Leaf N,P Stoichiometry And Allocation Of Main Deciduous And Evergreen Tree Species In Tiantong National Forest Park, Zhejiang Province, China

In the subtropical region, the evergreen broad-leaved and deciduous broad-leaved tree species usuualy coexisted in the evergreen broad-leaved forests, however, the inner mechanism has not been explaied satisfactorily. This thesis studied N, P stoichiometry and N, P allocation proportion in the cell wall (Ncw/Nm, Pcw/Pm) of the leaves of the tree species with different life forms in the evergreen broad-leaved forest, the seasonal dynamic of N, P charicteri sties of the young and old leaves of the typical evergreen tree species and the deciduous species, as well as those of the soil in the two habitats, leaf traits of evergreen and deciduous tree species and their correlation with the photosynthetic efficiency in the two habitats, from which then the reasons of the coexistence of the deciduous and the evergreen tree species in the evergreen broad-leaved forest were tried to explain. The main conclusions were as follows:(1) The contents of N and P, N:P, Ncw/Nm, and Pcw/Pm of the leaves of the deciduous and the evergreen broad-leaved trees and shrubs showed significant differences. The contents of N and P of the leaves of the deciduous trees were higher but Ncw/Nm, Pcw/Pm were lower than those of the evergreen trees, which indicated that the evergreen tree leaves allocated more N and P to their defense structure. P of the trees leaves positively correlated with N and N:P, but N and N:P were not significantly correlated.(2) The contents of N and P of the leaves of the deciduous trees were significantly lower than those of the evergreen trees. The growth of deciduous tree was mainly limited by N concent, and leaf N:P of evergreen plant was more than16which indicated that the growth of the evergreen broad-leaved tree species was limited by P concent. The N:P in the young leaves of the evergreen broad-leaved trees was significantly lower than that of the old leaves, indicating that the young leaves were more easly limited by N than the old leaves.(3) The N and P stoichiometry seasonal dynamics of the young and old leaves of the evergreen tree species and leaves of the deciduous tree species were significantly different. The seasonal trend of N, P content of the young leaves of the evergreen species increased to the maximum value in spring, but decreased in summer, and then increased gradually in winter; The seasonal trend of Ncw/Nm, Pcw/Pm of it gradually increased as leaf grow up.The N, P content of the old leaves were minimum in the germination period, then recovered gradually over time; Ncw/Nm, Pcw/Pm of the old leaves were minimum in summer, then recovered rapidly in winter. The seasonal trends of the leaf N and P of the deciduous trees were consistent. The leaf N, P decreased gradually over time until the fall. But Ncw/Nm, Pcw/Pm were the opposite.(4) The seasonal dynamics characteristics of the content of N and P and N:P in soil in the two habitats exhibited consistent with thoese of the young leaf of the evergreen tree species, i.e., the content of N, P and N:P in soil were highest in spring and lowest in summer, then began to rebound in autumn and winter, showing "V" type variation, indicating that the N, P of the tree leaves during the growing season were affected by soil N and P. The N and P content and N:P in the upper layer soil were higher than those of the lower layer soil.(5) In different habitats, photosynthetic characteristics and leaf traits of deciduous tree species were significantly different from those of the evergreen tree species. Amass and PUNE of the evergreen trees species were lower but LMA, Ncw/Nm and Pcw/Pm were higher than deciduous tree species. The evergreen tree species tended to use more nitrogen to protect the photosynthetic system and defense system in the open habitat, showed adaptive strategies characterized by persistence and maintaining survival. The deciduous tree species showed lower LMA, Ncw/Nm and Pcw/Pm but higher Amass and PNUE, allocating more nutrition into the photosynthetic organ. At the expense of shorter life-span, the deciduous tree species showed adaptive strategies characterized by high nitrogen-use efficiency in response to the change of the habitat conditions.