黄河三角洲柽柳对水位-盐分变化的生理生态响应过程与机制

Groundwater resource is abundent in the silting coastal area of Laizhou Bay in Yellow River Delta, but the water that can be used effectively by natural vegetations is very limited due to restricting of groundwater depth and quality; especially the shallow groundwater table and high mineralization are the main causes of salinization in this region. Based on the ecological problems of the influences in the depth and mineralization of groundwater on growth of tree and forests degradation in the silting coastal arear, our objective is to investigate the process of salt and water movements in groundwater-soil-plant continuum, and its effect on ecophysiological characteristics of T. chinensis. Taking the constructive species of T. chinensis under different groundwater depth and mineralization level in Yellow River Delta as test objects, using the theory and methods of stable hydrogen and oxygen isotope, sap flow, chlorophyll fluorescence and gas exchange etc., the characteristics of salt and water movements in the vector of source-sink-translocation, and their effects on the physiological ecology of photosynthesis and water will be studied. The research will focus on: ① the characteristics of salt and water migration in groundwater-different soil layer- main organ of T. chinensis continuum and their influencing factors, ② the response rule and regulatory mechanism of photosynthetic physiological ecology of T. chinensis under different groundwater depths and mineralization level, ③ water transport process and its energy state driving mechaninisms with synergism of salt and water, ④ different potential water sources of T. chinensis and the adaptive strategy of salt-water under different groundwater depths and mineralization level. The results could provide important scientific value and realistic significance for a deeper appreciation of plant ecophysiological characteristics and its relation with the salt-water in the vector of groundwater-soil, and enrich research on the mechanism of vegetation restoration and reconstruction of degraded soil and water conservation forests on saline-alkali soil in silting coastal area.

针对泥质海岸带树木生长及林分退化受地下水水位及其矿化度影响较大这一突出问题,以揭示地下水-土壤-植物体的水盐迁移过程与柽柳生理生态特征及其两者的关系为目标，选取黄河三角州莱州湾不同水位-盐分生境下的建群种-柽柳为研究对象，基于氢氧稳定同位素和植物液流信息技术，结合叶片气体交换和叶绿素荧光监测技术与理论分析方法，开展源库流关系构建下的水盐迁移特征及其协同影响柽柳光合及水分生理生态过程的研究。探索在地下水-不同土壤层-柽柳主要器官等不同介质层面的水盐迁移特征及其影响因素，揭示柽柳光合生理生态过程对水位-盐分的响应规律及其生理调节机理，阐明水盐协同作用下柽柳的水分传输规律及其能态驱动机制，明确盐分生境下柽柳的水分利用来源及其水盐适应策略。研究成果可为植物生理过程与水盐关系的深入研究提供在地下水-土壤主要介质层面的理论基础，对泥质海岸退化水土保持防护林的植被恢复与重建具有重要的理论价值和参考作用。

地下水是影响黄河三角洲柽柳生长及分布的主要影响因子。本研究探讨了不同地下水水位及其矿化度下的土壤-柽柳系统的水盐迁移特征及其交互效应，揭示了柽柳对水位-盐分变化的生理生态响应过程与机制。研究发现：[1] 地下水水位及其矿化度可显著影响柽柳-土壤系统的水盐分布。随潜水埋深的增加，柽柳土柱、柽柳叶片和新生枝条含水量逐渐下降，柽柳叶片含盐量先降低后升高，而柽柳土柱和新生枝条含盐量先升高后降低；柽柳由枝条向叶片转移的水分显著增加，而Na+迁移比例先降低后升高。1.2 m水位是土壤水盐变化的转折点，此水位下各土壤剖面的含盐量和土壤溶液绝对浓度均达最高。随地下水矿化度的升高，土柱的含水量和含盐量均升高，而土壤溶液绝对浓度降低。栽植柽柳可显著降低土柱的含水量、含盐量和土壤溶液绝对浓度，但随地下水矿化度的升高，栽植柽柳对土壤水分的降低作用在减弱，而抑制盐分作用在增强。[2] 柽柳光合及水分生理参数与地下水水位及其矿化度密切相关。在1.2 m的潜水埋深下，地下水矿化度通过影响土壤盐分可显著影响柽柳光合特性及耗水性能。随地下水矿化度升高，柽柳叶片净光合速率、表观量子效率和暗呼吸速率均先升高后降低，而水分利用效率持续降低。柽柳树干液流量随地下水矿化度升高先增加后减少。咸水矿化度下柽柳有较高的光合特性，在蒸腾耗水较严重的情况下可实现高效生理用水。盐水矿化度下，随潜水埋深的增加，柽柳叶片净光合速率和实际光化学效率先升高后降低。潜水埋深0.9 m时柽柳叶片净光合速率和PSII实际光化学效率最高。水盐逆境下柽柳可通过多种光破坏防御机制，耗散部分过剩光能，降低光破坏的危害。[3] 明确了不同潜水水位下柽柳的水分利用机制。在湿季，低水位柽柳的水分91%来源于20-40cm土壤水，高水位柽柳的水分51%来源于60-100cm土壤水；在干季，低水位柽柳的水分57%来源于20-60cm土壤水，而高水位柽柳的水分67%来源于浅层地下水。研究结果可为地下水作用下土壤次生盐渍化的防治和柽柳栽植管理提供参考。