Plant And Soil Ecologgical Stoichiometry Of Sibiraea Angustata Shrub On The East Of Qinghai-tibetan Plateau

The Qinghai-Tibetan Plateau is the highest plateau on the earth, known as “the roof of the world” and “the third pole of the earth”. Shrub is an extremely important vegetation in China and has a wide distribution area on Qinghai-Tibetan Plateau. Sibiraea angustata is a kind of typical and representative shrub species of alpine shrub on the Qinghai-Tibetan. The sixteen Sibiraea angustata shrub ecosystem plots were selected by the stratified sampling method on the eastern Qinghai-Tibetan Plateau. The plant and soil samples were collected and measured from different parts of ecological systems, and the concentrations of carbon(C), nitrogen(N) and phosphorus(P) and their ecological stoichimetric characteristics were analyzed. Through the study on plant and soil ecologgical stoichiometry of Sibiraea angustata shrub on the east of Qinghai-Tibetan Plateau, the main findings were as follows:The average concentrations of C, N and P in topsoil(0-10 cm) of the sixteen shrub sample plots were 73.27±20.25 g.kg, 6.27±1.8 g.kg and 1.13±0.25 g.kg, respectively. These concentrations were shown to decrease with the increase of soil depth and all showed “inverted Pyramid” types, with different degree of reduction. The coefficients of variation of C, N increased with the increase of soil depth, but that of P was relatively stable. Correlation analysis showed a better correlation between C-N than between C-P and N-P. The average ratios of C:N, C:P and N:P in topsoil(0-10 cm) were 10.47±2.56, 38.66±21.66 and 3.67±1.88, respectively, and the ratio of C:N was relatively stable in all soil layers, but the ratios of C:P and N:P decreased with the increase of soil depth. The coefficients of variation of C:N, C:P and N:P also increased with the increase of soil depth. The results indicated that the distribution characteristics of C:N, C:P and N:P are partly determined by the distribution characteristics of C, N and P.The ranges of C, N and P concentrations of upper part of the herb layer were 247.72-433.32 g.kg-1,12.98-30.31 g.kg-1,1.06-2.88 g.kg-1, the mean values were 364.48 g.kg-1, 16.74 g.kg-1,1.78 g.kg-1 and the coefficients of variation were 15.94%, 26.04%, 30.47%, respectively. However, The anges of C, N and P concentrations of undergroud part of the herb layer were 153.03-419.55 g.kg-1,3.30-14.93 g.kg-1,10.64-2.44 g.kg-1, the mean values were 282.46 g.kg-1, 9.96 g.kg-1,1.25 g.kg-1 and the coefficients of variation were 32.27%, 28.04%, 37.12%, respectively. The concentrations of C, N and P in the upper part of herb layer were more than that on the underground part, but the variation coefficients in the upper were less than that on the ground. The mean values of C:N, N:P and C:P of upper part of the herb layer were 22.52, 9.96, 226.91, and the coefficients of variation were 20.91%, 27.31%, 39.21%, respectively. Nevertheless, The mean values of C:N, N:P and C:P of undergound part of the herb layer were 30.22, 8.83, 271.17, and the coefficients of variation were 38.25%, 32.39%, 57.63%, respectively. The average values of C:N and C:P in the upper part of the herb were less than that of the underground part, while N:P in the upper part of the ground was more than that of the underground part. At the same time, the coefficients of variation of C:N, N:P and C:P in the underground part were more than that of the upper part.The C concentration of Sibiraea angustata shrub was relatively high and stable, with the highest value found in shoot and the lowest value found in leaf, and followed the order of: shoot(495.07 g.kg-1) > twig(483.37 g.kg-1) > fruit(480.35 g.kg-1) > root(468.47 g.kg-1) > leaf(466.33 g.kg-1). Meanwhile, the mean concentrations of N, P of different organs occurred in descend order as follows: leaf(22.27 g.kg-1) > fruit(19.74 g.kg-1) > twig(7.98 g.kg-1) > shoot(4.54 g.kg-1) > root(4.00 g.kg-1) and fruit(2.85 g.kg-1) > leaf(1.92 g.kg-1) > twig(0.96 g.kg-1) > root(0.52 g.kg-1) > shoot(0.45 g.kg-1), respectively. The ranges of values of coefficient of variation(CV) for C, N and P concentrations were 1.71%-4.44%, 14.49%-25.50% and 11.46%-46.15%, respectively. Specifically, the highest CV values for N and P were found in roots. The mean concentrations of leaf N and P were 22.27 g.kg-1 and 1.92 g.kg-1, respectively. Correlation analysis indicated that the C concentration was significantly negatively correlated with N and P concentrations, whereas N concentration had dramatically positive correlation with P concentration. Based on variation analysis among different organs, the C:N and C:P values of leaf and fruit were apparently lower than root, swig and shoot. In addition, the N:P value of different organs varied from 7.12-12.41 and the lowest value was found in fruit. These results could indicate that the C, N and P stoichiometric characteristics in the Sibiraea angustata shrub accorded with the homeostatic mechanism and growth rate hypothesis to some extent, the distributions of C, N and P were closely related to the function of the organs.Correlation analysis indicated that the C concentration of Sibiraea angustata shrub was significantly negatively correlated with N and P concentrations, whereas the C concentration of herb was significantly positively correlated with N concentration but had dramatically negative correlation with P concentration, which could indicate there might be some differences in the mechanism of C, N and P co-utilization of shrub and herb. Because there are leaves with high C, N and P concentrations and fertile soil in Sibiraea angustata shrub, there was a certain difference in judging the nutrient limitation of the species by using the N:P index of soil or shrub leaves and it should be prudent to use ecological stoichiometric ratios to judge the limiting condition of nutrient at the species level or fertile soil. With respect to herb, shrub on C uptake and storage capacity was higher.