| The community characteristics and plant diversity(?,? and ? diversity)in different growth seasons(May,July and September),and carbon,nitrogen storages in plant,soil and ecosystem in sagebrush desert on northern slope of Tianshan Mountains were measured.RDA redundancy analysis,structural equation model(SEM)and regression analysis method were used,which amied to clarify the spatial and/or temporal variability of biomass,plant diversity and carbon,nitrogen storage,and analyze the dominant environment factors affecting the difference of biomass,diversity,carbon and nitrogen storages,and explore the relationship among biomass,diversity and carbon/nitrogen storages.The results can provide a theoretical basis for the maintenance of biodiversity,carbon and nitrogen storages in grassland ecosystem,and provide some basic informations for the scientific management of desert grassland.Some conclusions can be drawn as follows:(1)Above-and below-ground biomass(AGB and BGB)and total biomass decreased gradually from west to east.Above-ground biomass increased gradually with the increase of precipitation,but the influence of environmental factors on underground biomass and total biomass were relatively weak.(2)The Patrick richness index(R),Simpson dominance index(D)and Shannon-Wiener diversity index(H)gradually decreased from May to September,and they in September decreased by 52.2%?63.8%,31.0%?48.9%and 43.7%?58.9%than that in May,respectively.In east section,the R,D and H lower significantly 30.7%?41.5%,10.5%?33.7%and 21.1%?42.4%than west section,respectively(P<0.05).GE decreased significantly the R,D and H by 12.7%?52.1%,18.6%?71.6%and 21.7%?70.5%(P<0.05)in west section.However,the R,D and H in middle section decreased remarkly only in a few months,and the response of R,D and H in east section to GE were weak.Moreover,the R has a linear positive correlation with mean annual precipitation(MAP)and a quadratic function with mean annual temperature(MAT).(3)In northern slope of Tianshan Mountain,the carbon and nitrogen storages in in ecosystem(included the AGB,BGB,litter,and soil)were 6678.6 g·m-2?8787.8 g·m-2 and 856.3 g·m-2?1139.3 g·m-2.The carbon and nitrogen storages of above-ground biomass,soil and ecosystem have a close linear positive correlation with MAP.(4)In sagebrush desert on the northern slope of Tianshan Mountains,the richness index,soil organic carbon and total nitrogen contents and storages,underground plants nitrogen storages and ecosystem carbon and nitrogen storages decreased significantly after short-term grazing exclusiom(P<0.05),but in the middle and West section,aboveground biomass and its carbon and nitrogen storages increased significantly after grazing exclusion,while the nitrogen storage in underground plants and soil decreased significantly in the middle section.(5)SEM and RDA analysis showed that plant coverage and soil moisture content(MC)were the main driving factors of biomass variation in sagebrush desert,while soil MC and underground biomass were the main driving factors of plant diversity variation.The spatial variation of carbon storage in ecosystem were mainly controlled by MAP and pH,and the variation of nitrogen storage in ecosystem was mainly controlled by MAP.In addition,biomass and plant diversity,ecosystem carbon and nitrogen reserves were closely related,but the relationship between plant diversity and ecosystem carbon and nitrogen reserves were weak.The above results show that the biomass,plant diversity and carbon and nitrogen storages of sagebrush desert on the northern slope of Tianshan Mountains have great spatial variability,and the short-term grazing exclusion effect of the degraded sagebrush desert in the middle and west section was better,and improvement measures such as supplementary sowing and fertilization should be taken to accelerate desert restoration,and to maintain the health and stability of desert ecosystem. |
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