Search

The rate of mycorrhizal colonization in plant roots generally decreases with increased soil nutrient availability but the underlying mechanism is still poorly understood. Our aims were to explore the responses of root mycorrhizal colonization, passage cells, and penetration points under nitrogen (N) and phosphorus (P) addition and their potential linkages in woody and herbaceous plants. N and P were added to the pots of 14 temperate species (eight woody and six herbaceous) in the greenhouse, and the distribution of mycorrhizal colonization, passage cells and penetration points for each species were observed by staining and microscopy of first-order roots. The average density and proportion of mycorrhizal colonization, passage cells and penetration points of 14 species were significantly decreased under N and P addition. The N addition had a stronger effect on the plants than the P addition. More importantly, the mycorrhizal colonization density and proportion showed significant positive correlations with passage cell density and proportion, and with penetration point density and proportion of woody and herbaceous plants under control and nutrient treatments. The density and proportion of mycorrhizal colonization were closely related with passage cells and penetration points in both woody and herbaceous species in either control or nutrient treatments. Our results are of great significance for understanding the relationship between soil fungi and plant roots under changes of soil nutrient availabilities.

In recent decades, temperate herbaceous wetlands have been widely experiencing shrub encroachment. By now, little has been known about whether such alteration in plant community would generate updated soil organic carbon (SOC) conservation strategies, and thus alter SOC dynamics. To assess the temporal dynamics of SOC stock and fractions after shrub encroachment into temperate herbaceous wetlands, we measured floor litter mass, fine root biomass, and SOC stock and fractions (i.e. labile C pool I, labile C pool II, and recalcitrant C pool) across the 0–50 cm soil profile in the open wetlands and shrub islands (Betula fruticose and Salix floderusii) with different basal diameter sizes (small, 10 ~ 15 cm; medium, 15 ~ 20 cm; and large, 20 ~ 30 cm) in the Sanjiang Plain of Northeast China. Regardless of shrub species, SOC stock initially decreased after shrub expansion, but gradually recovered to the initial level of herbaceous wetlands. Moreover, SOC stock correlated positively with fine root biomass, but showed no significant relationship with floor litter mass. The responses of SOC fractions to shrub expansion mainly occurred in the surface soils (0–15 cm), despite a slight change in recalcitrant C pool in 15–50 cm layer. In the surface soils, labile C pool decreased substantially, whereas recalcitrant C pool and recalcitrant index of SOC elevated with increasing shrub sizes. Shrub encroachment can recover SOC pool and enhance SOC recalcitrance in temperate herbaceous wetlands, and altered fine root biomass would account for shrub encroachment-induced SOC dynamics.

The aim of the study was to explore whether the encroachment of an East-African savannah ecosystem by the invasive shrub Dichrostachys cinerea L. Wight & Arn has resulted in changes in the Arbuscular Mycorrhizal Fungus (AMF) communities which are associated with roots of the extant herbaceous plant communities. We hypothesized that this could happen either through introducing new AMF taxa, or through inducing changes in the savannah soil environment or plant community composition. We selected five blocks in the savannah plains of the Nech Sar National Park, southern Ethiopia, and in each block, we established nine vegetation plots along a gradient of D. cinerea encroachment. We sampled roots from the encroaching shrub D. cinerea and from three dominant graminoids (Brachiaria deflexa, Chrysopogon plumulosus, Lintonia nutans) and two forbs (Commelina forskaolii, Ruellia prostrata), and used a metagenomics approach to identify the AMF taxa associated with their roots. D. cinerea exhibited higher AMF richness and diversity, and a significantly different AMF community composition, compared with the sampled herbaceous plants in the unencroached plots. Herbaceous plants in sparsely encroached plots harbored a higher AMF diversity as compared to the control plots, while those in densely encroached plots exhibited an intermediate AMF diversity. D. cinerea encroachment, host plant lifeform, soil characteristics and extant herbaceous plant species diversity all affected AMF community composition associated with the herbaceous plant roots. Woody encroachment might have affected AMF communities of the extant herbaceous vegetation in savannah ecosystems both directly, through introducing novel AMF taxa associated with the encroaching shrub species, and indirectly, through encroachment effects on the environment. Restoration of encroached savannahs should therefore take into account the legacy effects of the invader on the microbial communities.

Water and nitrogen availability are primary determinants of woody communities in dryland ecosystems and are strongly affected by global change. However, the mechanisms by which resource availability and plant demographic responses regulate woody-herb composition are unclear. We investigated plant productivity, shrub demography, and resource availability in a 5-year field experiment involving three levels of precipitation (ambient, + 20% precipitation, + 40% precipitation) and two levels of nitrogen addition (0, 60 kg N ha− 1 yr− 1) in a desert shrubland of northern China. Increased precipitation had similar positive effects on shrub and herbaceous productivity and, thus, did not alter the community composition. However, nitrogen enrichment dramatically increased herbaceous productivity but tended to decrease shrub productivity. Five years after the experimental manipulation, increased precipitation and nitrogen enrichment significantly altered shrub demography. Increased precipitation decreased the number and cover of small shrubs but increased those of large shrubs. Nitrogen enrichment largely decreased the number and cover of small shrubs, whereas large shrubs showed a higher resistance. Structural equation modeling revealed that nitrogen-enhanced herbaceous competition for water and light potentially reduced shrub growth, especially the growth of small shrubs. Our results suggest that large shrubs can coexist with herbs, whereas small shrubs tend to be competitively excluded from the system under enhanced precipitation and nitrogen deposition. Nitrogen enrichment may lead to continued declines in shrub recruitment and growth, and a conversion to grassland. Our findings highlight the competitive and demographic mechanisms underlying the responses of woody communities to global change.

Although leaf and root traits may change considerably throughout plant development, ontogenetic variation is rarely considered in trait-based ecology. Studies focused on how morphological root traits change throughout ontogeny are especially rare. Our objectives were to determine how ontogeny influences seedling traits to inform trait selection for future studies and to advance understanding of how traits at early developmental stages influence seedling growth. We measured traits from eleven herbaceous species at several developmental stages. We used Bayesian random effects models to assess the effects and variation resulting from species identity and ontogeny for each trait. We used principal component analysis and multiple regression to identify which dominant axes of variation were correlated with future growth rates. Variation in traits resulting from ontogeny was greatest for growth rates and root elongation rates. Relationships among traits were similar at all ontogenetic stages, but which principal component axes were correlated with future growth depended on stage; at the earliest harvest, the axis related to tissue construction was linked to future growth rate, whereas, at the last harvest, three independent axes were related to future growth rate. In our study, traits including leaf dry matter content, root tissue density, and root diameter varied little throughout seedling development and thus may be promising candidates for future trait-based studies. Linking suites of traits to growth strategies may be particularly fruitful for understanding plant strategies throughout early development, as multivariate relationships among traits appear to be more ontogenetically stable than individual traits.

Non-additive effects during the decomposition of mixed litter at species level have important consequences on ecosystem nutrient cycling, whereas such effect at plant organ level remains unclear. We investigated mass loss and nutrient release of single and mixed litter from leaf and culm for a dominant grass and of shoots for two dominant grasses under both ambient and enriched N conditions in a temperate grassland. We found comparable mixing effects on litter mass loss and nutrient release at organ and species levels after 2-yr decomposition. Nitrogen enrichment stimulated litter mass loss of all litter types but did not alter the mixing effects on mass loss. Further, N enrichment enhanced the non-additive effects of mixing on N release at plant organ level but not at species level. This study extend the non-additive effects of litter decomposition from inter-specific level to intra-specific level by highlighting the synergistic interaction between leaf litter and culm litter during decomposition. Given the existence of non-additive mixing effects at plant organ level, it is more difficult to predict litter decomposition and nutrient cycling in herbaceous communities.

Changes in snow cover can influence root growth and distribution of herbaceous species in water limiting desert ecosystems. However, how the growth of root systems of herbaceous species responds to snow cover changes remains unclear. Thus, the present study was aimed to examine the influence of snow cover changes on root growth of herbaceous species in a temperate desert of central Asia. Plots with four snow cover depth treatments in winter were investigated in the Gurbantunggut Desert. The four treatments were snow removal (− S), ambient snow, double snow (+ S), and triple snow (+ 2S). We examined the root growth of two typical herbaceous species: one ephemeral species, Erodium oxyrhinchum, and one annual species, Ceratocarpus arenarius. The root length of the annual plant was significantly reduced by snow removal compared with the ambient treatment. The specific root length and specific surface area of the ephemeral plants increased with increasing snow depth, whereas the annual plants showed the opposite trends. Snow removal significantly increased the root–shoot ratio of the annual plants, with no effects found in the ephemeral plants. The individual root biomass and total underground biomass of the two species had similar responses to the snow depth treatments, with the highest values found with the ambient treatment. These results can contribute to explaining to changing winter snow cover depth can alter plant growth, community structure, and ecosystem function in the growing season in temperate desert ecosystems.

Although the linkages between aboveground photosynthates production and belowground respiration processes have been well studied, doubts remain as to the extent that photosynthate regulates soil respiration (Rsoil) and its generality throughout the growing season in a given ecosystem. This study aimed to test whether photosynthesis affected Rsoil at the diurnal scale and assess how the relation between them changed with changing vegetation composition. We measured Rsoil and gross primary productivity (GPP using eddy covariance) in two consecutive growing seasons (2013–2014) in a desert ecosystem, western China. We compared Rsoil on sunny days with that on adjacent cloudy days in two periods with different vegetation compositions [herbs-shrub coexistence period (HSP) and purely shrubs dominated period (SDP)] to identify how photosynthesis affect Rsoil. GPP regulated diurnal variations of Rsoil conspicuously in spite of the strong correlation between soil temperature (Tsoil) and Rsoil, but such regulation was limited in HSP. 48.3% of the changes in daytime Rsoil between sunny and cloudy days was explained by changes in Tsoil together with changes of GPP in HSP. When spring annuals died, no differences in daily amplitude and average of Rsoil between sunny and cloudy days were found. Our results suggested that effect of photosynthesis on Rsoil was not constant throughout the growing season. In the presence of herbaceous plants, Rsoil was directly related to photosynthesis. These findings highlighted the important role of photosynthesis played in Rsoil regulation and the importance of community composition in determining the extent that photosynthesis affects Rsoil.

The positioning of bulbs and stem tubers deep in soil can decrease frost exposure, yet it can come at the cost of increased investment to reach the surface, and delayed emergence. We explored the strength and generality of this trade-off for a range of herbaceous, temperate species. To isolate the direct effects of soil depth on plant growth and survival from the effects of variation in frost exposure, one set of plants buried over winter at three depths experienced either ambient or increased frost (via snow removal), another set sheltered from winter frost stress was buried at three depths in spring, and a third set was exposed to freezing under controlled conditions. Growth generally increased with organ soil depth under increased frost. However, for many species, spring-planted organs exhibited a trade-off of decreased aboveground leaf biomass with greater organ depth. Increased freezing exposure alone generally decreased survival, with sub-lethal effects (particularly decreased leaf biomass) observed for some species. Our results highlight that optimal bud depth is influenced by trade-offs between frost avoidance and plant growth. The balance of this trade-off may shift in coming decades with reduced snow cover and resulting increases in soil frost exposure.

Variations in plant nitrogen (N) and phosphorus (P) concentrations and ratios have great implications for primary productivity and nutrient cycling. Here, we reported their changes at functional group and community levels along an aridity gradient. We carried out a field investigation and set up 26 sampling sites along a transect in the drylands of northern China to examine the responses of plant nutrient status to increasing aridity and the relationships between plant and soil nutrients. The responses of N and P concentrations to increasing aridity differed between woody (sub-) shrubs and herbaceous species (including annual/biennial forbs and grasses, perennial forbs and perennial grasses). Nitrogen and P concentrations of shrubs decreased while those of herbs generally increased with increasing aridity. Plant N:P ratios increased significantly with increasing aridity for the plant functional groups and at the community level. At both organizational levels, nutrient concentrations in plants were negatively related to those in soils. Our results indicated that the responses of plant nutrition to aridity were dependent on plant functional group. Plant growth appeared increasingly limited by P, and plant and soil nutrients become increasingly decoupled at large spatial scale with increasing aridity.

The aim of this study was to cross correlate data on physico-chemical parameters of soil with rhizosphere microorganisms and plant species in order to gain more knowledge about formation of soil and development of plants in the face of the changing climate on Spitsbergen and relations between them. We investigated physico-chemical parameters of soil samples and the number and biodiversity of microorganisms, bacteria (oligotrophic and copiotrophic), and fungi. Moreover, heavy metal concentrations in 6 species of vascular plants collected in different areas were analysed. The soil samples varied considerably in pH – from acid to alkaline, texture – from sand to loamy sand, and C:N ratio – from very low to high. In the soils, only partial Cd elevation expressed as the geoaccumulation index (Igeo) and the enrichment factor (EF) was detected. In the plants, the most significantly elevated concentrations of heavy metals expressed as Igeo and EF as well as the biological accumulation factor, bioconcentration factor, and translocation factor were detected in Salix polaris, Dryas octopetala, and Draba corymbosa. The high number of bacteria corresponded with an increase in the ecophysiological diversity index and the low colony development index, whereas a reverse relationship was found for fungi. There was no significant impact of the geochemical properties on the total content of heavy metals in soil. The similar position of Cd and Pb in the order of heavy metal accumulation in the soil and plants was confirmed. TF showed that mainly these two metals were transported efficiently from roots to shoots. In the plants, the metals were distributed depending on the life form and their higher levels were detected in the woody perennials, e.g. S. polaris, D. octopetala, D. corymbosa, than in the herbaceous perennials. Very high numbers of culturable microorganisms were determined, regardless of the soil properties and plant species, which indicated that they were involved in the transformation of compounds containing C, N, and P and in the availability of heavy metals. The microorganisms and plants colonizing Spitsbergen soils showed great plasticity and adaptability to low temperatures and elevated Cd content.

Disturbance affects the ability of organisms to persist on a site, and disturbance history acts as a filter of community composition. This is true for vascular plants and morphological groups of biocrusts, which respond differently to disturbance. Although functioning arid ecosystems include both groups, filtering of morphological groups of biocrusts has not previously been compared simultaneously with the responses of vascular plants. Using a chronosequence approach, cover of vascular plants and biocrusts was examined across chronic disturbance gradients related to invasion by exotic species and grazing by livestock, following the acute disturbance of fire using paired burned and unburned plots in Wyoming big sagebrush on 99 plots. Cover of vascular plants and biocrusts was related to disturbance more so than abiotic factors of precipitation following fire, soil chemistry, percent coarse fragment and heat load index. Over time since fire of 12–23 years, we saw recovery of early successional groups: short mosses, shallow-rooted perennial grasses and annual forbs. Cover of deep and shallow-rooted perennial grasses and annual forbs increased in cover with intermediate levels of disturbance. Perennial forbs lacked a clear relationship with disturbance. Biocrusts decreased in cover with less disturbance when compared with perennial herbaceous plants but differed in sensitivities. Tall mosses were less sensitive to disturbance compared with lichens. Short mosses increased with some disturbance. Morphological groups of biocrusts and vascular plants are eliminated with increasing variability in the size of gaps between perennials represented by the standard deviation of gaps between perennials. The inclusion of both groups in assessments of ecosystem recovery following disturbance addresses the fact that recovery of either group does not happen in isolation from the other but with interacting contributions to ecosystem functions.

Acid detergent lignin (ADL), acetyl bromide (AcBr), and cupric oxide oxidation (CuO) were compared as methods for determining lignin concentration and quality in plant residues. These three methods were used to analyze 27 plant residues from different groups of species, i.e., legumes, crucifers, herbs, grasses, and trees. Median lignin concentrations of the 27 plant materials were 4.5% ADL and 6.0% AcBr lignin, significantly exceeding the median of 2.1% CuO lignin. ADL concentrations varied from 0.8 to 27.0%; those of AcBr and CuO lignin ranged from 1.8 to 12.2% and from 0.6 to 9.7%, respectively. AcBr lignin showed a significant negative, non-linear relationship with total N. In addition, the relationship of ADL and CuO data was negatively affected by total N. The ADL method is simple and well reproducible, and large datasets are available for comparison. The AcBr procedure is fast, with less interference from non-lignin products than ADL. The CuO method is not interfered with by any other organic component in the plant material and gives additional information on the composition of the lignin. However, the release of phenolic units may be incomplete.

Nitrogen (N) is one of the most important limiting factors influencing plant growth and reproduction in alpine and tundra ecosystems. However, in situ observations of the effects of root traits on N absorption by alpine plant species are still lacking. We investigated the rates of N uptake and the effect of root characteristics in ten common herbaceous alpine plant species using a 15N isotope tracer technique and the root systems of plants growing in a semi-arid steppe environment on the Tibetan Plateau. Our objective was to determine the root traits (root biomass, volume, surface area, average diameter, length, specific root length and specific root area) that make the largest contribution to the total uptake of N (15N–NO3 −, 15N–NH4 + or 15N–glycine) by alpine plant species. Monocotyledonous species had higher absorption rates for 15N–NH4 +, 15N–NO3 −, 15N–glycine and total 15N than dicotyledonous species (P

In most ecosystems, plant roots from different species decompose in mixtures and in the presence of living roots; however much root decomposition research has focused on how roots of individual species or artificial mixtures decompose in the absence of living plants. We thus examined two poorly studied components of root litter decomposition: 1) whether decomposition of root mixtures can be predicted from the sum of the decomposition rates of each component species and 2) how living plants influence rates of root decomposition. Decomposition rates of roots from three perennial herbaceous Mediterranean species grown in monocultures and in two- and three-species mixtures were determined after a one-year incubation period under their living community and in non-vegetated soil (bare soil). Soil respiration in the presence of glucose (substrate induced respiration, SIR) was measured in each plant community and in bare soil. Decomposition rates of root mixtures cannot be predicted from decomposition rates of the component species, both additive and non-additive effects were observed; the presence of low quality roots of Carex humilis in mixtures strongly negatively influenced root decomposition. The presence of living plants stimulated root decomposition in monocultures and two-species communities, likely through an enhanced microbial activity (SIR) under plant communities. This study highlights that root decomposition cannot be predicted from decomposition rates of the component species and is more influenced by endogenous factors or root litter functional composition than by plant community composition.

Long distance signals in xylem from roots to leaves are important in plant response to drought stress. Abscisic acid (ABA) plays a key role in drought signaling in plants but apoplastic pH may modulate its effect by distributing ABA into various compartments in leaves. We aimed to reveal the dynamics of changes in sap pH and its relationships with the transport of inorganic and organic ions in eight herbaceous plant species under continuously declining soil water content. We tested several hypotheses related to the mechanism of pH changes in xylem. We used a pressure chamber to collect xylem sap and to measure of leaf/stem water potential at various stages of soil drying. We measured pH and concentrations of the most abundant inorganic (NO3 −, SO4 2−, PO4 3− and Cl−) and organic (malate and citrate) anions in xylem sap. Species differed considerably in the dynamics of pH changes in xylem in drying soil. Changes in xylem sap pH during drying did not relate to the nitrogen assimilation strategy but may be affected by sap flow rate. Simultaneous changes in the concentrations of inorganic and organic anions were highly species-specific. High variability among species in the observed relationships in response to drought indicates that comparisons among different studies and the generalization of results should be made with caution.

Made available in DSpace on 2018-12-11T16:41:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-03-01 Background and aims: The diverse flora of the Brazilian Cerrado is threatened by agricultural expansion, nutrient enrichment and invasion of alien plants. We performed a fertilization experiment to investigate the nature of nutrient limitation in Cerrado vegetation, and evaluate whether native and alien invasive species are limited by the same or different nutrients. Methods: We applied various combinations of nutrients (phosphorus (P), nitrogen (N), and a mixture of other macro- and micro-nutrients (‘cations treatment’)) to six types of Cerrado vegetation. We then studied over a 3-year period how these treatments affected the aboveground biomass of native forbs, native C3 and C4 grasses, and invasive C4 grasses. Results: The full nutrient treatment (N + P+ ‘cations’) significantly increased total community biomass across our sites, but P alone had no effect. The nutrient treatments also affected the relative abundance of functional plant groups in the six vegetation types. P addition, either alone or in combination with other nutrients, increased the biomass of alien C4 grasses, where present, whereas the cations treatment stimulated growth of the native C4 grasses. Addition of N + P reduced the biomass of native C3 grasses. Conclusions: Our results indicate co-limitation by several nutrients, including P, perhaps N, and at least one other nutrient. Further research is needed to determine what the other nutrient (or nutrients) may be. Native and invasive species appear to be limited by different nutrients, with P alone stimulating growth of African C4 grasses. This should be considered in managing both natural and invaded communities. Institute of Integrative Biology ETH Zürich, Universitätstrasse 16 Departamento de Ecologia Universidade de Brasília, Asa Norte Departamento de Biologia e Zootecnia UNESP – Univ Estadual Paulista, Rua Monção 226 Plant Biology and Nature Management Vrije Universiteit Brussel, Pleinlaan 2 Departamento de Biologia e Zootecnia UNESP – Univ Estadual Paulista, Rua Monção 226

Plant growth and ecosystem processes in semiarid regions are limited by soil nutrient and water availability. Nitrogen (N) and phosphorus (P) status and the N:P ratio alterations among plant organs are critical in understanding the physiology and productivity of the grass-legume mixture system. This study aimed to identify the N and P distribution patterns and N:P stoichiometry of a local grass species mixed with a legume species under varying water and fertilizer supplies. A C4 perennial herbaceous grass Bothriochloa ischaemum and a C3 perennial leguminous subshrub Lespedeza davurica were grown in a pot experiment with a randomized complete block design consisting of four fertilizations (non-NP, +N, +P and +NP fertilizers), three soil water regimes (80, 60 and 40 % of soil water field capacity, FC) and six planting ratios (2:10, 4:8, 6:6, 8:4, 10:2, and 12:0, grass:legume plants, respectively). Plants were assessed for biomass production, N and P concentration and N:P ratios in various organs 202 days after sowing (DAS). For the grass species (B. ischaemum), N and P concentrations of leaf, stem and root were higher when mixed with the legume (L. davurica) compared to its monoculture, and with a trend to decrease as its mixture proportion increased. Supply with P fertilizer (+P) increased N and P concentrations of B. ischaemum regardless of mixture proportions and soil water regimes. In mixtures, N concentration was the highest in the root system followed by the leaf, and the least in the stem. There was no significant difference in N:P ratio of the stem and the root across the mixture proportions under +P and +NP treatments, and among all soil water regimes, either. Root N:P ratio was significantly lower under +P and +NP than that under non-NP or +N treatment regardless of mixture proportions and soil water regimes. N and P capture and absorption in B. ischaemum were greatly improved when mixed with the legume species, L. davurica. The N and P concentrations in different organs were influenced by both fertilization and the mixture proportions. Application with combined N and P fertilizers enhanced N and P uptake in B. ischaemum. P fertilization should be considered when establishing artificial grassland using native species in the region.

Desert herbs, a crucial component of desert ecosystems, are sensitive to water and nutrient availability and therefore to environmental change. We aimed to determine element concentrations in desert herbs and their relationships with life form, taxonomy, climate, and soil environment. We measured concentrations of 11 elements in shoots and roots of 26 dominant desert herb species from 45 sites in a temperate desert. Shoots of desert herbs had greater concentrations of elements related to photosynthesis and water use efficiency (N, P, Mg, K) than roots. Concentrations of these elements (except N and P) were also greater in annual herbs than in perennial herbs. Greater Mg, K, and Na concentrations were observed in shoots of Chenopodiaceae (mostly C4 species) than in Poaceae (mostly C3 species). Soil properties and taxonomy explained 3.6–26 % and 2.8–24 % of the variation in shoot element concentrations, respectively, whereas climate factors explained only 0.05–6.5 % of the variation. Water and nutrient availability, which are affected by environmental change, influence concentrations of mineral elements in desert plants and their biogeochemical cycles in desert ecosystems.

The variability patterns of fern root characteristics have seldom been studied. Here we explored variability in root morphology, histology and chemistry among fern species of temperate forest, and compared the observed patterns with those of seed plants. We sampled nine herbaceous fern species from temperate forest in northeastern China, and measured root morphological, histological and chemical characteristics across branch orders for each species. All nine fern species had 3 or 4 root orders. With increasing root order, diameter, tissue density, cortical thickness and vascular cylinder diameter increased, while specific root length (SRL) and tissue nitrogen concentration decreased. These were similar to the variability patterns that have been reported for seed plants, except for cortex. Like seed plants, nine fern species showed close relationships among root morphological, histological and chemical characteristics in first-order roots, such as diameter and cortex, tissue density and nitrogen concentration, suggesting that the general linkage between root structure and function exists in all vascular plants. The observed variation within fern root systems is comparable to the reported variation in seed plants, indicating that the same functional constraints control the evolution and development of root systems in vascular plants belonging either to the fern or seed plant lineages.

Background and aims The South African herbaceous legume species Lessertia capitata, L. diffusa, L. excisa L. incana and L. herbacea were introduced to Australia to assess plant establishment and survival, as well as the saprophytic ability of their root nodule bacteria (RNB). Methods Five Lessertia spp., were inoculated with selected RNB strains and were sown in five different agroclimatic areas of the Western Australian wheatbelt during 2007 and 2008. Plant population and summer survival were evaluated in situ. Soil samples and nodules from host plants were also taken from each site. The re-isolated rhizobia were RPO1-PCR fingerprinted and their partial dnaK and nodA genes were sequenced to confirm their identity. Results Plants achieved only poor establishment followed by weak summer survival. More than 83 % of the rhizobia re-isolated from Lessertia did not correlate with the original inoculants’ fingerprints, and were identified as Rhizobium leguminosarum. The nodA sequences of the naturalised strains were also

Salt stress is an increasing problem in agricultural soils in many parts of the world, and salt tolerant cropping systems are in great demand. We investigated the effect of co-inoculation of Galega officinalis with Rhizobium galegae and two plant growth promoting Pseudomonas species on plant growth, nodulation, and N content under salt stress. The effect of inoculation with R. galegae sv. officinalis HAMBI 1141 alone and in combination with the root-colonizing Pseudomonas extremorientalis TSAU20 or Pseudomonas trivialis 3Re27 on the growth of G. officinalis exposed to salt stress (50 and 75 mM NaCl) was studied under gnotobiotic and greenhouse conditions. The growth of goat’s rue was reduced at 50 and 75 mM NaCl both in the gnotobiotic sand system and in low-fertilized potting soil in the greenhouse. Co-inoculation of unstressed and salt-stressed goat’s rue with R. galegae HAMBI 1141 and either P. extremorientalis TSAU20 or P. trivialis 3Re27 significantly improved root and shoot growth and increased nodulation of plant roots in both growth systems compared with plants inoculated with R. galegae alone. The nitrogen content of co-inoculated plant roots was significantly increased at 75 mM NaCl in potting soil. Co-inoculation of G. officinalis with either of the two plant growth promoting (PGPR) Pseudomonas strains also improved root tip-colonization by R. galegae cells. The co-inoculation of goat’s rue with Rhizobium and PGPR Pseudomonas strains alleviated salt stress of plants grown in NaCl-amended gnotobiotic sand systems and in potting soil in the greenhouse.

Aims Bacteria possessing ACC deaminase activity reduce the level of stress ethylene conferring resistance and stimulating growth of plants under various biotic and abiotic stresses. The present study aims at isolating efficient ACC deaminase producing PGPR strains from the rhizosphere of rice plants grown in coastal saline soils and quantifying the effect of potent PGPR isolates on rice seed germination and seedling growth under salinity stress and ethylene production from rice seedlings inoculated with ACC deaminase containing PGPR.

The beneficial effects of Si have mainly been observed in herbaceous plants, while little is known about its role in deciduous trees. The aim of this work was to evaluate the effect of foliar application of Si on chestnut leaf growth, photosynthesis and water relations in the presence of short, but intense water deficit. Sili-K® solution (containing 0.12 % Si and 0.15 % K) was repeatedly (× 3) sprayed onto leaves of potted chestnut plantlets and irrigation was suspended 7 weeks later, for 8 days. Leaf growth, anatomy, as well as physiological and biochemical traits of the plantlets were studied. Si application enhanced chestnut growth, due to increased photosynthetic traits, including higher chlorophyll content and chlorophyll a to b ratio, photochemical efficiency of PSII, gas exchange (stomatal conductance, transpiration rate, net CO2 assimilation) and oxygen evolution rate. Meanwhile, Si yielded larger and thinner leaves, higher xylem, specific leaf area and transpiration rate, thus being beneficial to the tree in absorbing sunlight energy for photosynthesis and in alleviating heat stress. However, Si also lowered leaf sap osmotic pressure, causing the plant to lose water more quickly, thus being more susceptible to water stress. Si improved chestnut photosynthesis, growth, and heat stress tolerance, but it also increased the susceptibility to drought.

Australian herbaceous native species have evolved in phosphorus (P) impoverished soils. Our objective was to explore shoot and root adaptations of two of these species with potential to be developed as pasture plants, at low, moderate and high P supply after 4 and 7 weeks of growth. A glasshouse experiment examined the effect of 5, 20 and 80 mg P kg−1 air-dry soil on growth, rhizosphere carboxylate content, and mineral nutrition of two Australian native perennials, Kennedia nigricans (Fabaceae) and Ptilotus polystachyus (Amaranthaceae), and the exotic Medicago sativa (Fabaceae). Leaf P concentrations at P80 were 6, 14 and 52 mg P g−1 leaf dry weight for M. sativa, K. nigricans and P. polystachyus, respectively. As soil P concentration increased, rhizosphere carboxylate content decreased for M. sativa, increased and then decreased for K. nigricans and was unchanged for P. polystachyus. For all species, the contribution of malic acid declined at the second harvest. For all species and P treatments, the amount of rhizosphere carboxylates per unit root length decreased as root length of a plant increased. Plant P content was determined more by P uptake rate per unit root length and time than by root length. Uptake of Mo for all species, and uptake of K, Mg and Mn for P. polystachyus, increased with soil P concentration. Uptake of Fe and S was higher when the content of carboxylates in the rhizosphere was higher. Root physiological adaptations (i.e. rhizosphere carboxylate content and P-uptake rate) are more important than morphological adaptations (i.e. root length and diameter) to enhance the uptake of P and cations.

Although changes in water and nitrogen (N) supply have been largely used to explain modifications in plant communities, the spatio-temporal variability of those factors has been little studied in chalky environments. In this study, we explored for 1 year the temporal variations in soil water content, N inorganic forms and net N-mineralization and nitrification for two horizons in three herbaceous communities (short grasslands, tall grasslands, and encroached grasslands) in the Henouville Nature Reserve (Upper-Normandy, France). Plant available soil water and permanent wilting points of seven plant species were also characterized. We found that plant available soil water was lower in short grasslands than in tall grasslands and encroached grasslands. Soil water content was below permanent wilting point during four months in short grasslands and only three months in the other communities. Seasonal patterns for inorganic N content and N-mineralization and nitrification were observed with peaks of NH 4 + –N in summer and peaks of N-mineralization in spring. For the studied year, our data highlight the harsh soil desiccation that vegetation endured during the late spring (active growth period) and summer, and show that water shortage is an ecological factor affecting the N cycling in the three successional herbaceous communities.

Introduction The measurement of electrical capacitance across a root system has been proposed as a quick, affordable, non-invasive and non-destructive method to estimate plant root biomass. Few studies have evaluated this method and of these, most have used plants grown either in hydroponic or sand-based growth media. Our objective was to determine if measures of root electrical capacitance can provide accurate estimates the root biomass of plants grown in soil.

Aims In the present study, we analysed the diversity of indigenous arbuscular mycorrhizal fungi (AMF) colonising both the roots and rhizosphere soil of an annual herbaceous species, Bromus rubens, and a perennial herbaceous species, Brachypodium retusum, co-occurring in the same Mediterranean, semiarid degraded area. The intention was to study whether these two species promoted the diversity of AM fungi in their rhizospheres differently and to ascertain whether the AMF community harboured by an annual plant species differed from that harboured by a perennial species when both grew in the same place.

Plant species differ in their capacity to use nonexchangeable potassium (NEK) in soils. In this study two typical plants with high K use efficiency, ryegrass and grain amaranth, were compared with regard to their capacity to use K from five K-bearing minerals. Biomass relative yield and K uptake data indicated that ryegrass was much more efficient than grain amaranth at using NEK in minerals. Root exudates of grain amaranth collected under hydroponic culture contained considerable amounts of oxalic and citric acids, while these acids were not detected in ryegrass root exudates. Compared with grain amaranth, the kinetic parameters of K uptake by ryegrass roots were characterized by a significantly higher K uptake rate (Vmax) and a significantly lower Cmin, the minimum external K concentration at which K is taken up. The dynamic release of NEK from minerals in various solutions showed that the release rate of NEK was largely K-concentration dependent and some thresholds of K concentration prevented further NEK release from minerals. The K thresholds were related to mineral type and increased in the presence of Ca2+ or Na+ in solutions. The positive effect of H+ (20 mmol L−1) on NEK release was also mainly attributed to elevating the thresholds of K concentration, rather than to the effects of weathering. The results indicated that the main mechanism by which plant species efficiently use NEK in minerals was to the capacity of plants to absorb K at low concentrations. The lower the Cmin for the root K uptake, the higher the expected NEK use efficiency of the plant.

Although the link between leaf mass loss and assessment of ecosystem nutrient use efficiency and plant nutrient resorption efficiency has received considerable attention in various ecosystems, there has been relatively little effort to assess plant leaf mass loss during senescence, especially for herbaceous species. We conducted experimental studies to assess leaf mass loss during senescence in five dominant herbaceous species and examined the effects of increasing nitrogen (N) and water availability on leaf mass loss of four species in a temperate steppe in northern China. We nondestructively estimated mature leaf mass based on leaf length and width. Leaf mass loss varied substan- tiallyamongspecies,rangingfrom20-50%.Onaverage across all species, N and water addition increased leaf mass loss by 30% and 19%, respectively. N and water addition interacted to affect leaf mass loss, as water addition had a significant positive effect on leaf mass loss under enriched N conditions but showed no effect under ambient N levels. We conclude that leaf mass loss of herbaceous plants was considerable and can poten- tially be more pronounced with increasing N and water availability. It is notable that the responses of plant species to N and water addition were variable. We suggest that leaf mass loss during senescence should be given full consideration in assessing nutrient use and resorption efficiency in semi-arid areas.

Change in morphological and physiological parameters in response to phosphorus (P) supply was studied in 11 perennial herbaceous legume species, six Australian native (Lotus australis, Cullen australasicum, Kennedia prorepens, K. prostrata, Glycine canescens, C. tenax) and five exotic species (Medicago sativa, Lotononis bainesii, Bituminaria bituminosa var albomarginata, Lotus corniculatus, Macroptilium bracteatum). We aimed to identify mechanisms for P acquisition from soil. Plants were grown in sterilised washed river sand; eight levels of P as KH2PO4 ranging from 0 to 384 μg P g−1 soil were applied. Plant growth under low-P conditions strongly correlated with physiological P-use efficiency and/or P-uptake efficiency. Taking all species together, at 6 μg P g−1 soil there was a good correlation between P uptake and both root surface area and total root length. All species had higher amounts of carboxylates in the rhizosphere under a low level of P application. Six of the 11 species increased the fraction of rhizosphere citrate in response to low P, which was accompanied by a reduction in malonate, except L. corniculatus. In addition, species showed different plasticity in response to P-application levels and different strategies in response to P deficiency. Our results show that many of the 11 species have prospects for low-input agroecosystems based on their high P-uptake and P-use efficiency.

Seasonal variation of arbuscular mycorrhizal fungi (AMF) in roots of the high salt marsh plant Spartina patens, the diversity of nitrogen-fixing bacteria in the rhizosphere and plant growth performance was studied at key stages of the growing season coinciding with major plant phenological stages, i.e., vegetative growth, reproduction and senescence. AMF colonization was highest during vegetative growth, with values declining during the growing season to the same level seen at plant dormancy. AMF colonization was reduced at lower depths in the sediments where anoxic conditions were observed and in plants treated with the systemic fungicide Benomyl. Only small changes in diversity of nitrogen-fixing bacteria in general and more specifically of those belonging to the e-subdivision of Proteobacteria were detected during the season or between treatments by PCR-RFLP of nifH gene fragments with DNA as template for amplification; however, greater seasonal changes were displayed when cDNA was used as template for amplification as a proxy for gene expression and thus active bacteria. DGGE analyses of nifH gene fragments representing nitrogen-fixing bacteria of the e-subdivision of Proteobacteria using both using DNA and cDNA as template showed highly diverse profiles that changed during the season and in response to treatment. Seasonal changes were observed for a suite of plant growth attributes and differences were observed between treatments, with higher values generally obtained on non-treated plants compared to Benomyl-treated plants. These differences were most pronounced during vegetative growth; however, differences between non-treated and Benomyl-treated plants were reduced seasonally and disappeared by the onset of senescence. This study demonstrates seasonal changes in AMF colonization on S. patens and in the community structure of nitrogen-fixing members of the e-subdivision of Proteobacteria in the plant root zone. Plant growth performance changed seasonally with some effects of Benomyl-treatment.

This paper focuses on the causes of zonation on agricultural land affected by secondary salinity between two halophytic grasses, puccinellia (Puccinellia ciliata Bor. cv. Menemen) and tall wheatgrass (Thinopyrum ponticum (Podp.) Z.-W. Liu & R.R.-C. Wang cv. Tyrrell). We hypothesized that the differences in zonation of puccinellia and tall wheatgrass were caused primarily by differences in the tolerance of these two species to waterlogging under saline conditions. This hypothesis was tested by conducting experiments in the field and in the glasshouse in irrigated sand cultures. At a saltland field site, locations dominated by puccinellia had ECe values that were consistently higher (11–12 dS/m in early spring, and 5–9 dS/m in late summer) than locations dominated by tall wheatgrass. However locations dominated by puccinellia also had a watertable that was shallower (0.07–0.09 m in the high rainfall season; 0.11–0.13 m in the low rainfall season) than locations dominated by tall wheatgrass. In the glasshouse both species had similar growth responses to salinity under drained conditions, with a 50% decrease in shoot dry mass (DM) at ∼300 mM NaCl. However, the combination of salinity (250 mM NaCl) and waterlogging increased puccinellia shoot DM by 150% but decreased shoot DM of tall wheatgrass by 90% (compared with salinity alone). Under saline/waterlogged conditions, puccinellia showed better exclusion of Na+ and maintenance of K+/Na+ in the shoots than tall wheatgrass. We conclude that the zonation of puccinellia and tall wheatgrass is associated with differences in their ion regulation which leads to substantial differences in their growth under saline/waterlogged conditions.

Brachiaria forage grasses are widely used for livestock production in the tropics. Signalgrass (Brachiaria decumbens cv. Basilisk, CIAT 606) is better adapted to low phosphorus (P) soils than ruzigrass (B. ruziziensis cv. Kennedy, CIAT 654), but the physiological basis of differences in low-P adaptation is unknown. We characterized morphological and physiological responses of signalgrass and ruzigrass to low P supply by growing both grasses for 30 days in nutrient solution with two levels of P supply using the hydroxyapatite pouch system. Ruzigrass produced more biomass at both levels of P supply whilst signalgrass appears to be a slower-growing grass. Both grasses increased biomass allocation to roots and had higher root acid phosphatase and phytase activities at low P supply. At low P supply, ruzigrass showed greater morphological plasticity as its leaf mass density and lateral root fraction increased. For signalgrass, morphological traits that are not responsive to variation in P supply might confer long-term ecological advantages contributing to its superior field persistence: greater shoot tissue mass density (dry matter content) might lower nutrient requirements while maintenance of lateral root growth might be important for nutrient acquisition in patchy soils. Physiological plasticity in nutrient partitioning between root classes was also evident for signalgrass as main roots had higher nutrient concentrations at high P supply. Our results highlight the importance of analyzing morphological and physiological trait profiles and determining the role of phenotypic plasticity to characterize differences in low-P adaptation between Brachiaria genotypes.

Graminoids and forbs are important entities in grassland community assembly, differing in their functional properties. In our study, we asked 1. Do graminoids and forbs differ in the speed of root proliferation into soil patches established under field conditions? 2. Is the patch occupation dynamics affected by the nutrient concentration in the patch? 3. What is the temporal dynamics of available macronutrients in an experimental patch and does it provide comparative advantage to any of these two categories in connection with their root proliferation dynamics? We used ingrowth core technique. Proliferated roots were sampled after 1, 2, 4, 8, or 15 weeks, with forb and graminoid categories distinguished on anatomical basis. We measured root length and root dry weight, concentration of NH4+, NO3−, and of exchangeable phosphorus in the soil. Roots of both functional groups proliferated more intensively in enriched soil patches than in the control ones, but graminoids entered experimental patches more rapidly. Soil concetration of available N fell down to the background level in four weeks. The initial head start by graminoids seems to be crucial for the overall patch exploitation, because the concentration of available nutrient forms, namely nitrate and ammonium, decreases rapidly.

Phosphorus (P) deficiency is a major problem for Australian agriculture. Development of new perennial pasture legumes that acquire or use P more efficiently than the current major perennial pasture legume, lucerne (Medicago sativa L.), is urgent. A glasshouse experiment compared the response of ten perennial herbaceous legume species to a series of P supplies ranging from 0 to 384 µg g−1 soil, with lucerne as the control. Under low-P conditions, several legumes produced more biomass than lucerne. Four species (Lotononis bainesii Baker, Kennedia prorepens F.Muell, K. prostrata R.Br, Bituminaria bituminosa (L.) C.H.Stirt) achieved maximum growth at 12 µg P g−1 soil, while other species required 24 µg P g−1. In most tested legumes, biomass production was reduced when P supply was ≥192 µg g−1, due to P toxicity, while L. bainesii and K. prorepens showed reduced biomass when P was ≥24 µg g−1 and K. prostrata at ≥48 µg P g−1 soil. B. bituminosa and Glycine canescens F.J.Herm required less soil P to achieve 0.5 g dry mass than the other species did. Lucerne performed poorly with low P supply and our results suggest that some novel perennial legumes may perform better on low-P soils.

Excess aluminum (Al) ions and phosphorus (P) deficiency are the key factors that limit plant growth in acid soils. Secretion of organic acids (OA) from roots has been proposed as an Al-resistance mechanism. Nonetheless, the correlation between Al resistance and this mechanism has not been tested beyond a very small number of Al-resistant and Al-sensitive genotypes. To elucidate the mechanisms responsible for plant adaptability to acid soils, we studied the secretion of OA from roots of Stylosanthes in response to high-Al and low-P stresses using six different genotypes. Relative root inhibition by 50 µM Al ranged from 25–71% and differed significantly among six Stylosanthes genotypes. Al treatment induced the secretion of citrate from the roots of Stylosanthes seedling in a dose- and time-dependent manner. Moreover, the secretion rate was significantly higher in the Al-resistant genotype. On the other hand, inhibition of Al-induced citrate secretion by phenylisothiocyanate or 9-anthracenecarboxylic acid resulted in an increase in Al content in Stylosanthes root apices. P deficiency also induced citrate secretion from Stylosanthes seedling roots. Furthermore, citrate secretion was much more robust with exposure to both excess-Al and P-deficiency stresses than under either stress alone. Unlike Al-induced citrate secretion, which was rapid, low-P-induced secretion was a slow process, with significant increases in secretion only becoming evident after 6 d of treatment with free phosphate. The lag between treatment with Al and citrate secretion was approximately 4 h. These results suggest that the secretion of citrate is a mechanism for resistance to both excess-Al and low-P stresses in Stylosanthes.

Assessing natural variability of leaf water use efficiency in plants adapted to extreme conditions of the Mediterranean climate represents an important step in the evaluation of the usefulness of some plant ecophysiological traits under water stress. Eleven Mediterranean species naturally inhabiting the Balearic Islands and corresponding to different growth forms (herbs, semi-deciduous shrubs, woody evergreen shrubs and woody evergreen semi-shrubs) were subject to progressive soil water depletion. Leaf intrinsic water use efficiency was measured by gas exchange at four different degrees of water stress. Under well watered conditions, differences in leaf intrinsic water use efficiency (A N/g s) among growth forms were limited to woody evergreen semi-shrubs, which presented the highest values. Under water stress conditions, differences became more evident, with a trend for an increase in A N/g s from woody evergreen shrubs, through semi-deciduous shrubs and herbaceous to woody evergreen semi-shrubs. The observed variation in A N/g s correlated with several physiological (leaf water potential, soil to leaf hydraulic conductance and stomatal conductance) and morphological (stomatal density) parameters, displaying a general relationship for all growth forms. This suggests that the capacity for withstanding water limitation is adaptive for all Mediterranean species. However, when A N/g s was related to leaf mass area, this relationship was not generally applicable, and depended on growth forms, suggesting that different growth forms display specific morphological adjustments in response to water shortage.

Though the affinity of iron oxides and hydroxides for phosphorus (P) is thought to limit growth and productivity of plants on iron-rich acidic soils in humid tropical climate, tall trees are found in tropical rainforests, and vigorous growth occurs in herbaceous vegetation in the humid tropical climate of the Andamans. Our study reports how high rainfall influences Bray and Kurtz P-1 extractable P, water filled pore space (WFPS), microbial biomass carbon (MB-C) and phosphorus (MB-P) in the gravelly-sandy-loamy soils in three major land use systems: moist-evergreen forest, semi-evergreen forest and homegarden, in the equatorial humid tropical climate of South Andaman island of India. In addition, an ex-situ experiment investigated how labile carbon (glucose) under different soil-water regimes [25% field capacity (FC) and 100% FC] affected the P in the soils under the land use systems. WFPS, across the land use systems, was more than two times higher during the high rainfall than dry spell (72–80 hr after the high rainfall). The extractable P, across the land use systems, increased about 5 to 6 fold during the high rainfall than dry spell. The increase was the highest in the homegarden and lowest in moist-evergreen forest. The extractable P was positively correlated with the WFPS. MB-C and MB-P were lower during the high rainfall than dry spell in all the land use systems. In the ex-situ experiment, the extractable P increased 1.4 to 1.7 fold more in water (100% FC) + glucose than water (100% FC) alone treatment. Water at 25% FC did not increase the extractable P in the soils under all the land use systems. After cessation of the high rainfall, WFPS declined quickly within 2-hr in the upper layer (0–5 cm) of the soils. These indicate that the high rainfall together with labile carbon increases the extractable P through anaerobiosis, whereas, quick decline in the WFPS (0–5 cm) following cessation of the high rainfall helps its uptake by plants and microflora.

This study examines whether root traits differed between three major plant families (Asteraceae, Fabaceae and Poaceae) and whether they are related to root respiration and exudation. Nine traits related to biomass allocation, root topology, morphology, chemical composition and mycorrhizal colonisation were examined for nine C3 herbaceous species grown in controlled conditions. Poaceae differed from Fabaceae for the whole set of root traits examined except mycorrhizal colonisation, while Asteraceae showed intermediate characteristics. As compared to Fabaceae, Poaceae allocated more biomass to roots; showed a more sparsely branched root system with a small average root diameter, a high root dry matter content and a low nitrogen concentration. Root respiration was weakly related to root mass ratio and root dry matter content; no significant relationship was found between root functions and root architecture or morphology. This study shows that plant classification based on taxonomic affiliation reflects differences in root system traits and functions. Whole root system traits do not allow strong predictions of root respiration and exudation, perhaps because these processes are more linked to fine root than to whole root system traits.

The banana (Musa sp.) plant is one of the largest monocotyledoneous terrestrial herbaceous plants in the world. The measurement of transpiration (Tr) for a whole banana plant is always difficult to perform due to its size. However, the sap flow (SF) of the plant has been successfully measured by using the thermal dissipation probe (TDP) or ‘Granier’ method in the corm of the banana plant (Lu et al. J Exp Bot 53:1771–1779, 2002). The present study aimed to validate their method using a sizable number of banana plants in a greenhouse in Israel. The SF data was compared to the gravimetric measurement of transpiration. The lag time of SF behind Tr was also analyzed. Results showed that the daily SF agreed with the daily Tr when the effective radius for sap flow in the corm was taken as 0.63 R, where R is the radius of the corm. The SF lagged 45 min behind the Tr from 0630 to 1040 hours. Whereas the Tr was not statistically (P>0.05) different from the SF between 1330 and 1700 hours. The reduction in water capacity of banana plant due to SF lag was about 10.5% of the daily Tr, and it recovered gradually in the afternoon. Using more plants can reduce the measurement error of the TDP method. The measured daily SF can be considered as an accurate estimation of the daily Tr for banana plant.

A number of studies have tested the effect of woody and herbaceous legumes on soil fertility and maize yields in sub-Saharan Africa. However, their effects on maize productivity are much debated because results have been variable. A meta-analysis was conducted with the aim of evaluating the evidence in support of yield benefits from woody and herbaceous green manure legumes. A total of 94 peer-reviewed publications from West, East and southern Africa qualified for inclusion in the analysis. Maize yield from herbaceous green manure legumes (54 publications), non-coppicing legumes (48 publications), coppicing woody legumes (10 publications), natural fallows (29 publications), and fully fertilized monoculture maize (52 publications) were compared. Mixed linear modelling using yield differences (D) and response ratios (RR) indicated that the response to legumes is positive. The mean yield increase (D) over unfertilized maize was highest (2.3 t ha−1) and least variable (CV = 70%) in fully fertilized maize, while it was lowest (0.3 t ha−1) and most variable (CV = 229%) in natural fallows. The increase in yield over unfertilized maize was 1.6 t ha−1 with coppicing woody legumes, 1.3 t ha−1 with non-coppicing woody legumes and 0.8 t ha-1 with herbaceous green manure legumes. Doubling and tripling of yields relative to the control (RR > 2) was recorded in coppicing species (67% of the cases), non-coppicing legumes (45% of the cases), herbaceous green manure legumes (16% of the cases) and natural fallows (19% of the cases). However, doubling or tripling of yields occurred only in low and medium potential sites. Amending post-fallow plots with 50% of the recommended fertilizer dose further increased yields by over 25% indicating that legume rotations may play an important role in reducing fertilizer requirements. Except with the natural fallow, the 95% confidence intervals of D and RR were higher than 1 and 0, respectively indicating significant and positive response to treatments. Therefore, it is concluded that the global maize yield response to legumes is significantly positive and higher than unfertilized maize and natural vegetation fallows.

This study assessed the suitability of two deciduous woody perennials (Salix spp. and Populus spp.) and two summer green herbaceous perennials (Phragmites australis and Urtica dioica) for purification of nutrient enriched wastewater. The main hypothesis tested was that species with a particular trait combination of high relative growth rate (RGR), low nutrient productivity (A) and high mean residence time (MRT) of nutrients would be most effective in accumulating nutrients. The nitrogen and phosphorus use efficiency at the whole plant level was analysed. Four treatments comprising two possible phytoremediation substrates (municipal wastewater and landfill leachate) and two control plant nutrition situations (balanced nutrient solution and pure water) were applied in four replications to the four plant species. Generally, all four species studied showed a high RGR and a low P productivity in the balanced nutrient solution treatment, while the opposite (low RGR and high P productivity) was seen in the phytoremediation substrate and pure water treatments. The general conclusion is that if P is present in marginal proportions in the wastewater, a vegetation filter with Phragmites would have an advantage since biomass and nutrient accumulation in Phragmites does not decrease as much during phytoremediation as that in deciduous woody perennials.

Plant–insect interactions can alter ecosystem processes, especially if the insects modify plant architecture, quality, or the quantity of leaf litter inputs. In this study, we investigated the interactions between the rosette gall midge Rhopalomyia solidaginis and tall goldenrod, Solidago altissima, to quantify the degree to which the midge alters plant architecture and how the galls affect rates of litter decomposition and nutrient release in an old-field ecosystem. R. solidaginis commonly leads to the formation of a distinct apical rosette gall on S. altissima and approximately 15% of the ramets in a S. altissima patch were galled (range: 3–34%). Aboveground biomass of galled ramets was 60% higher and the leaf area density was four times greater on galled leaf tissue relative to the portions of the plant that were not affected by the gall. Overall decomposition rate constants did not differ between galled and ungalled leaf litter. However, leaf-litter mass loss was lower in galled litter relative to ungalled litter, which was likely driven by modest differences in initial litter chemistry; this effect diminished after 12 weeks of decomposition in the field. The proportion of N remaining was always higher in galled litter than in ungalled litter at each collection date indicating differential release of nitrogen in galled leaf litter. Several studies have shown that plant–insect interactions on woody species can alter ecosystem processes by affecting the quality or quantity of litter inputs. Our results illustrate how plant–insect interactions in an herbaceous species can affect ecosystem processes by altering the quality and quantity of litter inputs. Given that S. altissima dominates fields and that R. solidaginis galls are highly abundant throughout eastern North America, these interactions are likely to be important for both the structure and function of old-field ecosystems.

Resource competition and chemical interference are mechanisms of interaction among plants that may occur simultaneously. However, both mechanisms are rarely considered together when modelling plant growth. We propose a new empirical model that estimates biologically significant parameters on both plant competition and chemical interference. The model is tested with data sets from different density-dependent experiments done with two species (the grass Lolium rigidum Gaud. and the legume Glycine max soya L.) subjected to a noxious chemical environment when growing (allelochemicals and herbicides, respectively). Hypotheses on the effect of allelochemicals and its interaction with density are tested using maximum likelihood ratio tests in order to ask, for these species, whether chemical interference is playing a significant role in the interactions among plants or on the contrary, whether interactions among plants are sufficiently explained by the resource competition. In all cases a significant interaction between chemicals and density is observed. This interaction is inconsistent with the hypothesis of only resource competition having an influence of plant biomass and suggests a significant density-dependent effect of chemicals on plant growth.

The increase in concentrations of phenolic compounds in boron (B) deficiency has been demonstrated in many herbaceous plant species, but information on woody plants is scarce. It has been suggested that accumulation of phenolic compounds plays a role in the development of cold hardiness in herbaceous plants but also that B deficiency decreases winter hardiness. Here we study the effects of B nutrition on phenolic compounds in Norway spruce (Picea abies L.) in the course of cold acclimation. Phenolic compounds were analysed in Norway spruce seedlings from three different B-fertilisation treatments in two harvests: non-acclimated and cold-acclimated seedlings. Norway spruce phenolic compounds consisted mainly of condensed tannins. During B deficiency, condensed tannins and monocoumaroyl–astragalin der. 1 increased in non-acclimated seedlings. The increase in tannins was 21%, which was nearly significant. However, the effect of B on phenolic compounds was almost absent in cold-acclimated seedlings. The condensed tannin concentration increased much more with time in the simulated autumn than due to B deficiency, and we conclude that the B effect was probably not large enough to be important for the hardening of the seedlings. The total phenolic concentrations more than doubled during the course of cold hardening suggesting that phenolics have a role in the winter hardiness in Norway spruce.

The response of introduced (Pennisetum clandestinum Hochst.) and native (Stipa aristiglumis F. Muell., Themeda australis (R. Br.) Stapf, Danthonia spp. (L.) grasses to the herbicide atrazine was studied in plants with the potential for use in vegetated filters (biofilters) designed to reduce chemical loads in agricultural runoff. The response was detected by photosynthetic inhibition using leaf chlorophyll fluorescence. With continuous short-term (14 days) dosing with atrazine in sand culture, P. clandestinum showed the greatest tolerance, regardless of the dose (20–500 μg/L). In a clay vertosol soil in the glasshouse, the four species were tolerant to longer-term (84 days) application of three successive doses of simulated run-on, each dose containing 100 μg/L atrazine, a concentration which is comparable to the highest reported in runoff from agricultural land in Australia. Even with a subsequent single atrazine dose at ∼ ∼5000 μg/L, established plants of the four species showed signs of quick recovery (7–21 days) to normal photosynthetic activity. In a field experiment with simulated run-on, applied to P. clandestinum pasture in sandy loam soil, repeated doses at concentrations up to 1000 μg/L gave no significant response; only a subsequent single dose of 5000 μg/L had significant effects, from which plants soon recovered. Although damage from atrazine can be demonstrated with continuous dosing in non-adsorbing media, in soil culture the tolerance of the four selected species to repeat doses of atrazine shows they may be used confidently for biofiltering purposes. P. clandestinum was especially tolerant.

A dynamic 3D model of root system development was adapted to young sessile oak seedlings, in order to evaluate the effects of grass competition on seedling root system development. The model is based on a root typology and the implementation of a series of developmental processes (axial and radial growth, branching, reiteration, decay and abscission). Parameters describing the different processes are estimated for each root type. Young oak seedlings were grown for 4 years in bare soil or with grass competition and were periodically excavated for root system observation and measurements (topology of the root system, length and diameter of all roots with a diameter greater than 0.3 mm). In the fourth year, 40 cmx20 cmx20 cm soil monoliths were excavated for fine root measurement (root density and root length). Root spatial development was analysed on a sub-sample of roots selected on four seedlings. The model was a guideline that provided a complete and consistent set of parameters to represent root system development. It gave a comprehensive view of the root systems and made it possible to quantify the effects of competition on the different root growth processes. The same root typology was used to describe the seedlings in bare soil and in grass. Five root types were defined, from large tap roots to fine roots. Root system size was considerably reduced by grass competition. Branching density was not affected but the branch roots were always smaller for the seedlings grown in competition. Reiteration capacity was also reduced by competition. Cross sectional areas before and after branching were linearly related with a scaling coefficient close to 1, as predicted by the pipe model theory. This relationship was not affected by grass competition.

A Dehesa is a structurally complex agro-silvo-pastoral system where at least two strata of vegetation, trees and herbaceous plants coexist. We studied the root distribution of trees (Quercus ilex L.) and herbaceous plants, in order to evaluate tree and crops competition and complementarity in Dehesas of Central Western Spain. 72 soil cores of 10 cm diameter (one to two metre deep) were taken out around 13 trees. Seven trees were intercropped with Avena sativa L. and six trees were in a grazed pasture dominated by native grasses. Soil coring was performed at four distances from the tree trunks, from 2.5 (beneath canopy) till 20 m (out of the canopy). Root length density (RLD) of herbaceous plants and trees was measured using the soil core-break method. Additionally, we mapped tree roots in 51 profiles of 7 recently opened road cuts, located between 4 and 26 m of distance from the nearest tree. The depth of the road cuts varied between 2.5 and 5.5 m. Herbaceous plant roots were located mostly in the upper 30 cm, above a clayey, dense soil layer. RLD of herbaceous plants decreased exponentially with depth until 100 cm depth. Holm-oak showed a much lower RLD than herbs (on average, 2.4 versus 23.7 km m−3, respectively, in the first 10 cm of the soil depth). Tree RLD was surprisingly almost uniform with depth and distance to trees. We estimated a 5.2 m maximum depth and a 33 m maximum horizontal extension for tree roots. The huge surface of soil explored by tree roots (even 7 times the projection of the canopy) could allow trees to meet their water needs during the dry Mediterranean summers. The limited vertical overlap of the two root profiles suggests that competition for soil resources between trees and the herbaceous understorey in the Dehesa is probably not as strong as usually assumed.

Exotic invasive plants can alter ecosystem processes. For the first time in Europe, we have analysed the impacts of exotic invasive plants on topsoil chemical properties. At eight sites invaded by five exotic invasive species (Fallopia japonica, Heracleum mantegazzianum, Solidago gigantea, Prunus serotina and Rosa rugosa), soil mineral element composition was compared between invaded patches and adjacent, uninvaded vegetation. We found increased concentrations of exchangeable essential nutrients under the canopy of exotic invasive plants, most strikingly so for K and Mn (32% and 34% increase, respectively). This result fits in well with previous reports of enhanced N dynamics in invaded sites, partly due to higher net primary productivity in exotic invasive plants compared to native vegetation.