Research On The Temporal And Spatial Changes And Influencing Factors Of Net Primary Productivity Of Grassland In Northern Xinjiang

Grassland is the most widely distributed but most vulnerable system in terrestrial ecosystems.Grassland biomass not only reflects changes in the surrounding environment,but also responds directly to climate change.Grassland Net Primary Productivity（NPP）reflects the sustainability of grassland ecosystems.An indispensable indicator for development.Xinjiang is one of the important grassland pastoral areas in China,and it carries a large number of livestock and livestock products in China.As the main distribution area of Xinjiang grassland,northern Xinjiang not only provides the material basis for animal husbandry production,but also plays an important role in the global carbon cycle.Most previous studies only considered the impact of meteorological factors on grassland NPP,but there are many factors that affect NPP changes during grassland growth.Therefore,this study takes northern Xinjiang as the research area,based on the measured grassland biomass data,using the CASA model,combined with MOD13A1 data,meteorological data,topographic data,and statistical yearbooks to retrieve the NPP of northern Xinjiang grassland from 2007 to 2016,and analyze its time and space.Change characteristics and their relationship with impact factors.The result is as follows:（1）From 2007 to 2016,the annual average NPP spatial heterogeneity of northern Xinjiang grassland is high,which is characterized by higher than that in the west,higher than the east in the west,higher in the north and south,and higher in the mountains than in the desert.The high-value areas are concentrated in the Yili River Valley,and the low-value areas are concentrated in the central arid zone,the annual average grassland NPP in northern Xinjiang is 149.87 g C·m^-2·a^-1.（2）From 2007 to 2016,the interannual NPP of grassland in northern Xinjiang showed an overall upward trend.The average annual grassland NPP in 2016 was the highest,reaching 179.18 g C·m^-2·a^-1,and the lowest in 2008 was 124.12 g C·m^-2·a^-1.The Intra-year NPP showed a gradual increase from January to June,followed by a monthly downward trend.The lowest value appeared at 0.04 g C·m^-2·a^-1 in January,and the highest value appeared at 21.42 g C·m^-2·a^-1 in June.（3）The annual average NPP of different types of grassland is quite different.The highest i s 393.97g C·m^-2·a^-1 for temperate mountain meadows,and the lowest is 56.78 g C·m^-2·a^-1 for temperate deserts.The overall performance is Meadow>Grassland>Desert Grassland.At the same time,the interannual variation characteristics of NPP of various grassland types are relatively consistent,showing an increasing trend.Temperate meadow grassland is the grassland type with the highest growth rate,with a rate of 3.41 g C·m^-2·a^-1.（4）Among the meteorological factors,the influence of precipitation on the NPP of grassland in northern Xinjiang is significantly greater than that of temperature.The overall performance of precipitation and grassland NPP is positively correlated,while NPP and temperature are generally negatively correlated.Among the topographic factors,altitude and slope have significant effects on grassland NPP.Among human activities,urban population,large livestock,sheep and primary industry have a significant impact on grassland NPP.