西双版纳石灰山热带季节性湿润林内几种植物的水分利用策略

Plant Water Use Strategies in a Limestone Tropical Seasonal Moist Rainforest in Xishuangbanna,SW China

对西双版纳生境严酷的石灰山热带季节性湿润林内几种植物（潺槁木姜子、羽叶白头树、高榕、豆果榕、清香木等）的水分利用策略进行了研究。结果表明，石灰山热带季节性湿润林内土壤水势在干热季（2月～4月）75cm深度处达到最低值，为-0．055MPa，雨季（5～10月）在30cm处出现最低值为-0．039MPa。测定不同深度土壤体积含水量昼夜变化表明，白天和夜间各层深度土壤体积含水量没有显著变化（P〉0．05），说明本林内植物没有水分再分配现象的发生。通过对雨水、土壤水、地下水、雾水、穿透水以及植物木质部水分的稳定性同位素分析得出，在干季，滴落雾水能够补给土壤表层水，在雨季，降雨则是地下水的主要水分输入。植物在昼夜尺度上虽然没有对水分进行时空区分利用，但是植物有更为长久有效的水分利用策略，即植物通过自身发达的根系统利用深层土壤水和地下水。目前，热带雨林的乱砍滥伐，森林片段化特别严重，尤其是生长在石灰山严酷生境的热带季节性湿润林受到破坏后，森林的重建和恢复是相当困难的。因此，对脆弱石灰山热带季节性湿润林的保护是十分必要的，而对石灰山热带季节性湿润林植物的水分利用方式和策略的研究将为此目标提供理论依据。

Soil water potential was detemained during April 2006 and May 2007 at a limestone tropical seasonal moist rainforest site in Xishuangbanna, Southwest China. The results indicated that soil is drier in dry season （from November to April） than in rainy season （from May to October）, especially in March and April, with soil moisture content reaching the minimum value of -0.055 MPa at 75 cm depth. While in rainy season, soil humidity situation is much better than dry season, and soil water potential can reach to 0.010 MPa. Hourly observation of soil volumetric water content on three days in November 2006, January 2007 and March 2007 showed that the difference between diurnal values and nocturnal values is not significant （ P 〉 0.05）, suggesting there is no obvious soil volumetric water content fluctuation in deferent soil depths. In other wonts, there is no hydraulic redistribution in limestone tropical seasonal moist rainforest. Intercepted fog drip and throughfaU by canopy, rainwater, soil water, groundwater and stem xylem water were collected during November 2005 and February 2007 for stable isotopic analysis. The stable hydrogen （SD） and oxygen isotope composition （δ^18O） of fog drip,throughfall, rainwater, soil water, groundwater and stem xylem water were determined from an isotope ratio mass spectrometer. The results indicated that the rainfall is the main source of soil water and groundwater in rainy season. Through the canopy, throughfall is enriched than rainwater, because of evaporated fractionation. The fog drip was thought to contain water that has been evaporated and recycled terrestrial meteoric water （evaporation of nearby surface waters and canopy interception）, so the fog drip was more enriched than rain during both the dry season and rainy season. What＇s more, although fog is heavy, plants mainly use groundwater and deep soil water in dry season in this region, hardly making use of fog drip. This result is related to the natttral environment, limestone tropical seasonal moist rainforest is very vulnerable, sothat, protect this pattern forest is necessary, further research will be able to provide a basis for this purpose.