半干旱沙地植物生长对降雨增减变化的响应及适应机制

Precipitation is one of the critical factor in restricting plant growth, plant density, species number, and plant distribution pattern in semi-arid sandy land. The changes of precipitation process and pattern play important role in affecting the growth characteristics and the physiological processes of sandy plants, such as water absorption, photosynthesis, respiration, and metabolism. However,little is known about the response and adaptive mechanism of plant growth to precipitation changes in semi-arid sandy land, to further our understanding the problem of plant growth process in this region, there is a clear need to analysis the adaptive mechanism of plant to precipitation changes in semi-arid sandy land. The experiment will be carried out in three kinds of sandy land ( fixed, semi-fiexd, and semi-mobile) by using the rainfall-control device. The contents include (1) the relations between the process of soil moisture and plant growth under precipitation changes, (2) the effect of precipitation changes on eco-physiological characteristics of plants in semi-arid sandy land, and (3) The adaptive mechanism of plant physiological ecology response to precipitation changes. Through continuous rainfall experiments, the relations among the precipitation changes, the processes of soil moisture and plant growth will be confirmed. The response eco-physiological characteristics from individual plant to plant community to precipitation changes will be clarified. The precipitation threshold value of positive and reverse evolution on plant community will be explored. The evolution process and adaptive mechanism of plant physiological ecology response to precipitation changes will be revealed. This study will provide scientific evidence for desertification control and vegetation restoration, and predict the trend of vegetation evolution in semi-arid sandy land under climate change.

降水是半干旱沙地植物生长发育最主要的生态制约因子，降水过程与格局的改变对沙地植物的生长特征以及水分、光合、呼吸和物质代谢等生理过程都有重要影响。而关于半干旱沙地植物生长对降水特征变化的响应及适应机制的研究还相对比较缺乏。针对这一现状，本项目以科尔沁固定、半固定和半流动沙地为试验样地，应用野外增减雨装置开展控制试验。研究内容包括:（1）降雨变化条件下的沙地土壤水分过程与植被生长的关系；（2）降雨变化对沙地植物生理生态特征的影响；（3）沙地植物响应降雨变化的生长过程及生理生态学适应机制。通过本研究明确半干旱沙地降雨和土壤水分过程与植被生长的关系；探讨沙地植物群落正向和逆向演变的降水阈值；阐明沙地植物从个体到群落响应降雨变化的生理生态学变化特征；揭示沙地植被响应降雨特征变化的演变过程及其生理生态学适应机制；从而为半干旱沙地沙漠化防治、植被恢复以及未来气候变化背景下沙地植被的演变预测提供科学依据。

降雨变化对半干旱沙地植物生长和群落结构有重要影响，深入研究半干旱沙地植物响应降雨变化的生理生态学变化特征及适应机制，对沙地植被恢复以及演变预测具有重要意义。项目以科尔沁沙地为研究区域，围绕降雨格局变化，通过降雨增减控制试验，开展了沙地土壤水分，植物生长对降雨变化的响应研究。结果显示：1）科尔沁沙地降雨格局变化对一年生植物的影响更为显著，8mm降雨对一年生植物种子萌发是关键阈值。降雨总量决定了沙地能完成生活史的一年生植被数量，生物多样性不是由年降雨量决定，而是由每次降雨量与降雨次数的分布共同决定的；2）短期极端干旱对一年生植物群落生产力、生物量比、盖度、物种丰富度和根垂直分布均有显著影响。一年生植物群落地下/地上生物量比随极端干旱事件延长而增加。说明沙地植物根系生物量增加是适应极端干旱的重要机制；3）总降雨量不变，降雨次数减小、单次降雨强度增加和降雨间隔期延长的极端降雨类型显著影响一年生植物群落的地上生物量、盖度、高度、密度、生物多样性和地下生物量的垂直分布；4）随着降雨量增加，沙地植物平均高度和盖度增加，物种数降低，地上地下生物量增大，但对多样性和均匀度没有显著影响。沙地植物随多年降水增减变化呈现由1年生向多年生植物演变的趋势；5）13.4mm的降雨是流动沙地土壤有效和无效降水的关键阈值。≤5 mm的降雨只能增加表层土壤水分，0-100 cm土壤水分与降雨量显著相关，0-40 cm土壤水分与降雨强度显著相关。连续小降水事件对深层土壤水分补给有一定贡献，也是一年生植物赖以生存的主要水源。小叶锦鸡儿灌丛下0-100 cm深度土壤水分与降雨量显著相关。连续小降雨事件存在累积效应，能增加深层渗漏补给量。深层补给系数随小叶锦鸡儿种植年限增长而逐渐降低，从而影响了深层土壤水补给乃至地下水的补给。项目执行期间，共发表研究论文19篇，其中SCI收录9篇，国内核心期刊收录10篇；授权发明专利1项，实用新型专利4项。培养博士研究生2名，硕士研究生2名。