昼夜增温对南四湖湿地植被NDVI的影响差异

利用近40 a的Landsat系列卫星的MSS、TM和ETM+遥感数据，计算了南四湖湿地植被平均归一化植被指数（NDVI），并以此为湿地植被活动的指标，结合南四湖流域内气象站点的逐年、逐月及逐日气温数据，揭示昼夜温度变化对湿地植被活动的影响差异。结果表明：1）近40 a来研究区日最高温（T_max）、夜间最低温（T_min）和日均温（T_ave）都存在显著的上升趋势；其中T_max与T_min增温具有不对称性，R²值分别为0.13和0.26，平均每10 a分别增温0.174℃和0.235℃，T_min的增温趋势更明显。2）在人为活动影响较弱的时段（1973―1999年），偏相关分析显示，去除Tmin影响，T_max与NDVI呈现极显著的偏相关关系（R＝0.412，P＝0.008）；去除T_max的影响，T_min与NDVI的偏相关关系在任何时期内均不显著。这可能与湿地充足的水份条件以及昼夜增温对湿地植被的生态效应不同有关。

Effects of Air Temperature Circadian on theNDVIof Nansi Lake Wetland Vegetation

The normalized difference vegetation index (NDVI) of the Nansi Lake wetland vegetation in Shandong province were calculated on the basis of MSS, TM and ETM+ remote sensing data collected by the Landsat satellites. The main meteorological factors which influence wetland vegetation activities were deduced by NDVI. And combined with meteorological data in the study area, the asymmetric effects of daytime and nighttime air temperature on wetland vegetation were revealed. The results are as follows: 1) In the past 40 years, T_max, T_min and T_ave have been increased in Nansi Lake wetland. The change feature betweenT_maxand Tmin (R²＝0.13 and 0.26 respectively) was different and increased 0.174℃ and 0.235℃ respectively. The change tendency ofT_min was more significant. 2) If the human influences were removed, the asymmetric effects of circadian air temperature on wetland vegetation would be quite obvious. The wetland NDVI increased significantly with the increase ofT_max, and had no correlation withT_min . This may be related to wetland adequate moisture and ecological effect of wetland vegetation caused by circadian air temperature. This study may have important reference for understanding vegetation response characteristic to air temperature in different ecosystems.