ABSTRACT
Pure and mixed larch (Larix pricipis-rupprechtii) and birch (Betula platyphylla) plantations in Saihanba area were selected as test objects, with two stand density (200-340 and 880-1100 trees·hm-2) of each stand type. Based on tree size-stratified sampling approach, a total of 668 tree core samples were collected. A linear mixed model was used to analyze the effects of tree species interaction, stand density, and tree size on larch productivity. Results showed that basal area increment of larch was affected by competition, diameter at breast height, tree age, and neighborhood density to different degrees. Overyielding of larch was mainly due to the positive effect of birch on larch growth in the mixed plantation with higher stand density. For mixed plantation with lower stand density, the productivity of those two species was lower than that pure plantation because of a lack of species interaction. Intraspecific competition was the main factor influencing larch productivity. Larch productivity was positively affected by tree size, with the magnitude of tree size effect varying with stand density and species composition. Suitable enhancement of stand density and selection of birch as the mixing tree species could improve productivity of larch.
Subject(s)
Larix , Betula , TreesABSTRACT
Litter is an important contribution to forest soil. Litter decomposition plays an important role in nutrient cycling of forest ecosystem. A field litterbag experiment was conducted to examine the dynamics of decomposition rate, nutrient release and enzyme activity during litter decomposition in the pure forests of Larix principis-rupprechtii (L) and mixed forests, including L and Betula platyphylla (B), L and Quercus mongolica (Q), as well as LBQ, in Saihanba area, Hebei Pro-vince, China. The results showed that the decomposition rate of leaf litter in L forest was significantly lower than that in mixed forests during the 720 d decomposition. The LB had the highest decomposition rate of L leaf litter. All treatments had the same change trend of nutrient contents, with the contents of N and P being increased and that of C, K and C/N being decreased. Contrast to pure leaf litter of L, leaf litter in mixed forests could promote the release of C and K, and inhibit litter N and P release. During the litter decomposition, the activities of catalase, urease and acid phosphatase increased, while that of sucrase decreased in all leaf litter of forests. The decomposition rate of leaf litter was positively correlated with the activities of catalase, urease and acid phosphatase, negatively correlated with that of sucrase. Our results showed that leaf litter mixture of L. principis-rupprechtii, B. platyphylla and Q. mongolica could enhance the litter decomposition of L. principis-rupprechtii, and that enzyme activities were closely related to litter decomposition.
Subject(s)
Larix , Trees , China , Ecosystem , Forests , Nutrients , Plant Leaves , SoilABSTRACT
Biodegradable polymeric nanoparticles, which hold hierarchical morphologies, are of importance for controlled drug delivery. In this work, nanoparticles with fennel-like morphology were prepared from graft copolymers of hydroxyethylcellulose and poly(p-dioxane). The effect of microstructure parameters on the morphological transition of the nano-aggregates was studied and the nanoparticles were investigated as a carrier of hydrophobic drug. The morphology and drug release property of the nanoparticles were found to be related with the degree of substitution and molecular weight of graft chain of the copolymer.
