黑河下游荒漠植被生态过程及水文驱动研究

Desert vegetation is an indicator of environmental change, especially hydrological changes in the inland river basin. Ecological process interacts with hydrological process, and hydrological process drives ecological process showing pattern change. Based on the experiments and investigations in the observation sites of typical desert, Gobi desert and sandy desert ecosystem which are laid previously in lower reaches of Heihe River. According to different desert ecosystem types, auxiliary observation fields are added on the basis of the distance to Heihe and life form of dominant species, and connect with integrated study of coupling model of eco-hydrological process in the middle and lower reaches, research emphasis is strengthened and necessary research contents are supplemented. Many researches are carried out including observation and study of water consumption and water consumption law of desert plants under different water conditions, investigation and determination of physic-ecological characteristics of dominant species of desert vegetation under different hydrological conditions, study of structural and functional features of different desert plant communities along with changes of surface water, precipitation and groundwater. The study of the above questions help to know the hydrological driving mechanism of water requirement and water consumption of life-form functional groups of desert plants in the lower reaches of Heihe River, to reveal evolution process and patterns of desert ecosystem under different water environment in the lower reaches of Heihe River. It provides information for building a distributed ecological-hydrological coupling model and desert ecosystem module; and theoretic guide for conservation of desert ecosystem and management of oasis ecosystem in the Heihe River basin.

荒漠植被是内陆河流域环境变化，特别是水文变化的指示器。生态过程与水文过程相互作用，水文过程驱动生态过程呈现格局变化。在前期布设的下游荒漠、戈壁、沙漠生态系统调查观测场和实验观测场，开展调查观测和试验研究基础上，根据不同荒漠生态系统类型，按距离黑河远近和优势植物生活型，增设辅助调查观测场，与中下游生态水文过程耦合模型集成研究衔接，强化研究重点，增补必须研究内容。开展荒漠植被在不同水分条件下的耗水量和耗水规律观测研究，调查测定不同水文条件下荒漠植被优势种的生理生态学特性，研究不同类型荒漠植物群落结构和功能随地表水、降水和地下水变化的特征。认识黑河下游荒漠植物生活型功能群需水量及耗水规律的水文驱动机制，揭示黑河下游不同水环境下的荒漠生态系统演变过程和格局。为黑河中下游地区分布式生态—水文耦合模型，荒漠生态系统模块的构建提供资料；为内陆河流域荒漠生态系统保育和绿洲生态系统管理提供理论指导。

在黑河下游以前布设的沙漠(沙质荒漠sand desert)、戈壁(砾质荒漠gravel desert)和荒漠(壤质荒漠silt desert)三个不同类型调查观测场基础上，沿黑河主河道垂直方向由近到远不同水盐梯度下，布设了辅助调查样地。开展了植物种类组成和盖度、密度、冠幅、高度等数量特征和土壤调查；全根法调查了优势种红砂(Reaumuria soongorica)、沙拐枣(Calligonum mongolicum)、黑果枸杞(Lycium ruthenicum)、泡泡刺(Nitraria sphaerocarpa)、花花柴(Karelinia caspica)、骆驼蓬(Peganum harmala)、苦豆子(Sophora alopecuroides)和柽柳(Tamarix ramosissima)等的根系分布幅度、深度和地下生物量；采集了植物叶片、茎干、根系及样地土壤样品并进行了分析；进行了Lysimeter和红外气体分析仪测定植物蒸腾和土壤蒸发的对比观测；比较了不同生活型荒漠植物和同一荒漠植物在不同水文条件下的叶片和群体光合作用和蒸腾作用。按计划完成任务并提交了数据。.根冠比分析得出，非地带性植物柽柳最高，达到9.4，荒漠植物红砂、沙拐枣、泡泡刺和苦豆子的根冠比大于1；黑果枸杞、花花柴和骆驼蓬的地上生物量大于地下生物量，根冠比小于1。说明红砂、沙拐枣、泡泡刺、苦豆子和柽柳生物量主要分配到地下，相比黑果枸杞、花花柴和骆驼蓬，维持生存需要占据更大的地下土壤空间。全根法调查荒漠植物地下生物量，发现红砂和沙拐枣在戈壁依赖年天然降水＜40 mm生存时根系分布深度小于1 m。生长在壤质荒漠依赖天然降水生存的黑果枸杞也有类似的特征，根系分布深度不超过1 m，达到80 cm左右后水平迂回生长；但黑果枸杞在沙漠丘间低地根系分布深度增加，在1 m以下，反映了荒漠植物根系的趋水性。通过红外气体分析仪测定水汽通量和小型Lysimeter称重计算植物蒸散量的比较得出，相对误差平均为5.8%，水汽通量测定结果相对更可靠。黑河下游广泛分布的黑果枸杞嫩枝和枯枝相伴生长，地上枯枝的这种生态作用，可减少10%以上的土壤蒸发量。不同生活型荒漠植物蒸腾速率观测表明，多年生草本植物苦豆子的耗水量小于灌木黑果枸杞，与Lysimeter观测结果一致。荒漠植物在雨后湿润条件下具有更高的水分利用效率。