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Temperate plants may show different photosynthetic acclimation capacities, involving varying physiological processes/mechanisms, during different seasons in response to global warming because of seasonal climate variation. Thus, we conducted field warming experiments for winter wheat in its four seasonal periods. These experiments allowed us to examine the thermal acclimation of photosynthesis and the underlying processes/mechanisms (RuBP-carboxylation, RuBP-regeneration, stomatal conductance and the balance between respiration and photosynthesis) to both seasonality and warming effects as well as the interaction between them. We found winter wheat displayed nonlinear acclimation to the seasonal temperature change, and significant acclimation to experimental warming in the four seasons. However, the acclimation capability in response to experimental warming was lower in January than November/April/May. Importantly, the underlying physiological processes/mechanisms to warming effects vary among seasonal periods: RuBP carboxylation contributed to the acclimation of photosynthesis in November and April, while the balance between respiration and photosynthesis caused the major change in January, and lower stomatal conductance played the most important role in May. These results could give insights into the decrease in productivity and increase of biomass accumulation and could help to predict acclimation capability and underlying processes to global warming. In addition, photosynthetic parameters reported here could be used to incorporate seasonal dynamics of thermal acclimation into physiological-process-based ecosystem models. [ABSTRACT FROM AUTHOR]

Spartina alterniflora is the dominant grass appearing in salt marshes along the east coast of the USA. The development of predictive, mechanistic models of Spartina has been hindered by the lack of information on below-ground biomass and its dynamics, and in particular the storage of resources that can be used for spring re-growth. We studied the dynamics of non-structural carbohydrates (glucose, fructose, sucrose, and starch) and biomass in 8 different above- and below-ground tissues in S. alterniflora over the course of a year in a salt marsh on Sapelo Island, Georgia, USA. We found greater seasonal variability in non-structural carbohydrates in S. alterniflora than had been previously reported, with concentrations varying between 3.3% through 17.3% of the total biomass and between 0% and 19.5% of dry weight depending on the type of tissue, with statistical differences between the different tissues. We found that sucrose was the dominant non-structural carbohydrate in above- and below-ground tissue, and that this sugar was likely used for long-term storage during winter months and as a resource for early spring growth. Glucose, fructose, and starch showed less variability, with glucose following changes in above-ground biomass more closely indicating their use as short-term storage. We were unable to develop a coherent carbon budget for the plants largely because of uncertainties in modeled net primary production and heterogeneity in below-ground biomass. [ABSTRACT FROM AUTHOR]

Since a substantial portion of respired CO2 remains within the stem, diel and seasonal trends in stem CO2 concentration ([CO2]) are of major interest in plant respiration and carbon budget research. However, continuous long-term stem [CO2] studies are scarce, and generally absent in Mediterranean climates. In this study, stem [CO2] was monitored every 15 min together with stem and air temperature, sap flow, and soil water storage during a growing season in 16 stems of Quercus pyrenaica to elucidate the main drivers of stem [CO2] at different temporal scales. Fluctuations in sap pH were also assessed during two growing seasons to evaluate potential errors in estimates of the concentration of CO2 dissolved in xylem sap ([CO2*]) calculated using Henry's law. Stem temperature was the best predictor of stem [CO2] and explained more than 90% and 50% of the variability in stem [CO2] at diel and seasonal scales, respectively. Under dry conditions, soil water storage was the main driver of stem [CO2]. Likewise, the first rains after summer drought caused intense stem [CO2] pulses, suggesting enhanced stem and root respiration and increased resistance to radial CO2 diffusion. Sap flow played a secondary role in controlling stem [CO2] variations. We observed night-time sap pH acidification and progressive seasonal alkalinization. Thus, if the annual mean value of sap pH (measured at midday) was assumed to be constant, night-time sap [CO2*] was substantially overestimated (40%), and spring and autumn sap [CO2*] were misestimated by 25%. This work highlights that diel and seasonal variations in temperature, tree water availability, and sap pH substantially affect xylem [CO2] and sap [CO2*]. [ABSTRACT FROM AUTHOR]

Rice-wheat (R-W) rotation systems are ubiquitous in South and East Asia, and play an important role in modulating the carbon cycle and climate. Long-term, continuous flux measurements help in better understanding the seasonal and interannual variation of the carbon budget over R-W rotation systems. In this study, measurements of CO fluxes and meteorological variables over an R-W rotation system on the North China Plain from 2007 to 2010 were analyzed. To analyze the abiotic factors regulating Net Ecosystem Exchange (NEE), NEE was partitioned into gross primary production (GPP) and ecosystem respiration. Nighttime NEE or ecosystem respiration was controlled primarily by soil temperature, while daytime NEE was mainly determined by photosythetically active radiation (PAR). The responses of nighttime NEE to soil temperature and daytime NEE to light were closely associated with crop development and photosynthetic activity, respectively. Moreover, the interannual variation in GPP and NEE mainly depended on precipitation and PAR. Overall, NEE was negative on the annual scale and the rotation system behaved as a carbon sink of 982 g C m per year over the three years. The winter wheat field took up more CO than the rice paddy during the longer growing season, while the daily NEE for wheat and rice were -2.35 and -3.96 g C m, respectively. After the grain harvest was subtracted from the NEE, the winter wheat field became a moderately strong carbon sink of 251-334 g C m per season, whereas the rice paddy switched to a weak carbon sink of 107-132 per season. [ABSTRACT FROM AUTHOR]

Aimed: The main aim of this study is to improve the mechanistic understanding of soil CO efflux (F), especially its temporal variation at short-time scales, by investigating, through modeling, which underlying process among CO production and its transport up to the atmosphere is responsible for observed intra-day variation of F and soil CO concentration [CO]. Methods: In this study, a measurement campaign of F and vertical soil [CO] profiles was conducted in a Scots Pine Forest soil in Hartheim (Germany) and used to develop a model testing several hypotheses. A reference model taking into account a purely diffusive CO transport and a temperature-dependent CO production is compared to models with a more complex description of either CO production or CO transport. For transport, the introduction of advection and the dispersion is investigated. For the production, the emergent hypothesis of the phloem pressure concentration wave (PPCW) influence is tested. Results: We show that intra-day variation of F and [CO] is better represented when the more complex CO production expression is taken into account compared to the more detailed description of CO transport. Conclusion: We conclude that focus should be placed on the potential factors affecting the CO production, rather than on the transport process description [ABSTRACT FROM AUTHOR]

In the present study, the physiological efficiencies of 181 mini-core peanut accessions (genotypes) were evaluated according to variability in their physiological performance in the field during summer (2012). Genotypes were categorized into groups of high, medium, and low physiological activity. Thirty-four genotypes showed high net photosynthetic rate ( P > 33 μmol m s), 28 genotypes exhibited high stomatal conductance ( g > 0.54 mmol m s), 33 genotypes manifested high transpiration rate ( E > 11.8 mmol m s), 30 genotypes performed with high water-use efficiency (WUE > 3.8), 30 genotypes reached high chlorophyll SPAD values (SCMR > 40), and 35 genotypes showed high maximum quantum yield of PSII (F/F > 0.86). In addition, few genotypes showed high values for multiple physiological traits. A total of 54 genotypes exhibited higher values in two, 20 genotypes showed a high value in three, and in eight genotypes, high values occurred in four different physiological traits. Interestingly, only two genotypes, NRCG 14493 and 14507, showed high values for five different traits. Positive correlation was observed between g and P, E, and g, and between P and F/F, while WUE and E showed a negative correlation. The genotypes with high P, g, and WUE coupled with high SCMR and F/F could be used in peanut crop improvement programme for yield enhancement as well as stress tolerance. [ABSTRACT FROM AUTHOR]