The Nitrogen And Phosphorus Stoichiometrical Mechanism Of Phyllostachys Edulis Expansion Effect On Forests Plant Diversity

Phyllostachys edulis expansion had large effects on the adjacent forest ecosystems species diversity, but the related effect mechanism is still unclear. The ecological stoichiometry is a science that utilizes the basic principles in biology, chemistry and physics to study the balance of elements in biosystem. So this study used space-time substitution method, comparatively analyzed the species diversity, leaves N and P content, N:P of tree, shrub and herb, also in the forest soil between different communities that include the Ph. edulis forest(PEF), Ph. edulis-tree mixed forest and the adjacent evergreen broad-leaved forests(EBF) or Cunninghamia lanceolata plantation(CLP) in Jinggangshan national nature reserve, Jiangxi Province. Try to explain the cause of species diversity were effected by Ph. edulis expansion from the perspective of ecological stoichiometrical internal balance. The results are as followed:(1) The effects of Ph. edulis expansion on various levels species diversity in adjacent broad-leaved forest were different. The species diversity of tree layer were significantly reduced, the Shannon-Wiener index declined from 2.56 to 0.06, drop as much as 98 %; the species diversity of shrub layer were also decreased, Shannon-Wiener index was from 2.58 to 2.58, a drop of about 22 %; but the species diversity of herb layer were increased, Shannon-Wiener index rose from 2.64 to 2.95, rising by about 12 %.(2) Ph. edulis expansion has affected the evergreen broad-leaved forest community structure. It decreased the layers of the evergreen broad-leaved forest community lead to a single vertical structure, the abundance percentage from 12 to 14 m accounted for 33.3 %; At the same time it also reduced the level of individual large diameter lead to diameter level mainly distributed in 5 to 10 cm, and the abundance percentage is as high as 90.0 %. So the evergreen broad-leaved forest community structure showed single by Ph. edulis expansion.(3) The nitrogen and phosphorus stoichiometrical characteristics were different for tree layer species. The balance adjustment ability was strongest for Ph. edulis and its leaves N:P changed a little and remained 16.0 during the expansion process; then the balance adjustment ability was strong and the mature leaves N:P was 13.0 for Cunninghamia lanceolata, but its yong leaves and litter N:P declined about 18 % on average; however the balance adjustment ability was lowest and the range of leaf N:P was 20.0-23.0 for broad-leaf trees, its leaves N:P delined about 20.0-30.0 % by Ph. edulis expansion.(4) The nitrogen and phosphorus stoichiometrical characteristics were also different for shrub layer species. The internal balance adjustment ability was relatively strong for Camellia oleifera, Ardisia crenata and Eurya muricata while that was common for Lindera erythrocarpa and Machilus thunbergii. Leaf N:P dropped about 20.0 % by Ph. edulis expansion for Lindera erythrocarpa.(5) However, the nitrogen and phosphorus stoichiometrical characteristics were no significant different for herb layer species. Leaf N:P plasticity were stronger and maintained at 16.0-20.0, dropped less than 10.0 % by Ph. edulis expansion.(6) The adjacent forest ecological system significantly increased soil P content, soil N:P decreased significantly by Ph.edulis expansion. The soil N:P was 6.0 for PEF sample plots, that was 9.0 for EBF sample plots and was 10.0 for CLP sample plots, a drop of about 35-40.0 %.(7) The response of different levels plant to soil nutrient change were different. Leaves N:P and soil N:P was significantly positively related for tree layer species; that was no significant correlation for shrub layer species and was significant negative correlation for herb layer species.In a word, Ph. edulis expansion lead to the soil P content increase and soil N:P decrease significantly for secondary evergreen broad-leaved forest and Cunninghamia lanceolata plantation in Jinggang nature reserve, Jiangxi Province. And that caused different degree influences on the leaf nitrogen and phosphorus stoichiometrical characteristics for the three levels species, including trees were most affected, shrubs were affected moderately, herbaceous were affected lightest. We speculated that adjacent forest soil nutrient changed by Ph. edulis expansion, resulting in element stoichiometric imbalance in the plant, may be the important cause of the change of the plant diversity. The findings for discussing effect mechanism of biological invasion on the biodiversity provide a new angle of view, also provide theoretical reference for biodiversity protection.