荒漠草原石生针茅光合特性对渐进式土壤干旱过程的响应及敏感性分析

Response and sensitivity of photosynthesis of Stipa tianschanica in desert steppe to developing soil drought process

陆地生态系统碳收支对极端气候变化十分敏感。为探究石生针茅荒漠草原碳收支对土壤极端干旱过程的响应机制,本研究以荒漠草原石生针茅为试验材料,采用遮雨棚人工控水方法模拟土壤的极端干旱过程,测定多项石生针茅碳交换特征参数,分析其变化特征并对比不同参数对干旱的敏感性差异。结果表明:水分利用效率(WUE)与土壤含水量(SWC)呈显著的指数关系,气孔导度(G_(s))、最大羧化速率(V_(cmax))和磷酸丙糖利用率(TPU)与SWC呈显著的线性关系,其余特征参数与SWC均呈显著的二次曲线关系,且在干旱胁迫下叶片尺度的特征参数最先出现下降响应;饱和光强下叶片净光合速率(A_(sat))、蒸腾速率(E)、最大电子传递速率(J_(max))、PSⅡ的有效光化学量子产量(Fv′/Fm′)、PSⅡ的实际光化学效率(ΦPSⅡ)和生态系统净碳交换(NEE)均存在水分阈值;在干旱过程中,Gs、WUE、Vcmax、TPU、生态系统呼吸速率(Re)和生态系统总初级生产力(GEP)最先开始下降,E、NEE和Jmax的整体变化速率较快;导致石生针茅叶片光合速率下降的主要原因由气孔限制转为非气孔限制时的SWC为14.73%,而石生针茅生态系统由碳汇转变为碳源的SWC为7.85%。可见,石生针茅生态系统的碳交换与土壤含水量密切相关,且土壤极端干旱显著降低了其碳吸收。

Terrestrial ecosystem carbon budgets are sensitive to extreme climate events.To understand the carbon budget response in Stipa tianschanica desert steppe to extreme drought process,a manipulative experiment involving extreme soil extreme drought process was conducted under a rainout shelter.A range of characteristic parameters of S.tianschanica were measured and analyzed,and sensitivity to drought of the various parameters was also evaluated.It was found that water use efficiency(WUE)showed a significant exponential relationship with soil water content(SWC).Stomatal conductance(G_(s)),maximum carboxylation rate(V_(cmax))and triose phosphate utilization rate(TPU)showed significant liner relationships with SWC.There were also significant quadratic relationships between other carbon exchange parameters and SWC.CO2 exchange activities of S.tianschanica at leaf scale were more sensitive to soil drought.Light-saturated net photosynthetic rate(A_(sat)),transpiration rate(E),maximum electron transfer rate(J_(max)),photochemical efficiency of PSⅡin the light(Fv'/Fm'),actual photochemical efficiency of PSⅡin the light(ΦPSII)and net ecosystem CO2 exchange(NEE)showed clear thresholds of soil moisture.Gs,WUE,Vcmax,TPU,ecosystem respiration(Re)and gross ecosystem production(GEP)began to decrease when SWC started to decline,while E,NEE and Jmax exhibited rapid rates of change under drought condition.14.73%and 7.85%were two critical SWC at which the inhibition of leaf photosynthesis changed from stomatal limitation to non-stomatal limitation and the ecosystem shifted from sink to source,respectively.In conclusion,carbon exchange of S.tianschanica ecosystem was significantly related to SWC and carbon sink was significantly inhibited under extreme soil moisture deficit.