Populus euphratica and Poulus pruinosa are keystone species of desert ecosystems, their existence and development affect the structure, function and sustainable development of the Tarim desert ecosystem. They are precious in Tarim basin for their great ecological, economical and social benefits. In this work, We studied the effect of groundwater depths and different weathers on the photochemical efficiency of PSII, excitation energy dissipation and photosystem health of the P. euphratica and P. pruinosa with a portable fluorometer (PAM-2100). The results showed that the actual photochemical efficiency of PSII in the light(ΦPSI ), photochemistry quenching (qP), potential photosynthetic activity(Fv/Fo), the maximal photochemical efficiency of PSII (Fv/Fm), maximal fluorescence(Fm), electron transportation activity(Fm/Fo)and the ratio of absorbed light in the photochemistry(P)of these two tree species decreased from sunny days to cloudy days and with increasing groundwater depth, whereas the non-photochemistry quenching (NPQ), the ratio of the antenna thermal dissipation (D) and the excess excited energy(E) increased remarkably in the same conditions. But Fv/Fm of both tree species could well maintain optimum values (close to 0.80) under different habitats. The chlorophyll fluorescence parameters of both species were affected significantly by high light and groundwater depth interaction. The interactions between strong sunlight and groundwater depth enhanced the chance of the PSII damage, significantly inhibitedΦPSI and decreased the percentage of the PSII photochemical reaction energy, which resulted in lower photosynthesis. But these two species had good stress-resistances and self-regulation mechanisms, which can improve NPQ and E to alleviate injuries on the photosynthetic apparatus and always keep higher activities of photosynthetic electron transportation, this contributed to their high photosynthetic capacity. The percentages of the absorbed light allocation of both species were affected significantly by the high light and groundwater depth interactions. The P. euphratica could maintain higher P and increase D to decrease the level of injuries under different habitats. It indicated the P. euphratica had stronger ecological adaptation than the P. pruinosa. The P of these two tree species decreased while D and E increased with groundwater depth descending. But the P.pruinosa had higher E and lower P, D than the P. euphratica, which indicated the P. euphratica could reasonably allocate the absorbed light energy and maintain a higherΦPSI and photosynthetic activity in drought conditions. In summary, the P. euphratica has a higher self-adjustment ability and ΦPSI , it could maintain an optimum strategy of the absorbed light allocation under various stresses than the P.pruinosa and this is the primary reason why it has a wider distribution and survival than the latter species in the extreme arid desert area in the Tarim Basin.% 胡杨与灰胡杨是干旱荒漠生态系统的关键种,其存在与发展决定着塔里木荒漠生态系统的结构、功能与可持续发展.利用PAM-2100(WALZ, Germany)研究并分析了天气类型与地下水位对胡杨、灰胡杨PSII光化学效率和激发能耗散及光系统健康状况的影响.结果表明：胡杨与灰胡杨的Fm、Fv/Fo、Fm/Fo、Fv/Fm、qP、ΦPSI 及P值均随天气由阴天至晴天而降低,并随地下水位下降而降低,而NPQ、D与E值则随阴天至晴天及地下水位下降而显著升高.不同生境2树种最大光化学量子产量(Fv/Fm)总体处于相对适宜状态(0.80左右).天气类型×地下水位互作极显著影响2树种叶绿素荧光参数.晴天强光与地下水位互作增强了2树种光合机构光损伤机会,显著抑制了PSII光化学活性,降低了PSII光能捕获效率与光化学反应份额而导致光合活性与光合能力降低.但2树种可通过迅速增强非辐射热耗散来缓解水分胁迫与强光、高温对光合机构的伤害,以此保护光合机构正常运转,这是其光合性能较高的生理原因之一.天气类型×地下水位互作显著影响2树种光能吸收分配策略.不同天气类型下胡杨均能保持较高的 P,且合理分配吸收光能以增加 D 来抵御强光对其的伤害,反映了胡杨对强光辐射适应能力强于灰胡杨.随地下水位下降2树种P值降低,D、E值升高.相同地下水位灰胡杨E值略高胡杨,而D、P值则低于胡杨,表明胡杨在干旱胁迫下仍能合理分配吸收光能,保持较高的PSII光化学效率和光合活性.胡杨对多种胁迫因子共存的极端荒漠环境具有较强的自我调节能力,其适应荒漠生境的生理生态策略优于灰胡杨,这是其在极端干旱荒漠区长期生存与广泛分布的原因之一.
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