[Seedling regeneration and spatial correlation between seedlings and seed trees in Castanopsis hystrix plantation by large diameter wood cultivation in south subtropical China]. / å—äºšçƒ­å¸¦çº¢é”¥å¤§å¾„æåŸ¹è‚²æž—å¹¼è‹—æ›´æ–°åŠå ¶ä¸Žæ¯æ ‘çš„ç©ºé—´å ³è”æ€§.

Using the paired correlation equation g(r) in the spatial point patterns, we investigated the regeneration characteristics and spatial patterns of Castanopsis hystrix seedlings and the spatial correlation with the seed trees in the plantation by large diameter wood cultivation in south subtropical China. The results showed that natural seedling regeneration in C. hystrix plantation was good, which were widely distributed in the whole plantation. The seedling regeneration were mainly contributed by root sprouts, accounting for 73.6% of the total. The number distribution of C. hystrix seedlings in different age classes showed a pyramidal shape, with the contribution of diameter class1, 2 and 3 being 64.3%, 29.3% and 6.4% of the total, respectively. The C. hystrix seedlings mainly presented aggregated distribution in small scale (<15 m). With the increases of size classes and spatial scales, the aggregation strength gradually weakened and finally presented random distribution. The spatial correlation between seedlings and seed trees was not significant with the increases of size classes or spatial scale.

Differential effects of conifer and broadleaf litter inputs on soil organic carbon chemical composition through altered soil microbial community composition.

A strategic selection of tree species will shift the type and quality of litter input, and subsequently magnitude and composition of the soil organic carbon (SOC) through soil microbial community. We conducted a manipulative experiment in randomized block design with leaf litter inputs of four native subtropical tree species in a Pinus massoniana plantation in southern China and found that the chemical composition of SOC did not differ significantly among treatments until after 28 months of the experiment. Contrasting leaf litter inputs had significant impacts on the amounts of total microbial, Gram-positive bacterial, and actinomycic PLFAs, but not on the amounts of total bacterial, Gram-negative bacterial, and fungal PLFAs. There were significant differences in alkyl/O-alkyl C in soils among the leaf litter input treatments, but no apparent differences in the proportions of chemical compositions (alkyl, O-alkyl, aromatic, and carbonyl C) in SOC. Soil alkyl/O-alkyl C was significantly related to the amounts of total microbial, and Gram-positive bacterial PLFAs, but not to the chemical compositions of leaf litter. Our findings suggest that changes in forest leaf litter inputs could result in changes in chemical stability of SOC through the altered microbial community composition.

[Characteristics of carbon storage and its allocation in Erythrophleum fordii plantations with different ages].

Carbon storage and its allocation of 7-, 29- and 32-year-old Erythrophleum fordii plantation ecosystems in Guangxi were studied on the basis of biomass survey. The results showed that the carbon contents in different organs of E. fordii, ranging from 509.0 to 572.4 g x kg(-1), were in the order of stem > branch > root > bark > leaf. No significant differences in carbon content were observed among the shrub, herb and litter layers of the E. fordii plantations with different ages. Carbon content in the soil layer (0-100 cm) decreased with increasing the soil depth, but increased with increasing the stand age. The carbon storage of the arbor layer was 21.8, 100.0 and 121.6 t x hm(-2) for 7-, 29- and 32-year-old stands, respectively, and the order of carbon storage allocation in different organs was same as the order of carbon content. The 7-, 29- and 32-year-old E. fordii plantation ecosystems stored carbon at 132.6, 220.2 and 242.6 t x hm(-2), respectively. The arbor layer and soil layer were the main carbon pools, accounting for more than 97% of carbon storage in the ecosystem. Carbon storage allocation increased in arbor layer but decreased in soil layer with increasing the stand age. The influence of stand age on carbon storage allocation in shrub, herb and litter layers did not show a obvious regular pattern.

[Soil physical and chemical characteristics under different vegetation restoration patterns in China south subtropical area].

This paper studied the change of soil physical and chemical properties under eleven vegetation restoration patterns (1 kind of secondary forest, 2 kinds of pure coniferous plantations, 5 kinds of evergreen broad-leaved plantations, 2 kinds of conifer and broad-leaved mixed plantations, and 1 kind of shrub) typical in Daqingshan of Guangxi. Obvious differences were observed in the soil physical and chemical properties under different vegetation restoration patterns. The soil physical properties were better in secondary forest but poorer in pure conifer plantations. Conifer and broad-leaved mixed plantations had lower soil bulk density, and their soil total porosity and water-holding capacity were higher than those in pure plantations. There were no significant differences in the soil porosity among the 5 evergreen broad-leaved plantations. Except that of soil total K, the contents of soil nutrients in secondary forest were higher than those in plantations, and the soil C/N ratio and pH value were relatively lower. Comparing with shrub, the 9 plantations had an obvious change in their soil nutrient contents, e. g. , the increase of soil total N and available K. The 2 pure coniferous plantations had lower soil nutrient contents, but after mixed planted with evergreen broad-leaved trees, their soil nutrient contents increased markedly, and the soil C/N ratio decreased.

[Effects of Pinus massoniana plantation stand density on understory vegetation and soil properties].

By using plot investigation and sampling analysis methods, the understory vegetation and soil properties of Pinus massoniana plantations with different stand density in subtropical area were studied in Daqingshan, Guangxi Province. In the P. massoniana plantations after 14-year natural growth, the understory species diversity index of shrub layer increased with the increase of stand density from 1050 trees x hm(-2) to 1800 trees x hm(-2), but decreased when the stand density further increased to 2250 trees x hm(-2). Herb species diversity index was not sensitive to the stand density change. With increasing stand density, shrub biomass had the same variation trend as that of shrub species diversity index, while herb biomass decreased with increasing stand density. Significant differences (P < 0.05) were observed in the soil (0-20 cm) physical and chemical properties between the plantations with different stand density. The soil nutrient contents except those of total P and available K and P had the same variation trend with that of the understory species diversity index of shrub layer. Soil available K and P contents fluctuated with stand density, whereas soil total P content was higher when the stand density was 2100 trees x hm(-2). In the plantations with moderate stand density (1800 trees x hm(-2)) , soil water-holding capacity and soil porosity were higher, and soil bulk density was lower.