Preliminary Research on Grassland Fine-classification Based on MODIS

Abstract

Abstract. Grassland ecosystem is important for climatic regulation, maintaining the soil and water. Research on the grassland monitoring method could provide effective reference for grassland resource investigation. In this study, we used the vegetation index method for grassland classification. There are several types of climate in China. Therefore, we need to use China's Main Climate Zone Maps and divide the study region into four climate zones. Based on grassland classification system of the first nation-wide grass resource survey in China, we established a new grassland classification system which is only suitable for this research. We used MODIS images as the basic data resources, and use the expert classifier method to perform grassland classification. Based on the1:1,000,000 Grassland Resource Map of China, we obtained the basic distribution of all the grassland types and selected 20 samples evenly distributed in each type, then used NDVI/EVI product to summarize different spectral features of different grassland types. Finally, we introduced other classification auxiliary data, such as elevation, accumulate temperature (AT), humidity index (HI) and rainfall. China's nation-wide grassland classification map is resulted by merging the grassland in different climate zone. The overall classification accuracy is 60.4%. The result indicated that expert classifier is proper for national wide grassland classification, but the classification accuracy need to be improved.

Nitrogen-cycling microbial communities respond differently to nitrogen addition under two contrasting grassland soil types

“…In natural ecosystems, soil nitrogen conversion is primarily driven by nitrification during the early growth seasons, while ammonium conversion becomes more prominent toward the end and non-growth seasons ( Liu and Ma, 2021 ). Notably, the end of the growing season occurs later in warm-temperate shrubs compared with temperate steppes ( Lee et al, 2002 ; Hu et al, 2014 ). In this study, the rate of soil N mineralization in the temperate steppe was significantly and positively correlated with the ammonification rate, while it showed a stronger positive correlation with the nitrification rate in the warm-temperate shrub, demonstrating that the warm-temperate shrub had a stronger nitrification process than the temperate steppe ( p < 0.01, Figure 5 ).…”