Effects of elevated CO 2 and temperature on leaf characteristics, photosynthesis and carbon storage in aboveground biomass of a boreal bioenergy crop (Phalaris arundinacea L.) under varying water regimes AbstractThis work examined the effects of elevated CO 2 and temperature and water regimes, alone and in interaction, on the leaf characteristics [leaf area (LA), specific leaf weight (SLW), leaf nitrogen content (N L ) based on LA], photosynthesis (light-saturated net carbon fixation rate, P sat ) and carbon storage in aboveground biomass of leaves (C l ) and stem (C s ) for a perennial reed canary grass (Phalaris arundinacea L., Finnish local cultivar). For this purpose, plants were grown under different water regimes (ranging from high to low soil moisture) in climate-controlled growth chambers under the elevated CO 2 and/or temperature (following a factorial design) over a whole growing season (May-September in 2009). The results showed that the elevated temperature increased the leaf growth, photosynthesis and carbon storage of aboveground biomass the most in the early growing periods, compared with ambient temperature. However, the plant growth declined rapidly thereafter with a lower carbon storage at the end of growing season. This was related to the accelerated phenology regulation and consequent earlier growth senescence. Consequently, the elevation of CO 2 increased the P sat , LA and SLW during the growing season, with a significant concurrent increase in the carbon storage in aboveground biomass. Low soil moisture decreased the P sat , leaf stomatal conductance, LA and carbon storage in above ground biomass compared with high and normal soil moisture. This water stress effect was the largest under the elevated temperature. The elevated CO 2 partially mitigated the adverse effects of high temperature and low soil moisture. However, the combination of elevated temperature and CO 2 did not significantly increase the carbon storage in aboveground biomass of the plants.
The aim of this work was to study the acclimation of photosynthesis in a boreal grass (Phalaris arundinacea L.) grown in controlled environment chambers under elevated temperature (ambient + 3.5 o C) and CO 2 (700 μmol mol −1 ) with varying soil water regimes. More specifically, we studied, during two development stages (early: heading; late: florescence completed), how the temperature response of light-saturated net photosynthetic rate (P sat ), maximum rate of ribulose-1,5-bisphosphate carboxylase/oxygenase activity (V cmax ) and potential rate of electron transport (J max ) acclimatized to the changed environment. During the early growing period, we found a greater temperature-induced enhancement of P sat at higher measurement temperatures, which disappeared during the late stage. Under elevated growth temperature, V cmax and J max at lower measurement temperatures (5-15°C) were lower than those under ambient growth temperature during the early period. When the measurements were done at 20-30°C, the situation was the opposite. During the late growing period, V cmax and J max under elevated growth temperature were consistently lower across measurement temperatures. CO 2 enrichment significantly increased P sat with higher intercellular CO 2 compared to ambient CO 2 treatment, however, elevated CO 2 slightly decreased V cmax and J max across measurement temperatures, probably due to down-regulation acclimation. For two growing periods, soil water availability affected the variation in photosynthesis and biochemical parameters much more than climatic treatment did. Over two growing periods, V cmax and J max were on average 36.4 and 30.6%, respectively, lower with low water availability compared to high water availability across measurement temperatures. During the late growing period, elevated growth temperature further reduced the photosynthesis under low water availability. V cmax and J max declined along with the decrease in nitrogen content of leaves as growing period progressed, regardless of climatic treatment and water regime. We suggest that, for grass species, seasonal acclimation of the photosynthetic parameters under varying environmental conditions needed to be identified to fairly estimate the whole-life photosynthesis.
The effects of elevated growth temperature (ambient + 3.5 o C) and CO 2 (700 µmol mol −1 ) on leaf photosynthesis, pigments and chlorophyll fluorescence of a boreal perennial grass (Phalaris arundinacea L.) under different water regimes (well watered to water shortage) were investigated. Layer-specific measurements were conducted on the top (younger leaf) and low (older leaf) canopy positions of the plants after anthesis. During the early development stages, elevated temperature enhanced the maximum rate of photosynthesis (P max ) of the top layer leaves and the aboveground biomass, which resulted in earlier senescence and lower photosynthesis and biomass at the later periods. At the stage of plant maturity, the content of chlorophyll (Chl), leaf nitrogen (N L ), and light response of effective photochemical efficiency (Φ PSII ) and electron transport rate (ETR) was significantly lower under elevated temperature than ambient temperature in leaves at both layers. CO 2 enrichment enhanced the photosynthesis but led to a decline of N L and Chl content, as well as lower fluorescence parameters of Φ PSII and ETR in leaves at both layers. In addition, the downregulation by CO 2 elevation was significant at the low canopy position. Regardless of climate treatment, the water shortage had a strongly negative effect on the photosynthesis, biomass growth, and fluorescence parameters, particularly in the leaves from the low canopy position. Elevated temperature exacerbated the impact of water shortage, while CO 2 enrichment slightly alleviated the drought-induced adverse effects on P max . We suggest that the light response of Φ PSII and ETR, being more sensitive to leaf-age classes, reflect the photosynthetic responses to climatic treatments and drought stress better than the fluorescence parameters under dark adaptation. Abbreviations: Cars -carotenoid; Chl -chlorophyll; Chl a(b) -chlorophyll a(b); CON -ambient environment; EC -elevated CO 2 concentration; ET -elevated temperature; ETC -combination of temperature elevation and CO 2 enrichment; ETR -electron transport rate; F m -maximal chlorophyll fluorescence of dark-adapted state; F m ' -maximal chlorophyll fluorescence of light-adapted state; F 0 -minimum chlorophyll fluorescence of dark-adapted state; F 0 ' -minimum chlorophyll fluorescence of light-adapted state; F s -steady state fluorescence; F v /F m -maximal photochemical efficiency of PSII; g sat -light-saturated stomatal conductance; HW -high water level; LW -low water level; N L -leaf nitrogen; NW -normal water level; NPQ -nonphotochemical quenching; P max -maximum rate of photosynthesis; P N -net photosynthetic rate; PPFD -photosynthetic photon flux densities; PSII -photosystem II; q P -photochemical quenching; R D -dark respiration rates; RCG -Reed canary grass; Rubisco -ribulose 1,5-bisphosphate carboxylase/ oxygenase; RuBP -ribulose bisphosphate; α -apparent quantum yield; Φ PSII -the effective photochemical efficiency. Acknowledgments: This work was funded through the Finland Distinguished Professor Progra...
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