枫杨幼苗对土壤水分"湿-干"交替变化光合及叶绿素荧光的响应

以盆栽1年生枫杨幼苗为实验材料,通过人工设置土壤水分来模拟三峡库区消落带不同土壤水分对枫杨幼苗的光合参数、光合色素含量、叶绿素荧光特性等的影响.试验设置4个处理组,分别为常规供水、常规供水-轻度干旱-复水、水淹、水淹-轻度干旱-复水,3个处理期分别为前期(0-33 d)、中期(34-63 d)、后期(64-78 d).结果表明,不同的水分处理显著地影响了枫杨幼苗“表观性”的气体交换、光合色素含量和水分利用效率等特性,但相较而言对枫杨幼苗“内在性”的叶绿素荧光特性影响较小,且影响的结果和程度因处理组和指标而异.78 d时,除胞间CO2浓度(Gi)、叶绿素a/叶绿素b、光化学猝灭值(qP)和非光化学淬灭值(qN)外,水淹组(FL组)的各项指标在4个处理组中都为最低值;“湿-干”交替组(FD组)的净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)及总叶绿素含量则表现出先降低复水后显著增加的趋势;DR组的变化趋势与FD组类似,但变化的幅度较FD组小.研究发现,枫杨幼苗面对不同水分状况呈现出了一定的敏感特性,但随着胁迫时间的延长其无论是从光合、水分利用还是叶绿素荧光特性方面都表现出积极的响应,较能适应干旱、水淹、“湿-干”交替等多种环境胁迫,且在胁迫解除后能够迅速恢复生长,可以考虑用于三峡库区消落带的植被重建.

Response of photosynthesis and chlorophyll fluorescence characteristics of Pterocarya stenoptera seedlings to submergence and drought alternation

The Three Gorges Dam has created a new riparian zone which is called 30m-water-level fluctuating zone of the Three Gorges Reservoir of the Yangtze River. Altered ecosystems of the riparian zone can disrupt the hydrological regime by reducing inundation, or creating longer term submergence, which adversely affects riparian vegetation, and in particular, the native plant species. Chinese wingnut (Pterocarya stenoptera) is a dominant native riparian tree species in the Three Gorges Reservoir region, and thus has to face the modified riparian environment. In order to shed light on the impacts of soil water regimes in this region on the Chinese wingnut, 4 water treatments were imposed on 1-year-old seedlings of Chinese wingnut for more than 2 months. The water treatments included normal water supply (CK), normal water supply-light drought-normal water supply (DR), flooding (FL) and flooding-light drought-normal water supply (FD), which simulated the modified hydrological regime in the riparian zone of the Three Gorges Reservoir region. The treatment of 3 stages for DR and FD groups lasted 33, 30 and 15 days respectively. The effects of water treatments on photosynthetic parameters, photosynthetic pigment contents and chlorophyll fluorescence characteristics of Chinese wingnut seedlings were investigated after 0, 33, 63 and 78 days of water treatment. The results showed that net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), photosynthetic pigment contents (chlorophyll a, chlorophyll b and carotenoid) and water use efficiency (WUE) of Chinese wingnut seedlings were reduced significantly in DR, FL and FD treatments as compared to CK. However, the chlorophyll fluorescence features of Chinese Wingnut seedlings in these three treatments were slightly reduced comparable to that of CK. Compared to other three treatments, seedlings in FL group were adversely influenced dramatically. At the end of the treatment, the Pn of Chinese wingnut seedlings under FL treatment was reduced by 65.9%,WUE was reduced by 65.7%, and total chlorophyll content was reduced by 68.7% comparing with that of CK. In contrast to CK group, Pn, Tr, Gs and total chlorophyll in FD groups were also decreased significantly in the beginning of the treatment due to flooding and drought, but they were increased significantly after rehydration. The seedlings in DR groups showed similar but lower variation as to those of FD. The results suggested that the seedlings of Chinese wingnut were sensitive to soil water stress including flooding and drought, although they showed obvious tolerant ability to water stress in terms of the characteristics of morphology, photosynthesis, water use efficiency and chlorophyll fluorescence. Additionally, all of them showed excellent recovery ability after stress being released. Therefore, Chinese wingnut might be suitable to the modified hydrological regime caused by the Three Gorges Dam, and thus could be applied to vegetation reconstruction in the water-level fluctuating zone of the Three Gorges Reservoir for its adaption to drought, flooding and "flooding-drought" alternative variation.