupted reproduction. Changes in phenology with year of registration were not apparent. The main drivers of yield gain were grain number per m2 and harvest index, with a minor contribution of shoot biomass. Root length density, specific root length, root extension rate, and nutrient uptake per cm of root length increased with year of registration. Conclusions: The rate of genetic gain of Australian barley aligned with rates reported for other breeding programs worldwide and compared to 21.0 ± 2.3 kg ha−1 yr−1 for actual yield in Australian farms between 1961 and 2019. Changes in the growth and functionality of the root system highlight the indirect effects of selective pressure for yield and agronomic adaptation. [ABSTRACT FROM AUTHOR]

Abstract: Yield components are relatively easy to measure and their interpretation is intuitive. However, strong environmental influences, genetic and physiological controls, and evolutionary constraints collectively lead to lack of independence among yield components that restrict their value in breeding and agronomic applications. Here, we first sketch a framework of plant responses to environmental factors to highlight the modulation of yield components by resources and their interplay with non-resource factors including developmental cues (e.g. maternal effects), extreme events (e.g. frost), predicting factors (e.g. photoperiod) and synchronising and integrating information (e.g. spectral composition of light). We suggest that, to the extent that non-resource cues allow plants to predict future availability of resources, simple resource-based models may be sufficient to capture the macroscopic responses of yield components to the environment. Next, we expand the original concept of hierarchy of plasticities between grain size (a relatively stable trait) and grain number (a plastic trait) to test the hypothesis of a broader hierarchy in the plasticities of yield components. Using published data for wheat, rice, barley and triticale, we verified that heritabilities capture the established hierarchy between plasticity of grain size and number. Median heritabilities of 0.31 for tiller number, 0.58 for inflorescence number, 0.59 for grains per inflorescence, and 0.79 for grain size supported the hierarchy of plasticities: tiller number > inflorescence number ≈ grains per inflorescence > seed size. The heritability of grain yield was consistently higher than the heritability for tillering, consistently lower than the heritability for grain size, and suggestively close to the heritability of inflorescence number and grains per inflorescence, the components of grain number per unit ground area. We conclude that understanding the environmental regulation of yield components in cereals would benefit from a dual focus on yield-related traits per se and their plasticity. [Copyright &y& Elsevier]

Abstract: In a worldwide context of agricultural intensification, cropping systems in Mediterranean-type environments have been reducing the frequency of long-fallow in a shift to continuous cropping. The focus of this paper is the short summer fallow between successive winter grain crops in environments of South Australia with winter-dominant rainfall. Our aims were to (i) estimate wheat yield response to summer rainfall, (ii) explain yield responses in terms of capture and efficiency in the use of radiation and water, (iii) explore the incidence of the amount and disposition of stubble on storage of summer rainfall, and (iv) assess the interaction between summer rainfall and nitrogen supply. We used trickle irrigation to manipulate summer water supply in two factorial experiments combining water and stubble treatments, and three factorials combining water and nitrogen supply. Addition of 50–100mm of water increased soil water content at sowing between 8 and 46mm compared to controls that only received the background summer rainfall (10–74mm). Yield gain from additional water input in summer declined from 1.1tha−1 to zero when the yield of controls increased from 2.0 to 7.8tha−1. Where yield response was related to a single resource, water or nitrogen, capture of radiation and water were major drivers of growth and yield response. Where yield response was related to the interaction between water and nitrogen, both capture and efficiency in the use of resources were important. Amount (0–5tha−1) and disposition of stubble (standing or flat) did not affect the amount or distribution of water in soils, and had no effect on grain yield. High nitrogen rate was critical to capture the benefits of additional summer water and reciprocally high water supply was required to capture the benefits of nitrogen fertilisation; this highlights the resource co-limitation for wheat production in these environments. In a water×nitrogen factorial, crops with either low nitrogen or no additional summer water supply had radiation use efficiency ∼1.6gMJ−1, biomass per unit evapotranspiration ∼33kgha−1 mm−1 and yield per unit evapotranspiration ∼15kgha−1 which increased to 1.9gMJ−1, 40kgha−1 mm−1 and 18kgha−1 mm−1 in crops with both additional water and high nitrogen. Across experiments and treatments, grain number accounted for 88% of the variation in yield. Grain number was proportional to crop growth rate between stem elongation and anthesis; crops with high nitrogen produced 116±5.0 grains per unit crop growth rate and their low nitrogen counterparts 99±4.6. Building evidence from Mediterranean environments worldwide highlights the importance of grain number as the main source of variation in yield and therefore the critical period between stem elongation and anthesis where both water and nitrogen supply are critical. [Copyright &y& Elsevier]

Conceptual models accounting for the influence of source:sink ratio on water relations of trees are theoretically relevant from a physiological perspective and practically important for irrigation scheduling. Midday stem water potential of horticultural trees often declines with increasing crop load but the actual response depends on environmental, management and plant factors. Here we advance a quantitative synthesis of the response of stem water potential to crop load from the perspective of phenotypic plasticity, defined as ‘the amount by which the expression of individual characteristics of a genotype are changed by different environments’. Data sets of stem water potential for contrasting crop loads were compiled for apple (Malus domestica L. Borkh.), olive (Olea europea L.), peach (Prunus persica L.), pear (Pyrus communis L.) and plum (Prunus domestica L.). Phenotypic plasticity of stem water potential was calculated as the slope of the linear regression between stem water potential for each crop load and the environmental mean of stem water potential across crop loads. Regression lines for trees with different crop load diverged with decreasing environmental mean stem water potential. For the pooled data, plasticity of stem water potential was a linear function of relative crop load. This represents a significant shift in perspective: the effect of crop load on the trait per se (stem water potential) is environmentally contingent, but the effect of crop load on the plasticity of the trait is not. We conclude that research on the effects of crop load on tree water relations would return more robust results if plant traits are considered from the dual perspective of the trait per se and its plasticity. [ABSTRACT FROM AUTHOR]

We used a water-centred framework (yield = transpiration × transpiration efficiency × harvest index) to investigate the effect of soil salinity on growth and yield of wheat and barley. Our working hypothesis is that salinity reduces transpiration proportionally more than transpiration efficiency. We established a glasshouse experiment with the factorial combination of four varieties (wheat: Janz, Krichauff; barley: Mundah, Keel) and three soil treatments: a control with no NaCl added, and NaCl added to achieve soil EC 0.75 dS m and 1.5 dS m. Pot-grown plants were watered to weight to determine transpiration and shoot dry matter was determined using a non-destructive image analysis system. Consistent with our hypothesis, salinity reduced transpiration (30-60%) proportionally more than transpiration efficiency (0-35%); transpiration accounted for 90% of the variation in shoot growth across varieties and treatments. Against this pattern, there were time- and variety-dependent responses. The rate of leaf appearance and the transpiration efficiency of Janz, Krichauff and Keel showed a two-stage response to salinity. In stage 1, salt-stressed plants maintained rate of leaf appearance and transpiration efficiency close to or slightly below those of the controls. After a clear break point where the slope changed, stage 2 was characterised by a substantial reduction in both traits. Stage 2 was not evident in salt-stressed Mundah, which maintained a relatively high rate of leaf appearance and transpiration efficiency. Across species, harvest index increased from 0.40 in controls to 0.47 at 0.75 dS m. Harvest index of plants grown at 1.5 dS m was unaffected in wheat, and was reduced in barley. We propose that an understanding of the effect of salinity on crop development, growth and yield requires integration of low-level traits in a framework of resource capture, resource-use efficiency and plant allocation. Osmotic stress tolerance, Na exclusion, and tissue tolerance to accumulated Na would improve yield of salt-stressed crops to the extent that these traits contribute to the maintenance of water uptake and harvest index. [ABSTRACT FROM AUTHOR]

Abstract: We measured the effects of increased daytime temperature during 2- (2007/08) or 3-week periods (2008/09) on the yield and yield components of irrigated Shiraz vines in the Barossa Valley of Australia. A simple and inexpensive open system was used to elevate temperature during a single phenological window, either bracketing budburst (E-L stage 4), shortly after flowering (E-L stage 23), bracketing pea size (E-L stage 31), around veraison (E-L stage 35) or shortly before harvest (E-L stage 38). Two important features of the heating systems were tracking of diurnal temperature dynamics, and maintaining relative humidity, hence avoiding the interaction between temperature and vapour pressure deficit. Minimum temperature was unchanged. Compared to controls, maximum ambient temperature was increased between 1.8 and 4.1°C in treated plots but canopy temperature of treated vines only increased by 0.9–1.1°C. Elevation of bunch temperature was 2.3–3.2°C. Increasing temperature around budburst transiently accelerated development in comparison to controls; no phenological changes were detected for other timings of treatment. Yield averaged 4.3kgvine−1 in 2007–08 and 6.1kgvine−1 in 2008–09. In both seasons and for all timings of treatment, increasing temperature did not affect yield or its components; lack of yield response did not result, therefore, from compensatory mechanisms, e.g. heavier berries compensating for fewer fruit. The dynamics of berry growth and total soluble solids were largely unaffected by temperature. Under our experimental conditions, the capacity of irrigated Shiraz canopies to partially buffer a 2–4°C increase in maximum ambient temperature may have been important for the maintenance of yield, and berry growth and sugar accumulation. [Copyright &y& Elsevier]

In response to suboptimal temperatures, temperate annual plants often increase root:shoot ratios, build-up carbohydrates and display typical morphological and anatomical changes. We know less about the responses of biennials such as carrot. As a model plant, carrot has the additional feature of two functionally and morphologically distinct root parts: the taproot, which stores carbohydrate and other compounds, and the fibrous root system involved in acquisition of water and nutrients. Here, we analyze the effects of temperature (12 vs 25°C) on growth, carbohydrate accumulation and whole-plant morphology in two carrot cultivars. Our working hypothesis is that suboptimal temperature favors active formation of reserve structures, rather than passive accumulation of storage carbohydrates. In comparison with plants grown at 25°C, plants grown at 12°C had: (1) higher fibrous root:shoot ratio (13%), (2) thicker (10–15%) and smaller (up to two- to three-fold) leaves, (3) lower leaf cuticular permeance (two- to four-fold), (4) higher taproot:shoot ratio (two-fold), (5) higher phloem:xylem ratios in taproot (two- to six-fold), (6) unchanged percentage dry matter content (%DMC) in leaves, petioles or fibrous roots and (7) higher %DMC in taproot (20%). However, %DMC of individual taproot tissues (phloem and xylem) was unaffected by temperatures and was consistently higher in the phloem (up to 30%). Therefore, the higher %DMC of whole taproots at 12°C was attributed solely to the increased development of phloem tissue. Carrot, therefore, shares many of the most conspicuous elements of temperate plant responses to low temperatures. Consistently with our hypothesis, however, carrots grown at suboptimal temperature promoted reserve structures, rather than the increase in carbohydrate concentration typical of most temperate annual species and woody perennials. [ABSTRACT FROM AUTHOR]

Simultaneously growing sinks are thought to compete for plant resources. Negative correlations, for example between grain number and stem mass in cereals, indeed resemble competition; but is the notion of intra-plant competition evolutionarily justified? Here we review intra-plant competition in light of two aspects of evolutionary biology: (a) major transitions that led to the reorganization of evolutionary individuals (e.g. isolated DNA molecules and independent cells) into new units of adaptation (e.g. chromosomes and multicellular organisms) with associated constraints to intra-individual conflict; and (b) genomic conflicts within individual plants with implications for resource allocation. Against this background, we look at apparent competition among genetically identical plant parts, and conclude that plants might use competition-like mechanisms to allocate resources, but only to the extent that these proximate mechanisms enhance overall plant fitness. In dealing with apparent competition among genetically different plant structures, we emphasize developing seeds attached to the same maternal plant, and the determination of yield components in annual crops. We propose that competition-like mechanisms among genetically different plant parts have been strongly shaped by the evolution of genomic conflict between parent and offspring, between female and male parents, and among siblings. By defining the number and potential size of grain simultaneously and before fertilization, a strong maternal control of resource allocation is exerted that favours uniform offspring size and partially counteracts genomic conflict. [ABSTRACT FROM AUTHOR]

• Splitting N in 3–4 applications improved wheat yield by 7 % and grain protein content by 5 %. • The effect of split N on yield was larger for winter wheat than for spring wheat. • Split N mitigated the negative relationship between yield and grain protein content. Management of nitrogen (N) fertilizer is critical to avoid the environmental consequences of both over-fertilization and excess reactive N in the system, and chronic under-fertilization and soil mining. Split N application seeks to improve nitrogen use efficiency in both small-holdings and large-scale mechanized farms, but lack of conclusive evidence on its benefits restricts the adoption of this practice. Here we report a global meta-analysis of split N application in wheat using 129 studies with 2661 comparisons. Split N in 3–4 applications improved yield by 7.0 % and grain protein by 5.2 % in relation to single application. The effect of split N on yield was larger for winter wheat than for spring wheat, while split N improved grain protein in both winter and spring wheat. Its effects on both yield and grain protein were larger under conventional tillage, in humid climate especially for winter wheat, in coarse textured soils, on less fertile soils, and at high N rate. Splitting N in 3–4 applications would increase annual production of winter wheat by 12.9 M t grain and 1.3 M t protein globally. By identifying the conditions where split N application is more likely to deliver agronomic benefits, our study would contribute to the targeted adoption of this practice. [ABSTRACT FROM AUTHOR]

Abstract: Whereas the concept that availability of resources drives seed production is sound in principle, it is incomplete as there are many solutions to the allocation of resources that derive from the trade-off between number and size. This paper examines evolutionary aspects of this trade-off in annual grain crops. The analysis is centred on the working hypotheses that, for a given species and environment, allocation of resources to reproduction involves (H1) high plasticity in seed number, which allows for variable resource availability, and (H2) a relatively narrow range of seed size that results from evolutionary and agronomic selection. Comparisons between crops and fish are used to highlight common evolutionary elements in taxa where parents provide little or no care to their offspring, with the consequence that both number and early survival of offspring, hence fitness of parents, are partially related to embryo size and reserves. The plasticity of seed number in relation to availability of resources is analysed against the established relationship between offspring number and parent growth rate during critical stages. The notion that seed size is under stabilising selection is analysed against three conditions: (1) mean seed size is conservative for a given species and environment, (2) seed size affects fitness, and (3) seed size is heritable. Databases from published papers were compiled to analyse the relative variability of seed size and number, and the heritability of seed size. Evidence for and against the link between seed size and parental fitness is revised using the Smith–Fretwell model as framework (Am. Nat., 108, 499–506). The proposal of high plasticity of seed number and narrow variability of seed size resulting from stabilising natural selection is generally consistent with evolutionary and genetic considerations. Agronomic selection may have reinforced natural selection leading to relatively narrow seed size in species such as wheat and soybean, where cultivated types retained high plasticity for seed number. In contrast, selection for one or few inflorescences in crops like sunflower and maize may have morphologically reduced seed number plasticity and increased variability of seed size and its responsiveness to resource availability in relation to their wild ancestors. [Copyright &y& Elsevier]

Abstract: A data base including grain yield, nitrogen uptake (N u) and phosphorus uptake (P u) was compiled to investigate the N:P stoichiometry of cereal (n =759), grain legume (n =413) and oilseed species (n =421). Actual ratios and slopes of functions relating nitrogen uptake and phosphorus uptake were used to characterise N:P stoichiometry. The focus is on variability in N:P ratios of field crops, and N:P stoichiometry of crops achieving maximum yield. N:P ratios varied between ∼20, the maximum for legumes and oilseed crops, and ∼1.5, the minimum for cereals. By definition, N:P ratios are a direct function of N uptake and an inverse function of P uptake. The expected association between N:P ratio and N uptake was not evident except for grain legumes whereas the expected relationship between N:P and P uptake was verified for all three crop types. This highlights the role of P uptake as the main source of variability in N:P stoichiometry. The relationship between N uptake (N u) and P uptake (P u) for crops achieving maximum yield in each experiment was markedly non-linear. Functions of the form N u = N max P u/( + P u) described the way in which N:P stoichiometry scaled with grain yield. Maximum uptake of nitrogen (N max) was similar for all three crop types (≈240kgNha−1), but it was achieved via different avenues, i.e. high yield and low grain protein concentration for cereals compared to lower yield and higher grain protein concentration in oilseed and legume crops. Phosphorus uptake at half N max () ranged from 27kgPha−1 for oilseeds to 14kgPha−1 for legumes. The N:P ratio at was 4.5 for oilseed crops, 5.6 for cereals and 8.7 for legumes. For cereals and oilseeds, over 40% of crops attaining maximum yield had N:P ratios in a relatively narrow range between 4 and 6. Variation in grain protein concentration was a major source of instability in N:P ratios of legumes. Being at the base of agro-ecological food webs, the N:P stoichiometry of crops has implications for both decomposers and consumers, and stoichiometric concepts might be of interest in fertiliser management and modelling. Variability in N:P stoichiometry related to plant storage products, however, restricts its application. [Copyright &y& Elsevier]

Clarifying the amount of pest damage that can be tolerated without justifying insecticidal control will be useful in reducing insecticide use and in development of integrated pest management (IPM) systems. This study investigated the ability of irrigated, high-yielding cotton (Gossypium hirsutum L.) to recover from artificially applied damage simulating that of early season insect pests. Six experiments were done across five cotton-growing seasons. Damage included defoliation, terminal damage, and flower bud removal in a range of timings, combinations, and intensities. Crop yield was unaffected by defoliation applied before first flower buds appeared, even when 100% of true leaves were removed on three occasions (Nodes 2, 4, and 6). Crop maturity was affected by sustained high levels of leaf loss with a peak delay of 10 d after 100% defoliation three times. Up to three light tip damage events or one heavy damage event had no effect on yield and only a slight effect on crop maturity (<5-d delay to harvest). Heavy early fruit loss (100% fruit removal from the first four fruiting branches) did not affect yield but caused a delay in maturity of ≈7 d. Equations describing the relationship between damage type, intensity, and repetition and the yield and maturity of cotton were developed and used in sensitivity analysis to define tentative damage thresholds for IPM systems in cotton. [ABSTRACT FROM AUTHOR]

• Modern maize hybrids sown at low densities tiller in non-restrictive environments. • Light quality and plant growth rate at early stages govern tiller emission. • Tiller fertility would be determined by shoot growth rate around flowering. • Reproductive plasticity is needed to stabilize yields in ultra-low density settings. • The impact of tillering on crop water and nitrogen economies is hypothesized. Selection for maize (Zea mays L.) grain yield in high-yielding environments at high population densities has favored a compact phenotype tolerant to crowding stress, bearing a single, well-grained ear. However, by contributing to vegetative and reproductive plasticity (i.e., multiple shoots and ears per plant, respectively), tillering may be adaptive in environments with low and variable availability of resources, chiefly water and nutrients, where crops are sown at low plant population density. In this work we present a robust, new conceptual framework for vegetative and reproductive plasticity in maize with direct agronomic applications, combining original data from new experiments and data reviewed from the literature. First, we describe production systems where tillering in maize would be relevant in terms of grain yield. Next, we discuss possible masked effects of genetic selection at high plant densities on tillering and present novel experimental results showing genotypic variation of tillering in modern maize hybrids and genotype x environment x management effects (plant density x location x sowing date) on tillering expression. We follow with a two-part framework to analyze tillering and prolificacy. In the first part (from axillary buds to tillers), we integrate the early effects of the light environment (through photomorphogenesis) and carbon balance on tillering emission, and discuss the environmental factors (temperature, photoperiod, radiation, water, nitrogen) that modulate tiller emission and tiller growth. In the second part (from tillers to kernels), we summarize the functional relationships governing kernel set on the ears of main shoot (apical and sub-apical ears) and tillers, focusing on the growth rate of shoot cohorts, rather than the whole plant. We then provide examples of the diverse patterns of contribution of multiple shoots to crop grain yield for maize husbandry in low-yielding environments. Finally, we address the effect of tillering on resource capture and use efficiency of maize crops by discussing its relationship with biomass and grain yield and provide supportive experimental data. We conclude with identification of knowledge gaps leading to testable hypotheses. [ABSTRACT FROM AUTHOR]

• We develop a novel method to non-destructively measure crop growth rate in lentil. • Lentil yield correlated non-linearly with crop growth rate. • Lentil yield correlated with biomass and crop growth rate in stressful conditions. • Lentil yield decoupled with biomass and crop growth in higher yielding conditions. • The association of lentil yield and harvest index was significant for all yields. Growth and yield can be decoupled in lentil whereby excessive vegetative growth leads to self-shading, reduced pod and seed set, low harvest index and higher risk of disease and lodging. We evaluated the degree of coupling between growth and yield in 20 lentil lines grown in eight environments varying in water and photothermal conditions returning a 10-fold yield range, from 21 to 221 g m−2. Calibration curves between shoot biomass and canopy cover measured with NDVI and green canopy cover measured with Canopeo app were improved with canopy height as a multiplication factor returning a 3-D trait. Calibration curves were used to phenotype shoot biomass and calculate crop growth rate. For the pooled data, yield correlated non-linearly with crop growth rate, with an x-intercept of 0.09 g m−2 [oCd]-1, suggesting a minimum plant size for reproduction, and an inflection point at 0.43 g m−2 [oCd]-1. Yield correlated with biomass and crop growth rate in the more stressful conditions (yield ≤ 107 g m−2) and was decoupled in higher yielding conditions (yield ≥ 170 g m−2). Yield associated with harvest index at all yield levels, but more strongly in high-yielding conditions. Biomass and harvest index correlated in environments with yield ≤ 107 g m−2, and decoupled under more favourable conditions (yield ≥ 170 g m−2). Yield associated with phenology under stress but not in favourable conditions. For the combination of lines and environments in this study, broad sense heritability was 0.96 for flowering time, 0.93 for harvest index, 0.89 for yield, 0.87 for crop growth rate and 0.39 for biomass. Selection for harvest index would improve yield across environments whereas selection for growth rate could further improve yield under stress. Agronomic practices to improve the coupling of yield and growth under favourable conditions need to be explored; for example, using precision seeding to reduce rectangularity of crop arrangement and favour penetration of radiation into the canopy and pod set. [ABSTRACT FROM AUTHOR]

• Yield gaps for temperature-limited yield potential Y T varied with location, time of sowing, cultivar and nitrogen. • Y T related negatively to mean temperature in the critical period returning a slope of -0.53 t ha−1 °C−1. • Elevated temperature reduced the duration of the critical period and was the largest driver of reduced grain number and yield. • Yield-temperature relationships crossed over in the response to nitrogen fertilisation. Elevated temperature, water deficit, low nitrogen availability and their interactions, constrain wheat yield in Mediterranean-type environments. Our working hypothesis is that, owing to the non-linearity of yield response to water and nitrogen and the non-linearity of biological processes in response to temperature, the outcome of the interactions between temperature, nitrogen and water is range-dependent. To generate a broad range of conditions in testing this hypothesis, we established two experiments. Experiment 1 combined factorially four sowing times, six cultivars and four nitrogen rates in four locations-seasons. Experiment 2 combined factorially two cultivars, two nitrogen rates, and two thermal regimes to further untangle interactions. Thermal regimes were unheated controls, and crops heated with passive open-top heating chambers increasing temperature by 0.5 °C during grain set or grain filling. Across the 384 combinations of treatments in Experiment 1, yield ranged between 0.12 t ha-1 and 5.96 t ha-1. The duration of the critical period (300 °C d before anthesis to 100 °C d after anthesis) decreased with mean temperature at an average rate of 5 d °C-1 and accounted for 75% of the variation in yield. We used quantile regression to calculate a temperature-limited yield potential Y T and derived a linear function between Y T and mean temperature in the critical period, returning a slope of -0.53 t ha-1 °C-1. Yield gap, i.e., the difference between Y T and actual yield, was larger in nitrogen and water-deficient crops. Yield-temperature relationships crossed over in response to nitrogen fertilisation. Fertilised crops (100−200 kg N ha-1) outyielded their unfertilised counterparts when mean temperature during the critical period was below 13 °C, and unfertilised controls were superior above this threshold. Locally calibrated thresholds can be used as a rule-of-thumb adding a further dimension to the management of combined stresses and risk of wheat in Mediterranean-type environments. In Experiment 2, yield responded to the interaction between temperature and nitrogen, whereby elevated temperature during grain set reduced yield by 17% in unfertilised crops with no effect on crops with 100 kg N ha-1. Elevated temperature during grain fill reduced yield by 14% with no effect of nitrogen or nitrogen x temperature interaction on grain yield. [ABSTRACT FROM AUTHOR]