Studies On The Plant Nitrogen Reserves And Soil Nitrogen Cycling In Kubqi Desert

The nitrogen cycling in the ecosystem and global change are closelycorrelated, while global change has an important influence on landdesertification. In this article, the plant biomass, plant nitrogen reserves andsoil nitrogen cycling in enclosed protection plot, free grazing plot and plantedalfalfa in the east of Kubqi Desert are studied, and the variations,characteristics and factors of plant biomass, plant nitrogen reserves and soilnitrogen cycling are also analyzed. The results are as follows:1. Underground biomass is more than aboveground biomass in threesandy lands. The total biomass of plant community: planted alfalfa> enclosedprotection plot> free grazing plot. The total biomass of plant community inplanted alfalfa has significant differences with the total biomass of plantcommunity in enclosed protection plot or free grazing plot. But there is nosignificant difference between enclosed protection plot and free grazing plot.2. Nitrogen content of Artemisia ordosica organ: leaves> fruits> newbranches> old branches> roots. Nitrogen content of Medicago sativa organ:fruits> leaves>flowers> stalks> roots. The nitrogen reserves of plant: plantedalfalfa> enclosed protection plot> free grazing plot. The nitrogen reserves ofsoil: planted alfalfa> free grazing plot> enclosed protection plot. The totalnitrogen reserves of plant community: planted alfalfa> free grazing plot>enclosed protection plot. The analysis of difference shows that there aresignificant differences among the three sandy lands in total nitrogen reservesof plant community.3. The soil gross nitrification rates: planted alfalfa> free grazing plot>enclosed protection plot; the soil denitrification rates: free grazing plot>enclosed protection plot> planted alfalfa. The seasonal variations of soil grossnitrification and denitrification rates of the three are relatively similar, and the highest value on gross nitrification rates is in August while denitrification rateis in July. The most obvious seasonal fluctuation on denitrification rates is infree grazing plot. There are significant effects between soil gross nitrificationand denitrification rates and soil gross nitrification rates are greater thandenitrification rates in three sandy lands.4. There are significant correlations between soil gross nitrification rates,soil water content and total soil nitrogen in enclosed protection plot and freegrazing plot. While other factors have no significant effects on soil grossnitrification rates, and also no significant correlations between soil grossnitrification rates and all factors in planted alfalfa. The soil temperature hassignificantly positive correlation on denitrification rates. Similar to it, the fineroot biomass also has significantly positive relationship with denitrificationrates in enclosed protection plot and free grazing plot. This indicated that soiltemperature is the primary factor on denitrification in Kubqi Desert.5. The denitrification rate in enclosed protection plot has significantnegative correlation with plant nitrogen reserves. While there is no significantcorrelation with soil nitrogen reserves and total nitrogen reserves of plantcommunity. Its equation of linear regression is y=-0.0904x+8.2434(R2=0.7902，P<0.05). The nitrification rate in free grazing plot has significantpositive correlation with soil nitrogen reserves and total nitrogen reserves ofplant community. But it is no significant correlation with plant nitrogenreserves. Their equations of linear regression are y=0.7654x+88.549(R~2=0.8062，P<0.05)and y=0.8138x+91.705(R~2=0.7581，P<0.05).