Characteristics Of Carbon And Water Use Efficiency Of Terrestrial Ecosystem In Ningxia Based On Remote Sensing

Carbon and Water Use Efficiency include Carbon Use Efficiency(CUE)and Water Use Efficiency(WUE).CUE can reflect the ability of vegetation ecosystem to convert atmospheric C02 into biomass through photosynthesis,and can also evaluate the impact of respiration on gross primary productivity.WUE is an important indicator to characterize the coupling process between carbon and water cycle in terrestrial ecosystem.Ningxia ecological system is complex and diverse,mainly include farmland,grassland,forest,settlement,desert,water and wetland,other ecosystems.In the past decade,in central and southern of Ningxia,Ecological restoration engineering like "return the grain plots to forestry and return grazing land to grassland" were implemented.Such as northern irrigation area also in adjustment of agricultural industrial structure and optimization of planting structure,this is largely changed the land cover types and the region ecosystem structure,lead to ecosystem carbon accumulation capacity and water cycle process changed However,what are the characteristics of CUE and WUE in different ecosystems on a regional scale and how they have changed in recent decades is still unclear.Therefore,in this paper,based on spatial data such as MODIS data and ecosystem type data,using spatiotemporal analysis of remote sensing and GIS to discuss the influencing factors of their spatial and temporal changes.The main results are as follows:(1)At the annual scale,the CUE of Ningxia terrestrial ecosystem was significantly and negatively correlated with the respiration consumption of plants in the region(R=-0.959,P<0.01),both the total primary productivity of the vegetation(R=-0.88,P<0.01)and the precipitation(R=-0.84,P<0.01)showed a significant negative correlation.WUE were significantly positive correlated with ET(P<0.05),and extremely significantly positive correlated with NPP(P<0.01),which is related to the seasonal growth of vegetation during the year.At the annual time scale,there is extremely a significant negative correlation(P<0.01)between WUE and Evapotranspiration(ET)in Ningxia terrestrial ecosystem,but has no correlation with net primary production(NPP).(2)The annual average of CUE in the terrestrial ecosystem of the whole region is 0.78,and the range is between 0.46 and 0.86,CUE distribution presents spatial heterogeneity.CUE varies greatly in different ecosystems.In the same ecosystem,does not necessarily the higher the plant biomass and coverage of sub-category the higher CUE especially in sub-ecosystems of grassland and woodland,the biomass and coverage has an inverse proportion with their CUE.Ningxia terrestrial ecosystem showed a bimodal shape during the year,and there was a downward trend from years.(3)The factors affecting CUE of different ecosystems during the growing season are different.Excluding the effect of plant respiration,GPP is the greatest factor impact on grassland,desert,settlement and other ecosystems.For farmland,forest,water and wetland ecosystems,it is ET,while for other ecosystems,precipitation is the biggest factor affecting CUE.(4)The average annual WUE of terrestrial ecosystems in the whole region was 1.03 g·C/kg·H20,the range was between 0.55-2.98 g C/kg H20,the higher WUE level distributed in the terrestrial ecosystems in north and south of Ningxia province,the lower WUE level mainly in the terrestrial ecosystems in middle of Ningxia province.The WUE of different ecosystems varies greatly.Sort from high to low in WUE value,it is water and wetland ecosystem,forest ecosystem,farmland ecosystem,grassland ecosystem,settlement ecosystem,desert ecosystem and other ecosystem.In the same ecosystem,the higher the vegetation biomass and coverage of the sub ecosystem,the higher the WUE.The annual WUE has a decreasing trend of 0.0141 g·C/kg H20·per year from 2000 to 2017,the monthly WUE shows a typical single peak shape during a year with a range of 0.02-2.16 g·C/kg H20 in Ningxia terrestrial ecosystem.(5)According to the strength of ET and the level of WUE,the characteristics of water use efficiency of Ningxia terrestrial ecosystem can be divided into four types,they are low ET with low WUE,low ET with high WUE,high ET with low WUE and high ET with high WUE.The ecological restoration projects implemented in Ningxia province not only enhanced the vegetation productivity,but also enhanced the regional water consumption,which decreased the water use efficiency of the terrestrial ecosystem.The conclusion of this paper could provides scientific basis for water resources utilization and ecological restoration in Ningxia province in the future.