Stoichiometry Of Pinus Yunnanensis Natural Secondary Forest

Pinus yunnanensis forest is the unique forest type in southwest China, which distributes widely in Yunnan Province. The mostly existing Pinus yunnanensis natural forest is Pinus yunnanensis natural secondary forest forming on the original place due to excessive logging and other unreasonable utilization ways. Based on the fundamental principle and theory of ecological stoichiometry. Pinus yunnanensis natural secondary forest is our research object and Pinus yunnanensis natural old-growth forest for comparison. Field investigation and sampling were conducted in totally 122 plots(4.88hm2). In our study, structure characteristics of Pinus yunnanensis natural secondary forest were studied, and analyzed the ecological stoichiometry characteristics and distribution rule of leaf C, N, P content and their stoichiometric ratios, and we explore the correlation between species diversity and characteristics in community, environmental factors(elevation, slope gradient, slope direction, slope position, soil nutrient), niche characteristics of main species and leaf C, N, P content and their stoichiometric ratios. These studies would provide theoretical support and science reference for vegetation management and protection of Pinus yunnanensis forest. The main results are as follows:1. Based on the invesitigation of Pinus yunnanensis natural secondary forest community and taking the Pinus yunnanensis natural old-growth forest for control, we analyzed the numerical characteristics of community structures and species diversity on different diameter class and different height. The results showed that average diameter and average height of Pinus yunnanensis natural secondary forest stand factor were significantly greater than Pinus yunnanensis natural old-growth forest, but the basal areas and stand density of Pinus yunnanensis natural secondary forest were significantly less than Pinus yunnanensis natural old-growth forest. The species abundance curve reflected the structure of Pinus yunnanensis natural secondary forest was relatively single. Species richness showed an inverse J-shape with diameter class and height increasing in all regions of Pinus yunnanensis natural secondary forest except Southwest Yunnan, and species abundance showed left partial peak curve with diameter class and height increasing. While species richness and abundance of Pinus yunnanensis natural old-growth forest showed an inverse J-shape with diameter class and height increasing. Generally, species diversity of Pinus yunnanensis natural secondary forest was less than the Pinus yunnanensis natural old-growth forest.2. Understanding the changes in the stoichiometric characteristics of forests are key to study nutrient cycling characteristics, limited factors and stability mechanisms of a ecosystem. We selected three stand sites(Southeast Yunnan, Southwest Yunnan, Central Yunnan, China, respectively) in the concentration zone of Pinus yunnanensis natural secondary forests, and Pinus yunnanensis natural old-growth forest(Northwest Yunnan) for control, based on accessibility and elevation distribution. Here we analyzed the leaf C, N, P and stoichiometric ratio of 48 woody species from 94 plots(20m×20m in size)in Pinus yunnanensis natural secondary forests, and 28 plots(20m×20m in size) in Pinus yunnanensis natural old-growth forest. The results showed that the arithmetic mean values of leaf C, N, P and C:N, C:P, N:P ratio for Pinus yunnanensis natural secondary forest were 450.30, 11.16, 1.13mg/g and 45.09, 496.55, 11.32, respectively. Their Coefficient of Variation(CV) were 5.61%, 39.70%, 53.98%, 30.72%, 45.49% and 45.05%, respectively. Leaf C and N, P relationships were showed a significant negative correlation(P<0.01), there was a significant positive correlation between leaf N and P(P<0.01). For different life forms, there were significant differences in leaf N and C:N ratio between tree and shrub(P<0.05), there were significant differences in leaf C, N, P and C:N, C:P ratio between evergreen and deciduous except N:P ratio(P<0.05). There were significant differences in leaf C, N, P and C:N, C:P, N:P ratio between conifer and broadleaf(P<0.05). For leaf C:P and N:P, only one group showed significant differences, leaf C:P between evergreen and deciduous, leaf N:P between conifer and broadleaf(P<0.05). In the Pinus yunnanensis natural secondary forest, the leaves of Pinus yunnanensis compared with other species had higher C content, and lower N, P content, indicated that Pinus yunnanensis had high C assimilative capacity. The correlation between individual abundance and leaf C and C:N, C:P ratio was very significantly positive(P < 0.01), the correlation between individual abundance and leaf N was very significantly negative(P<0.01), the correlation between individual abundance and leaf P was significantly negative(P<0.05), but there was no significant correlation between individual abundance and leaf N:P. The relative low N:P ratioof overall species of Pinus yunnanensis natural secondary forest implies that N element is a limit factor in Pinus yunnanensis natural secondary forests distribution.3. Niche is one of the important theories in the research of modern ecology, it plays an important role on understanding the function of community structure, the interspecific association of species in community, biodiversity, community dynanmic succession and the species evolutionary. Based on the investigation of 94 Pinus yunnanensis natural secondary forest plots, the niche characteristics of top 20 dominant species Pinus yunnanensis natural secondary forest community with the basis of important value and the correlation between leaf C, N, P and their stoichiometric ratio and niche breadth, important value were analyzed by means of Shannow-wiener niche breadth index, Schoener niche similarity index and Pianka niche overlap index. The results showed that the total breadth of niche of Pinus yunnanensis, Schima noronhae, Craibiodendron stellatum, Quercus variabilis, Vaccinium vitis-idaea, Keteleeria evelyniana, Wendlandia uvariifolia were higher and they occupied the dominant position in Pinus yunnanensis natural secondary forest community, had the strong ability of resource utilization. It showed significantly positive correlation between important value and niche breadth which explained that the greater important value, the greater the niche breadth. The niche similarity among the species with great niche breadth was larger, such as 0.7222 between Craibiodendron stellatum and Vaccinium vitis-idaea, 0.5870 between Schima noronhae and Craibiodendron stellatum, 0.5000 between Craibiodendron stellatum and Quercus variabilis. There were 23 species pairs of niche overlaps were 0, and 167 species pairs overlapped less than 0.1. The smaller niche overlap, the higher the niche differentiation which reflected the weaker competition between species in Pinus yunnanensis natural secondary forest community. That means various populations can make full use of resources, the relationship between the populations are harmonious, the Pinus yunnanensis natural secondary forest community is in a relatively stable state. Relevant analysis results between leaf C, N, P and their stoichiometric ratio and important value, niche breadth showed that even in a limited number of N, P nutrient condition, the species with greater important value and niche breadth also had higher nutrient use efficiency.4. Generally, environmental factors affect the growth of plants. In this study, plant leaves and soil sampling were collected and enviromental factors were investigated in Pinus yunnanensis natural secondary forest to study the variation characteristics of leaf C, N, P and their stoichiometry ratios of Pinus yunnanensis natural secondary forest under different environmental factors. The results showed that the leaf stioichiometric characteristics of Pinus yunnanensis natural secondary forest plants was mostly no significant difference along elevation gradient, but the results of Pearson’s correlation analysis showed that there were significant correlation between elevation and leaf C, N:P, along with the rising elevation gradient, leaf C and N:P would decline.. There was a significant difference between 10~20° and 20~30°slope gradient, but there was no significant correlation between leaf C, N, P and stoichiometric ratios of Pinus yunnanensis natural secondary forest plants and slope gradient. The leaf stioichiometric characteristics of Pinus yunnanensis natural secondary forest plants was no significant difference between sunny and shade slope. the relationship among slope aspect and leaf P, N:P was significant positive correlation and significant negative correlation, respectively. On the slope position, the difference of leaf stioichiometric characteristics was significant. Leaf C and N contents were highest in the upper slope, lowest in the down slope; Leaf P content was highest in the middle slope, lowest in the down slope; Leaf C:N was highest in the upper slope, lowest in the down slope; Leaf C:P and N:P were highest in the down slope, lowest in the middle slope.. TThe relationship between slope position and leaf C, N, N:P was very significant negative correlation, significant positive correlation and very significant negative correlation, respectively. For the relationship between soil nutrient and the leaf stioichiometric characteristics of Pinus yunnanensis natural secondary forest plants, the relationship among soil C and leaf C, N, C:N was very significant negative correlation, significant negative correlation, significant positive correlation, respectively. There was a significant negative correlation between soil N and leaf C. But there was no significant correlation between soil P and the leaf stioichiometric characteristics of Pinus yunnanensis natural secondary forest plants.