极干旱区洪水驱动的植物分布格局与生存策略

As the only life corridor for plant dispersal and animal migration, flood ditch is an important part for maintaining the stability of the ecosystem in the hyperarid region. But flood process， plant patterns and plant water use strategy for survival are unclear in the flood ditch. Previous studies showed that plants could use pulse water in surface soil or stable water source in deep soil through plasticity of root and leaf stoma. The vegetation is mainly distributed at upper, lower location of the flood ditch. High precipitation, small runoff and fast water cycle are the hydrological characteristics at upper location of the flood ditch. Low precipitation and flood frequency and slow water cycle are the hydrological characteristics at lower location of the flood ditch. In addition, the groundwater is very deep in the valley of the flood ditch. Few studies reported plant water use strategy for stable survival in this environment. In this study, we will examine the flood and soil moisture dynamic characteristics by collecting flood frequency, distribution, water infiltration and soil moisture in Cuimutu ditch, and plant water use strategy by collecting dynamic data of soil moisture and plant transpiration at upper, lower location of the flood ditch. This study will be helpful to perfect the eco-hydrology research content of China, ensure strategy layout of Silk Road Economic Belt, and promote regional ecological security.

洪沟作为极干旱区绿洲外围唯一的植物扩散、动物迁徙的生命走廊，是维护极干旱区生态系统稳定的重要组成部分。但我们对洪沟内洪水过程，植物格局与生存策略知之甚少。已有研究表明：干旱区植物格局依赖土壤水分动态，而根系分布的变化能够调节植物吸收不同深度的土壤水，从而适应不同的土壤水分变化格局。极干旱区洪沟流域上游降水较多，地表径流小且多砾石，水分保存周期短；中游干扰剧烈，但水分补给充分；下游降水极少且洪水到达的频率低，但土壤保水性较好。在此环境下，植被格局与其稳定生存的策略一直未见报道。为此，我们选择敦煌外围崔木土沟为研究对象，将通过群落调查和洪水频率、分布、下渗与土壤水分的长期监测，获取流域内洪水-土壤水-植被格局的耦合关系；通过测定不同土壤水分动态环境下洪沟不同位置优势物种茎干液流特征，获取植物稳定生存的水分利用策略。该研究将进一步完善干旱区生态水文学研究，为丝绸之路经济带建设服务。

崔木土沟植物逐水而居，物种组成单一，海拔分异显著。流域植被生长区以风沙土为主，土壤贫瘠、呈弱碱性。崔木土沟土壤水分通常不足20%，表层土壤20cm内通常不足5%，全部土层水分含量具有明显的季节波动，同时仅在洪水漫过监测点后，100cm以上的土壤含水率显著增加。河道内部，洪水发生时，水分渗漏迅速，且水分渗漏速率随土壤水分含量增加呈指数增加趋势。崔木土沟多年平均径流量为595.6万立方米，洪水为49.5万立方米，洪水流量约占总径流量的8.3 %；崔木土沟泉水流量较为稳定，洪水主要来至于夏季降水。胡杨、柽柳是崔木土沟典型代表性植物。生长季节日胡杨液流速率为5.265 cm·h-1，柽柳2.334cm·h-1。胡杨日径流呈单峰，没有明显的“午休”现象，而柽柳日径流速率在不同季节性呈现单峰、双峰或多峰的分布格局；胡杨与柽柳的径流速率与辐射、温度、风速、土壤水分含量呈现显著的正相关关系，与空气湿度呈显著的负相关关系；同时径流速率随环境因子变化具有一定的时滞性，对空气温度、空气相对湿度、风速、饱和水气压差的日变化响应呈顺时针环状；另外，整个观测期内，没有数据显示茎干液流速率变化与洪水或泉水补给具有直接的相关关系。