| Studying alpine grassland community and soil physical-chemical properties change rules in desertification process was of importance to prevent and restore grassland desertification. The paper used line transect and quadrat to research alpine grassland vegetation and soil characters varied with desertification process in Hongyuan, Sichuan province.4 line transects,6 quadrats on each line:Swamp (S), transition region between swamp and meadow (SM), Meadow (M), Slight Desertification (SD), Moderate Desertification (MD), and Heavy Desertification (HD). We got the follow results through phytocoenology survey and soil physical-chemical analysis.(1)Alpine grassland species composition significantly changed in desertification progress intensified. Richness and Shannon-Wiener diversity index increased and decreased, richness was maximum in M. Simpson diversity index and Peilou evenness added then maintained steady, Simpson diversity index positively associated with Peilou evenness. Meanwhile, desertification progress intensified lowered grassland community vegetation density, coverage, above ground biomass and underground biomass,20-40 cm underground biomass was 17805.46±7635.396 kghm-2 in S. Furthermore, vegetation density (Y) positively associated with coverage (X), Y=-214.469+X*14.043(R2=0.780, P<0.05) in desertification progress intensified. Finally, biomass carbon density which including above ground and underground biomass in each layer carbon density reduced with desertification progress intensified. Above ground biomass carbon density fitting was good to above ground biomass, to underground biomass and soil water content in 20-40 cm. Regression coefficient was 0.994 (F=654.572) and 1.000(F=3971.431), respectively. Consequently, it was bad to enhancing vegetation density, coverage, biomass and biomass carbon density in desertification progress.(2)At the aspects of soil physical-chemical, soil bulk density increased in desertifica-tion progress, minimum in S (0.95-1.00 g·cm-), and maximum in HD (1.42-1.44 g·cm-3). Meanwhile, soil water content, soil organic matter, total nitrogen and total phosphorus decreased in desertification progress. Maximum soil water and nutrient in S, and minimum soil water content and nutrient in HD. Soil water content approximately decreased from 50% to 7%, soil organic matter reduced from 2.2% to 0.2%, total nitrogen from 0.11% to 0.01, rate of reducing was smaller, from 0.15% to 0.10%. Soil bulk density in the layer of 20-40 cm (Y1) and 40-60 cm (Y2) were negative correlation with above ground biomass, Y1=0.844-X*4.769*10-6(R2=0.844)P<0.05),Y2=1.427-X*5.332*10-6(R2=0.898,P<0.05). But soil organic matter positively associated with soil water content, coverage, vegetation density, soil carbon density was fitting good with soil organic matter and underground biomass. And the best fitting was 20-40 cm soil carbon density with soil organic matter (XI), underground biomass (X2) in the same layer, Y=1925.824+X1*16961.026-X2*0.663 (R2=0.999, F=l 417.193, P<0.01). Hence, alpine grassland desertification was a process of soil texture coarse graining, soil water aridification, soil nutrient impoverishment, along with soil carbon sequestration capacity decreased.(3)Carbon density of alpine grassland reduced with biomass and soil carbon density decreased from 82621.91 kg·hm2 (S) to 5485.50 kg-hm"2 (HD). Carbon density positively associated with richness, vegetation density, above ground biomass,0-60 cm underground biomass carbon,40-60 cm soil organic matter and 0-60 cm soil carbon density, especially, it was best fitting with 0-60 cm soil carbon density, Y=-1392.481+X* 1.159 (R2=0.997, F=1289.929,P<0.01).Consequently, it changed species composition in desertification progress intensified, decreased vegetation density, coverage, biomass and its carbon density, including above ground and underground biomass. Meanwhile, soil bulk density increased and soil organic matter, total nitrogen, total phosphorus and soil carbon density reduced in desertification progress. Finally, carbon density reduced among above ground biomass, underground biomass, and soil, led to decreased alpine grassland ecological system carbon density. |
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