Analyses of Precipitation Pattern on southern margin of Garbantunggut desert and response of different functional type plants to small rainfall events

在干旱半干旱地区的生态系统中水是主要的限制因子，因此水分的有效性在很大程度上决定着生态系统的结构与功能。具有生物学意义的降水是干旱半干旱地区植物主要水源。而小雨量降水事件发生频次高、占降水事件的比重大，它能否被有效利用逐渐成为大家关注的焦点。本论文在野外实验的基础上，对古尔班通古特沙漠南缘降水模式和不同生活型植物对小雨量降水的生理响应进行了研究。通过分析1998-2007年的降水数据，分析结果表明，本区的降水模式为小雨量，高频率，0-5mm的小雨量降水占总降雨频次的89.8%，平均降水间隔在6 d左右。实验选取了本区具有代表性的16种植物，利用叶片相对含水量作为指标，研究了不同生活型植物对小雨量降水（1、2、3、4和5mm）的响应。结果表明，所有草本植物（11种）对2~5mm的降水都有不同程度的响应，只有1种灌木（ 驼绒藜 Ceratoides latens），对4mm降水有响应。这12种植物在降水后的第1天，叶片相对含水量显著增加（P<0.05），水分状况的到显著改善，表明这些植物对小雨量（≤5mm）降水有显著响应，而半灌木（沙漠绢蒿Seriphidium santolinum）、灌木（梭梭Haloxylon ammodendron、柽柳Tamarix ramosissima）、小乔木（白梭梭Haloxylon persicum）对5mm以下的降水均无显著响应，小雨量降水可能主要被1年生草本植物所利用。通过统计各降水梯度上响应的植物种数发现，在降水量达到3mm时开始响应的植物种类最多。综合考虑降水模式与不同生活型植物对小雨量降水的响应特点，高频率的小雨量降水，可能是维持本区较高植被覆盖度的重要原因。Water is one of the most important limited factors in the Arid and Semi-arid Areas. Effectiveness of water can affect the function of ecosystem. Ecological important rainfall is one of the water recourse in arid and semi-arid areas. Recently, more and more studies focus on the use of small rainfall events by plants. This paper studied the size characters of precipitation in south edge of Garbantunggut Desert and the responses of different life-form plants there to small rainfall events. Based on the analysis of the precipitation data in 1998-2007, the study area had a high frequency but low amount of precipitation. Rainfall events occurred every 6 days averagely, and most (89.8%) of the events were ≤5mm. Sixteen representative plant species were selected and their leaf relative water content (RWC) was used as the parameter to investigate the responses of different life-form plants in the area to small rainfall events (1、2、3、4、and 5mm). The results revealed that all 11 herb species had different degrees of responses to 2-5mm rainfall, and only one shrub species Ceratoides lateens responded to 4mm rainfall significantly .The leaf RWC of the 12 species increased significantly after one day of rainfall, suggesting that these species had significant responses to small rainfall events(≤5mm). Sub-shrub (Seriphidium santolinum), shrub(Haloxylon ammodendron, Tamarix ramosissima), and small tree (Haloxylon persicum) did not response to the rainfall events ≤5mm. Small rainfall events mainly benefited herb species, and the high frequency but low amount of rainfall partially explained the relatively high vegetation cover in this area