Laboratory of Plant Ecology, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Ghent, Belgium.
Grupo de Investigación Sistemas Naturales e Historia Forestal, Universidad Politécnica de Madrid, Madrid 28040, Spain.
Tree Physiol. 2021 Oct 4;41(10):1877-1892. doi: 10.1093/treephys/tpab048.
Elevated atmospheric CO2 concentration (eCO2) commonly stimulates net leaf assimilation, decreases stomatal conductance and has no clear effect on leaf respiration. However, effects of eCO2 on whole-tree functioning and its seasonal dynamics remain far more uncertain. To evaluate temporal and spatial variability in eCO2 effects, 1-year-old European aspen trees were grown in two treatment chambers under ambient (aCO2, 400 p.p.m.) and elevated (eCO2, 700 p.p.m.) CO2 concentrations during an early (spring 2019) and late (autumn 2018) seasonal experiment. Leaf (net carbon assimilation, stomatal conductance and leaf respiration) and whole-tree (stem growth, sap flow and stem CO2 efflux) responses to eCO2 were measured. Under eCO2, carbon assimilation was stimulated during the early (1.63-fold) and late (1.26-fold) seasonal experiments. Stimulation of carbon assimilation changed over time with largest increases observed in spring when stem volumetric growth was highest, followed by late season down-regulation, when stem volumetric growth ceased. The neutral eCO2 effect on stomatal conductance and leaf respiration measured at leaf level paralleled the unresponsive canopy conductance (derived from sap flow measurements) and stem CO2 efflux measured at tree level. Our results highlight that seasonality in carbon demand for tree growth substantially affects the magnitude of the response to eCO2 at both leaf and whole-tree level.
大气二氧化碳浓度升高（eCO2）通常会刺激净叶同化，降低气孔导度，对叶片呼吸没有明显影响。然而，eCO2 对整树功能及其季节动态的影响仍然更加不确定。为了评估 eCO2 影响的时间和空间变异性，我们在两个处理室中种植了 1 年生欧洲白杨，在早期（2019 年春季）和晚期（2018 年秋季）季节实验中，这些树木分别在环境（aCO2，400 ppm）和升高（eCO2，700 ppm）CO2 浓度下生长。我们测量了叶片（净碳同化、气孔导度和叶片呼吸）和整树（茎生长、液流和茎 CO2 排放）对 eCO2 的响应。在 eCO2 下，碳同化在早期（1.63 倍）和晚期（1.26 倍）季节实验中受到刺激。碳同化的刺激随着时间的推移而变化，在春季当茎体积生长最高时观察到最大的增加，随后在秋季当茎体积生长停止时出现后期的下调。在叶片水平测量的 eCO2 对气孔导度和叶片呼吸的中性影响与冠层导度（源自液流测量）和在树木水平测量的茎 CO2 排放的无响应导度相平行。我们的结果强调，树木生长对碳需求的季节性极大地影响了叶片和整树水平对 eCO2 的响应幅度。
