大气CO2浓度升高对小麦蒸腾耗水与根系吸水的影响

为了探索大气CO2浓度升高对作物蒸腾耗水与根系吸水的影响,该文布置了春小麦室内水培试验,试验共设置3个CO2浓度梯度(400±50、625±50、850±50μmol/mol),期间对各处理条件下小麦生长与蒸腾耗水的动态变化过程进行监测,包括水气交换、干物重、叶面积、根长、蒸腾速率等。试验结果表明:当CO2浓度从400μmol/mol升高至625、850μmol/mol时,短期(约3 d)内叶片气孔导度迅速降低,蒸腾耗水减弱,光合作用增强,导致水分利用效率升高;随着小麦被置于高CO2浓度条件下时间的延长,叶片气孔导度与蒸腾速率的降低幅度以及光合速率的增大幅度都逐渐缩小,即发生了CO2驯化现象。此时小麦生长仍然很旺盛,但蒸腾耗水并未发生显著变化,因此水分利用效率升高。CO2浓度升高可显著促进根系生长发育,导致单位根长潜在吸水系数显著降低(P<0.05),但其与单位根长氮含量之间仍呈线性正相关关系(R^2=0.83)。研究结果可为改进根系吸水模型与作物生长模型提供参考依据,并有助于系统理解土壤-作物-大气连续体。

Effects of elevated CO2 concentration on transpiration and root-water-uptake of wheat

Since global atmospheric CO2 concentration is increasing and the gap between water supply and demand is becoming more and more prominent,it is very important to explore the effects of elevated CO2 concentration on water absorption and utilization of crops for meeting climate change.In this study,the effects of elevated CO2 concentration on transpiration and root-water-uptake of wheat were investigated by setting an indoor hydroponic experiment,where wheat seedlings were cultured in half-strength Hoagland nutrient solution and under three CO2 concentrations((400±50),(625±50),(850±50)μmol/mol).During the experimental period,the dynamics of leaf stomata conductance,transpiration rate,photosynthesis rate,leaf area,biomass,root length was monitored every 8 days,and plant transpiration was measured daily by weighing the culture pots.Based on the measured data,plant growth,water uptake and consumption,water use efficiency and the capacity of root water uptake were evaluated under each CO2 concentration condition.The experiment results indicate that,with increasing CO2 concentration(from 400 to 625,850μmol/mol),leaf stomata are partially closed,transpiration rates at both leaf and canopy scales are significantly limited during a short period(about 3 days),and photosynthesis rate is significantly enhanced,resulting in a significant increase in water use efficiency(P<0.05).Compared to the CO2 concentration of 400μmol/mol,the plant transpiration averaged during this short period reduced by 14%and 24%under the CO2 concentration treatment of 625 and 850μmol/mol,respectively.With the prolonging of time under elevated CO2 condition,the effects on leaf stomata conductance,transpiration and photosynthesis are weakened,namely CO2 acclimation,but wheat growth is still significantly promoted.During this period,the positive effect of increased leaf area is almost offset by the reverse effect of stomatal closure,and thus plant transpiration was not impacted significantly,resulting in higher water use efficiency.Compared to the CO2 concentration of 400μmol/mol,plant transpiration averaged during this long period decreased by only 3% and 4%,while plant water use efficiency increased by 59%and 89%under 625 and 850μmol/mol,respectively.Under the situation of elevated CO2 concentration,the limitation of transpiration and the promotion of root growth lead to a significant decrease in root-water-uptake function evaluated on root length(the potential water uptake coefficient per unit root length).Compared to the CO2 concentration of 400μmol/mol,the potential water uptake coefficient per unit root length decreased by average 13% and 31%under 625 and 850μmol/mol,respectively.Under all the CO2 conditions,the change trends of the potential water absorption coefficient per unit root length and the nitrogen content per unit root length are very similar,and a linear function between them is found.The results supply evidences to improve root-water-uptake and crop growth models and further understand soil-plant-atmosphere continuum(SPAC),then,to help us to deal with climate change and improve water use efficiency.