土壤水分对沙棘光合日变化的影响

摘要

探索土壤水分对沙棘光合日变化的影响对于深入了解黄土高原地区沙棘的光合生理和水分生态特性具有重要意义.文章应用CIRAS-2型光合作用系统,测定了3 年生沙棘叶片光合作用气体交换参数在不同( 8个)土壤水分含量下的日变化过程,研究了土壤水分变化对沙棘光合作用效能的影响.结果表明:土壤含水量明显影响沙棘光合日变化过程,当土壤相对含水量( RWC)在50. 4% ~62. 4%时,沙棘的净光合速率( Pn )全天处于较高水平,且无"午休"现象;RWC超出此范围时,全天的Pn 均下降,并伴随光合"午休"现象;沙棘光合"午休"的主要原因与土壤含水量有关,当RWC减少至36. 3%时,沙棘光合"午休"现象加重且其导致光合"午休"主要原因由气孔限制转变为非气孔限制.%In the study,photosynthetic parameters in leaves of three-year-old Hippophae rhamnoides L. grown in pots were tested under 8 soil water contents to investigate daily variation course of drought stress on photosynthesis and the relationship between photosynthesis and soil water content by using CIRAS-2 portable photosynthesis system in the semiarid loess hilly region. The results show that:Changes in soil moisture content significantly affect the diurnal variation of photosynthesis in leaves of Hippophae rhamnoides L. . When relative soil water content(RWC)is within the scope of 50. 4% ~62. 4%,the net photosynthetic rate( Pn ) keeps at high levels throughout the day and midday depression of photosynthesis does not occur;while RWC is outside this range ( increasing or decreasing),the day level of Pn decreases and midday depression occurs,low ebbs appeares at 11:00 ~ 13:00. The main reason for midday depression in Hippophae rhamnoides L. is related to the variation of RWC. When RWC reduced to 36. 3%,midday depression of photosynthesis aggravated and the main reason for midday depression changed from stomatal limitation to non-stomatal limitation.