藏北那曲地区草地退化动态评价

利用1982—2000年NOAA/AVHRR 第1通道、第2通道和NDVI的旬资料反演得到的藏北那曲地区历年植被覆盖度、年最大牧草鲜质量和6—9月平均改进型土壤调节植被指数，分析了近20年来那曲地区草地荒漠化的动态变化规律.结果表明：以草地荒漠化评价“基准”和5年滑动平均的方法，得到那曲地区近20年平均草地退化面积占土地总面积的43.1%，草地退化面积总体呈减少趋势，其中前10年呈减少趋势，后10年呈增加趋势，西部地区的退化面积大于其它地区.在气温、降水、潜在蒸散、水汽压、风速、日照时数、降水蒸散比和温度降水比8个气候因子中，潜在蒸散量对草地退化面积的影响最显著.

Effects of Pb and Zn stress on Trichosanthes kirilowii seedlings growth and stress-resistance physiological factors

The study with pot experiment showed that under Pb and Zn stress,the biomass of Trichosanthes kirilowii seedlings decreased,their plant dwarfed,and the number of leaves with yellow spots increased.Pb had greater effects on the seedlings growth than Zn.With increasing concentration of Pb,the contents of photosynthetic pigments increased first and decreased then,but increasing concentration of Zn had lesser effects on them.The contents of UV-B absorbing compounds and the activities of superoxide dismutase(SOD)and peroxidase(POD)increased while soluble protein and saccharide contents decreased with the increase of Pb and Zn concentrations.T.kirilowii seedlings had definite tolerance to Pb and Zn stress,but their growth and stress-resistance physiological factors were inhibited to a greater extent when the Pb and Zn concentrations were higher.