关键词: 森林土壤, 甲硫氨基酸, 土壤水分, 硝化作用, 氧化亚氮

Abstract: Based on MODIS NDVI remote sensing and contemporaneous weather data, we used trend analysis, coefficient of variation and Hurst index to investigate the dynamics of vegetation coverage in Ningxia from 2000 to 2016. The vegetation coverage showed an overall increasing trend over time, with a large difference between north and south. NDVI increased significantly from 2000 to 2005, relatively slowly increased from 2006 to 2011, and slightly decreased from 2012 to 2016. Precipitation and humidity index showed the greatest response to vegetation growth. In the growing season, NDVI showed an overall rising trend, with 79.88% of the study region showing significant increase in NDVI. Seasonal NDVI increased at a rate of 0.026·10 a^-1,0.07·10 a^-1 and 0.049·10 a^-1 in spring, summer and autumn respectively, during 2000-2016. Although the vegetation coverage in 62.13% of the vegetationcovered area continued to increase, some regions exhibited decreasing vegetation coverage. The continued improved area in vegetation coverage in southern forest area was larger than that in northern irrigation area around the Yellow River.

Key words: forest soil, Lmethionine, soil water, nitrification, nitrous oxide.