河西走廊荒漠区沙拐枣种群扩张过程及其对降水的响应机制

Rainfall is a central factor in water-limited arid desert ecosystem, whose pattern and intensity may have an important impact on population expansion in desert plants. How desert plants successful planting in sand dune by rainfall is a scientific problem to be solved. Precipitation not only affects the distribution of desert vegetation and growth, also controls the spatial expansion of desert plant population. However, quantitative study on how precipitation process affects the desert plant species invasion, establishment and spatial expansion has been not fully understood. In this study, we used a typical desert shrubs Calligonum mongolicum in arid regions in Hexi Corridor of Gansu province as a research subject. By means of field investigations, multi-scale manipulations, laboratory experiments, and theoretical analysis, we would explore three key questions: (1) the reproduction strategy, trade-off between clonal and sexual reproduction of Calligonum mongolicum in sand dune of arid region. (2) The responses of Calligonum mongolicum population expansion to natural precipitation process. (3) The effects of simulated precipitation and drought stress on Calligonum mongolicum rhizome extension and ramet growth. (4) The possible mechanisms underlying how precipitation patterns affect Calligonum mongolicum population expansion. Our aims of this study are to understand the influence rules of precipitation process on population expansion, to reveal the invasion and expansion strategy of typical plant species in sand dune desert ecosystem, to determine the expansion rate and adapting strategy. The findings may promote deeply the interaction study of ecohydrology.

荒漠植物如何利用降水在沙丘上成功定植是干旱区生态环境建设中亟待解决的科学问题。降水不仅影响着荒漠植被的分布与生长，也控制着荒漠植物种群的扩张。但关于降水过程如何影响荒漠植物种群的侵入、定居和扩张的定量研究一直是荒漠生态学研究中仍然没有很好解决的问题之一。本项目以甘肃河西走廊干旱区典型荒漠植物沙拐枣为研究对象，通过野外自然生境监测和野外控制实验相结合的方法，开展干旱荒漠区沙丘生境沙拐枣种群的繁殖方式和繁殖权衡、沙拐枣种群扩张过程对自然降水的响应、模拟增雨与干旱胁迫对沙拐枣根茎扩展和分株生长的影响，以及降水格局变化影响沙拐枣种群扩张机制研究，旨在认识干旱区降水过程对种群扩张过程的影响规律，揭示荒漠生态系统典型植物种群在沙丘上侵入与扩张方式，确定扩张速率及适应对策，促进干旱区生态水文相互作用研究的深入。

荒漠沙丘典型固沙植物沙拐枣通常以有性和无性两种繁殖方式侵入定居在沙质生境中。然而，沙拐枣种群如何向周围流沙斑块扩展并定植？不同生境有性繁殖和无性繁殖如何权衡？以及降水变化如何影响其扩张过程？研究沙拐枣种群扩张过程对荒漠生态系统中种群更新、植被恢复与治理技术具有重要意义。基于以上科学问题，本项目通过野外动态监测和田间控制试验相结合的方法，阐明了不同生境沙拐枣种群繁殖方式和扩张特征，揭示了沙拐枣克隆繁殖方式对风蚀和沙埋的适应性，探讨了降水对沙拐枣种群扩张过程的影响和调节机制。取得的主要进展有：（1）在固定沙丘、半流动沙丘迎风坡、背风坡、丘间低地，沙拐枣种群无性繁殖的扩张域和平均扩张速率分别为1～5m和0.67m/a、1～8m和0.64m/a、0～2m和0.15m/a、1～4m和0.41m/a。沙拐枣种群在侵入新的生境过程中，开始于有性繁殖，利用无性繁殖拓展生存空间。（2）风蚀和沙埋显著影响沙拐枣分株的生长和繁殖能力。长期中度风蚀对沙拐枣分株的生长和繁殖有明显促进作用。沙拐枣克隆分株间的克隆整合能够很好的缓解风蚀和沙埋对沙拐枣分株生长和繁殖的抑制作用，增强其忍受风蚀和沙埋能力，通过无性繁殖利用其根茎向裸露流沙扩展，扩展到相邻流沙生境的分株通过资源共享为其在相邻流沙生境的生长以及迅速占领裸露流沙生境提供保证。（3）降水显著影响沙拐枣种群生长速率和繁殖状况。在降水量相对丰富的年份种群增长率高，沙拐枣种群通过产生大量实生苗和无性系分株来维持种群的快速扩展，但植物个体大小增长缓慢；在降水量相对较少的年份，沙拐枣通过无性繁殖产生大量分株，而靠种子萌发产生的实生苗数量较少。并且大部分新生分株在当年冬天越冬时死亡，只有少部分个体能够存活。这种新分株的大量产生和大量死亡有效实现了干旱年份分株的快速更新，从而为基株不断补充新生个体，提高干旱年份种群的存活和繁殖能力，有利于种群向周围流沙斑块扩展。