Leaf Carbon, Nitrogen And Phosphorus Stoichiometry Across Plant Species On The Western Slopes Of Helan Mountain

In recent years, with the global climate changing, the geographic variation in the plant stoichiometry has been of the center in studies about the structure and function of ecosystems. So this resarch explored the characteristics of foliar stoichiometry (C, N, P) and the relations between foliar stoichiometry (C, N, P) with plant phylogeny type, function group and environmental factors across 13 different plant communities with changes of the elevations in Helan mountain, and also studyed the charecteristics of foliar stoichiometry (C, N, P) with changes in soil water availability, leaf size and phonological stage, respectively. The results of this study are shown as follows:1) The contents of folia C, N and P were ordered as:C (413.56 mg g-1)> N (20.58 mg g-1)> P (20.58 mg g-1), and the variances of folia C, N and P contents were ordered as:P (32.98%)> N (27.60%)> C (10.10%). The values of foliar stoichiometry were ordered as:C:P (403.78)> C:N (21.91)>N:P (19.31), and the variances of all these foliar stoichiometry were c.30%. The values of foliar stoichiometry were mainly regulated by the N and P contents,especially the P contents. It showed significant correlation betwenn foliar C、N and P contents, which demonstrate convergent evolution in plant function despite the enormous diversity of plant species and habitats.2) The hillside of Helan mountain was divided into two regions:high-attitude region and low-attitude region, with the mountain steppe (2100 m) as the borderline. In the low-attitude region, the vegetation converted from steppe to desert with the decrease of attitude. The foliar P content increased, while the C:N mass ratio and the C:P mass ratio dicreased gradually. The C:N and the C:P mass ratio did not correlate to the attitude. In the high-attitude region, the vegetation converted from forest to medow gradually with the increase of attitude. Along the gradient, the foliar N, P contents and the N:P mass ratio increased, the C:N mass ratio decreased gradually. The C content and C:P mass ratio did not significantly correlate to the attitude. The results indicate that in the arid and cold region, plants favore acquisition of more mineral elements.The results in the high-attitude region were in agreement with the conclusion that foliar N, P contents increase with the decrease in the annual mean temperature, based on the studies of plant stoichiometry with changes of the latitude. However, there were no significant relationships between foliar C, N, P contents and their mass ratios with the altitude at the scale of the whole mountaion, which may attribute to the different limiting factors for the plant growth in the high-and low-attitude regions.3) There were significant differences in foliar stoichiometry (C, N, P) among plant founction groups, and the correlation of foliar stoichiometry (C, N, P) of each function group with the altitude was different with each other. Additionally, there were no obviouse correlation between foliar stoichiometry (N, P) with soil nutrtion. All these results reflect that the foliar stoichiometry in the large-scale is directly regulated by the type of plant founction group, and the environment index are just indirect factors, that is to say, differences in the cobination of plant founction groups would resulted in the changes in the foliar stoichiometry.4) No consistent tendence about the dynimics of foliar stoichiometry (C, N, P) were found in six shrubs with the changes in grown season.. It showed that enven though the paints were belong to the same function group, there foliar stoichiometry (C, N, P) were also different.5) Foliar stoichiometry (C, N, P) were significantly different with the changes in leaf size. The order of foliar stoichiometry value in plant Zygophyllum xanthoxylum were:P (22.6%)>N (15.21%)>N:P (14.67%)> C:P (13.30%)>C (12.18%) > C:N (8.81%). It showed nagative relationship between foilar C, N and P contents with individual leaf area, and positive relationship between foilar stoichiometry (C, N, P) with individual leaf area.6) Leaves grew slowly and favored acquisition of P over C and N under both high and low water supply. Thus, leaf C:P and N:P ratios were unimodally related to soil water content, in parallel with individual leaf area and mass. As a result, there were significant positive correlations between leaf C:P and N:P with leaf growth. Our results indicated that plant growth and stoichiometry were strongly affected by soil water in this desert shrub.7) No obvious correlation between plant community species richness with foliar stoichiometry (C, N, P) were found in Helan mountain, which did not surpport the view that value of species richness is higher when the foliar N:P mass ratio in 14-16 than that under foliar N:P mass smaller than 14 or bigger than 16. And the hypothesis that there is positive correlation between species richness with the variance of foliar mass ratio was not surpported. It may due to the small changes of plant species richness in our research (9-16 plant species).