毛乌素典型固沙植物的水分利用特性与吸水机制

Water use characteristics and the mechanism of water uptake in two typical sand-fixing species in Mu Us sandy land

了解固沙植物的吸水机制有利于合理设置植被群落结构,可为科学治沙和水资源高效利用提供依据。本研究基于降水-土壤水-植物木质部水-地下水的氢氧同位素组成,结合土壤水热和植被全年耗水特征,利用多源线性混合模型(IsoSource),分析了冬季和生长季典型沙地植物沙柳和沙蒿的水分来源差异,并探究了地下水位埋深(2和10 m)、土壤冻融和干旱对其水分利用的影响。结果表明:1)沙柳在土壤冻融期(1-3月)主要利用冻层下60~120 cm深度土壤水(69.1%);在返青季(4、5月)0~60 cm层土壤水可满足生长需求(30.9%~87.6%);在生长季的干旱期(6月)主要利用120~160 cm层土壤水(27.4%~40.8%);而在雨季(7、9月)0~60 cm层土壤水对其供水达到59.8%~67.9%。根系较浅的沙蒿在根区土壤完全冻结后无法利用土壤水,可通过秋季储存在根茎的水分越冬;而在生长季以利用0~40 cm层土壤水为主(23.4%~86.8%),在旱期主要利用40~80和80~160 cm层土壤水,利用率分别为14.6%~74.4%和21.8%~78.2%。2)随着地下水埋深的减小,植被吸取土壤水的深度上移,其中沙柳水分来源由120~160 cm层土壤水向60~160 cm层变化,而沙蒿的吸水深度从80~160 cm层变为0~40 cm层。沙柳对土壤水的利用受植物蒸腾的影响,会“按需取用”以达到供水与节能的平衡;沙蒿则偏向利用浅层土壤水,对单一土壤层位的水源依赖较高。

Understanding water absorption mechanisms of sand-fixing plants is important for the rational establishment of plant community structures,thereby providing a scientific basis for desertification control and the efficient utilization of water resources in sandy areas.Based on the hydrogen and oxygen isotopic compositions of precipitation,soil water,xylem water,and groundwater,coupled with soil water-heat dynamics,annual water consumption characteristics of vegetation,using the multi-source linear mixing model(IsoSource),we analyzed the differences in water sources between Salix psammophila and Artemisia ordosica,during winter and the growing season.We further examined the effects of groundwater depth(2 m and 10 m),soil freezing-thawing,and drought on their water utilization to elucidate water absorption mechanisms of those species.The results showed that:1)During soil freezing-thawing period(January to March),S.psammophila mainly utilized soil water in 60-120 cm depths below the frozen layer(69.1%).In the green-up season(April and May),soil water from the 0-60 cm layers could satisfy the water demand of S.psammophila(30.9%-87.6%).During the dry period of the growing season(June),it predominantly utilized soil water at the depth of 120-160 cm(27.4%-40.8%).Over the rainy season(July and September),soil water in 0-60 cm depths provided 59.8%-67.9% of the total water required.A.ordosica,with shallow roots,could not utilize soil water after complete freezing of root zone but could overwinter by storing water in rhizomes during autumn.During the growing season,it primarily relied on 0-40 cm soil layer(23.4%-86.8%).During the dry period,it mainly utilized soil water from 40-80 cm and 80-160 cm soil layers,with utilization rates of 14.6%-74.4%and 21.8%-78.2%,respectively.2)With decreasing groundwater depth,vegetation shifted its water absorption depth upward,with water source of S.psammophila transitioning from 120-160 cm to 60-160 cm layers,while A.ordosica shifted water absorption depth from 80-160 cm to 0-40 cm.S.psammophila's utilization of soil water is influenced by transpiration,adopting an"on-demand"approach to achieve a balance between water supply and energy conservation,whereas A.ordosica tends to utilize shallow soil water,exhibiting a higher dependence on water sources from a single soil layer.