Study On Grassland Degeneration Based On Ecological Stoichiometry

Jiangjiadian meadow of Da’an city locates at the low plain in the middle of SongnenPlain. The entironment here is weaker. In recent years, influenced by global changing andhuman reason, the grassland area is reducing gradually; meanwhile, vegetation coveragelevel is depressing. Desertification, salinization and degeneration of the grassland aremore serious and its entironment is getting worse. All these have restricted thedeveloping of local society and economy. The research of grassland degenerationquestion in this area has important meaning to protecting grassland resource scientifically,to controlling grassland degeneration, and to repairing grassland entironment.This paper takes Plant-Soil as a system to research. Based on ecologicalstoichiometry and element theory of constraints, using software such as SPSS and Matlab,I analyzed the interaction between the ecological chemical measurement features of C, Nand P in L. chinensis leaves and soil element and its chemical character. Using RBFArtificial Neural Networks （ANNs）, I built the forecast model of the content of C,N andP elements in L. chinensis leaves.Using K value clustering analysis method, Ianalyze thedegeneration level of the grassland. After that, I analyze the soil chemistry character ofdifferent degeneration levels, and ecological chemical measurement features of L.chinensis leaves. The result of the research proves:1. The contents of soil gein and TotalN in research area are all lower than nationalaverage. Compared with national second time soil survey standard, the contents of soilgein and TotalN belong to middle third level, and the content of soil TotalP belongs to extremely poor level (lower than0.4mg·g^-1). In the soil, the value of C/N, C/P and N/Pare9.81、41.72、4.39, all lower than national average. The contents of available N andavailable P are poor, available K is richer. There are both a soil salinization and alkalineexistence. Soluble salt and alkaline level show significant negative correlation with thecontent of soil nutrient elements.2. The contents of C, N and P in L. chinensis leaves at Da’anJiangjiadian meadoware443.75mg·g^-1、18.70mg·g^-1、1.30mg·g^-1. They are all lower than global averagecontents in terraneous plant leaves (464mg·g^-1、20.6mg·g^-1、2.0mg·g^-1). And thecontent of N and P are even lower than national data. The space difference of CinL.chinensis leaves is obviously lower than N and P. The values of C/N, C/P and N/P inL.chinensis leaves are all higher than those in global terrestrial plant leaves. InL.chinensis leaves,14＜N/P＜16. The growth of L.chinensis in research area islimited by both N and P.The content of N and P show significant positive correlation; Thecontent of C inleaves show significant positive correlation with content of C, N, P andavailable P in soil. There is no significant correlation between the content of N in leavesand C, N, P in soil.3. Based on the principle of ANNs, I take soil nutrient elements and relevantchemistry character as input layer. The contents of C, N and P in L. chinensis leaves areregarded as output layer. It’s feasible to create RBF ANNS model with Matlab and use itfor calculate the interaction between the contents of C, N and P in L. chinensis leaves andsoil chemical nature. After checking, the relative error is within20%. The forecastingaccuracy is higher.4. Through K value clustering analysis method, using soil and plants as index, Idivide the85sampling points in research area into four types of degeneration level. Andconfirm the grassland degeneration level combined with the physical truth of field survey.The result shows that in research area, grassland of low-grade degeneration takes5.88%,mid-grade takes9.41%, high-grade takes35.29, and extremely high-grade takes49.41%.The regeneration of grassland in research area is severe.5. With the aggravation of grassland degeneration degree, the contents of TotalC and TotalN get lower gradually, but the changing of TotalP content is smaller. As a whole,the values of C/N, C/P and N/P all show decreasing trends. In different degenerationlevels, the content sequence of available N in L. chinensis leaves is mid-grade＞low-grade＞high-grade＞extremely high-grade. The content of available P declinesgradually with the aggravation of grassland degeneration degree. And at the same time,the content of available K declines sharply from low-grade of degeneration(214.98mg·kg^-1)to mid-grade (144.63mg·kg^-1), then remains comparatively steady.PH, total soluble salt and basification degree ratchet up with the aggravation of grasslanddegeneration. Grassland degradation degreeand soil salinity level condition is correlated.6. In different degeneration levels, the content sequenceof C in L. chinensis leavesis mid-grade＞low-grade＞high-grade＞extremely high-grade.The content sequenceof Nis mid-grade＞extremely high-grade＞low-grade＞high-grade. Except extremelyhigh-grade degeneration stage, the variation trend of N in leaves is same as available N.The content of P in L. chinensis leaves shows decrease then increase. C/N value declineswavily. In low-grade degeneration stage, the growth of L. chinensis is limited both by Nand P. In mid-grade degeneration stage, it is limited mainly by P. In high-grade andextremely high-grade degeneration stages, it is limited mainly by N. Except nutrientelement, the growth speed of L. chinensis is still influenced by other soil physical andchemical properties.