毛乌素沙地4种植物叶水势变化及其影响因素分析

对毛乌素沙地旱柳( Salix matsudana Koidz.)、小叶杨( Populus simonii Carr.)、北沙柳( Salix psammophila C. Wang et Chang Y. Yang)和沙蒿(Artemisia desertorum Spreng.)4种植物叶水势的月变化和日变化规律以及不同冠层叶水势的差异进行了研究,并分析了4种植物叶水势与气候因子及树干液流速度的相关性。结果表明：在5月份至8月份,旱柳、小叶杨和北沙柳清晨(5：00)的叶水势波动不明显；但3种植物正午(13：00)的叶水势有一定差异,其中旱柳和小叶杨正午的叶水势差异不明显,而北沙柳7月份和8月份的叶水势则明显小于其5月份和6月份；总体上看,各月份3种植物正午的叶水势均明显小于清晨叶水势。供试4种植物的叶水势日变化曲线均以“单峰型”为主,最高值出现在5：00至6：00,最低值出现在12：00至16：00；日间北沙柳的平均叶水势最低,而其他3种植物的平均叶水势差异不明显,5月份和8月份,北沙柳的平均叶水势分别为-11.9和-17.1 MPa,而旱柳、小叶杨和沙蒿的平均叶水势分别为-6.2和-7.1、-7.7和-7.3、-6.8和-8.4 MPa；但夜间4种植物的平均叶水势无明显变化。4种植物日间均表现出树冠下层叶水势高、上层叶水势低的趋势,而夜间则树冠上层和下层的叶水势几乎一致。相关性分析结果表明：4种植物的叶水势与气温、净辐射量以及树干液流速度负相关、与空气相对湿度正相关,其中,不同月份4种植物的叶水势与净辐射量和树干液流速度均极显著相关(P<0.01)。研究结果显示：毛乌素沙地不同植物叶水势的变化因种类、季节、气候条件的不同而异,但总体上看净辐射量是影响4种植物叶水势变化的最主要气象因子。

Analyses on change in leaf water potential of four species in Maowusu sandland and its influence ;factors

Monthly and diurnal change laws of leaf water potential of four species of Salix matsudana Koidz., Populus simonii Carr., Salix psammophila C. Wang et Chang Y. Yang and Artemisia desertorum Spreng. in Maowusu sandland and difference in leaf water potential in different crown layers were researched, and correlations of leaf water potential of four species with climatic factors and sap flow velocity were analyzed. The results show that the fluctuation of leaf water potential of S. matsudana, P. simonii and S. psammophila in the morning (5:00) from May to August is not obvious, but there is a certain difference in leaf water potential of three species at noon (13:00), in which, the difference in leaf water potential of S. matsudana and P. simonii at noon is not obvious, while leaf water potential of S. psammophila in July and August is obviously smaller than that in May and June. In general, leaf water potential of three species at noon in all months is obviously smaller than that in the morning. Diurnal change curve of leaf water potential of four species tested is main “single peak type”, the highest value appears from 5:00 to 6:00 , and the lowest value appears from 12:00 to 16:00 . Average leaf water potential of S. psammophila in the daytime is the smallest, while there is no obvious difference in average leaf water potential among other three species. In May and August, average leaf water potential of S. psammophila is -11. 9 and -17. 1 MPa, respectively, while that of S. matsudana, P. simonii and A. desertorum is -6. 2 and -7. 1, -7. 7 and -7. 3, -6. 8 and -8. 4 MPa, respectively, but that of four species in the nighttime has no obvious change. Leaf water potential of four species all appears the trend of high in lower layer and low in upper layer of crown during the daytime, while leaf water potential almost is the same in upper and lower crowns during the nighttime. The correlation analysis result shows that leaf water potential of four species has negative correlation with air temperature, net radiation and sap flow velocity, and has positive correlation with air relative humidity, in which correlations of leaf water potential of four species in different months with net radiation and sap flow velocity are obviously significant ( P<0 . 01 ) . It is suggested that leaf water potential of different species in Maowusu sandland changes with species, seasons and climatic conditions, while in general, net radiation is the most important climatic factor affecting change in leaf water potential of four species.