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Studying community phylogenetic diversity within forest stands of different diameter classes (i.e. size classes) is helpful for understanding relationships among species at different ages while at the same time community phylogenetic structure. However, little research has been focused on the influence of species abundance on phylogenetic structure of community. This study was conducted in the Jianfengling tropical montane rainforest on Hainan Island. First, we assessed the impact of species abundance on four widely used phylogenetic diversity indices at different size classes. Next, two of the indices (i.e. net relatedness index, •研究报告• 618 生 物 多 样 性 Biodiversity Science 第 24 卷 NRI and nearest taxon index, NTI) were standardized and used to quantify phylogenetic relatedness of woody plants at different size classes across a series of local habitat types. The results showed that: (1) The unweighted MPD (mean pairwise distance) index significantly overestimated phylogenetic diversity relative to MPD weighted according to species abundance. This overestimation when using unweighted MPD was greatest for small trees and shrubs (1 cm≤DBH 0). However, this pattern continued to show overdispersion within communities made up of large trees (DBH≥15 cm) (NTI

Aims Estimating soil organic carbon (SOC) density and influence factors of tropical virgin forests in Hainan Island provide new insight in basic data for SOC pool estimation and its dynamics study. Methods The main distribution areas of tropical virgin forests in Jianfengling (JFL), Bawangling (BWL), Wuzhishan (WZS), Diaoluoshan (DLS), Yinggeling (YGL) of Hainan Island were selected, and soil samples (0–100 cm) were sampled and analyzed. SOC density was estimated by soil vertical fitting method and soil stratification method to discover the distribution characteristics of soil organic carbon in tropical virgin forests of Hainan Island. Important findings Results showed that: (1) The average SOC density using soil vertical fitting method in JFL, BWL, WZS, DLS and YGL was 14.98, 18.46, 16.48, 18.81, 16.66 kg·m, respectively, which was significantly higher (p < 0.05) than the estimated average SOC density using soil stratification method in these areas (14.73, 16.24, 15.50, 16.91, 15.03 kg·m, respectively). It is better to use soil vertical fitting method for SOC density estimation when the soil was natural without disturbance. (2) The proportion of SOC content in the first 0–30 cm depth interval out of SOC in the whole 0–100 cm soil profiles in JFL, BWL, WZS, DLS and YGL was 50.50%, ©植物生态学报 Chinese Journal of Plant Ecology 杨怀等: 海南岛热带原始森林主要分布区土壤有机碳密度及影响因素 293 doi: 10.17521/cjpe.2015.0314 48.56%, 43.49%, 47.37%, 42.88%, respectively. (3) SOC density was significantly negative correlated with Shannon-Wiener index, Simpson index, species richness, and soil bulk density; and was significantly positive correlated with altitude, soil porosity, and soil nitrogen. However, SOC density was not significantly correlated to slope, biomass, average diameter at breast height, or average height. (4) Our study area Hainan was located in low latitude area with high rainfall and high temperature, which accelerated the decomposition of organic matter and nutrient recycling, resulting in significantly lower SOC densities in this tropical virgin forests of Hainan Island than the average value in China.

The growth performance of individual plants in a population can be affected by the plant-plant interaction, which has been well recognized and is called neighborhood interference. Though mechanisms are still unclear, the variations in gas exchange parameters in relation to the neighborhood interference between individual plants are crucial for evaluating the effects of plant-plant interaction. CO 2 assimilation in leaves of teak under natural conditions of dry seasons and wet seasons as well as its response to variations in light flux density and CO 2 concentration in different neighborhood interferences were simultaneously measured with Li-6400 portable photosynthesis system in a 21-year-old tropical plantation forest in Jianfengling, Hainan Island, China. This article dealt with the change rule of neighborhood interference on tree characteristics of gas exchange and its dynamic response to light en-vironments of individual plants. Diurnal courses of photosynthesis of individual leaves were not affected by neighborhood interfer-ence, but net photosynthetic rates showed a negative relationship with the intensity of neighborhood interference. The ratio of daily average P n in weak, moderate, strong and heavy neighborhood interferences was 2.5:2.3:1.7:1.0, and the daily maximum P n in weak interference was 2.8 times that in heavy interference. Leaf transpiration and stomatal conductance decreased with the increasing of interference intensity. Characteristics of photosynthetic light response and CO 2 response changed with the neighborhood interference, and values of leaf gas exchange parameters including A sat , Q sat , α A , CE , V cmax and J max in weak interference were enhanced by 2.7, 1.3, 1.4, 2.7, 1.9 and 2.8 times, respectively, than those in heavy interference. But changes in those parameters partly depended on light environment and CO 2 concentration, and the influence of changes in light environment on weak interference individuals was sig-nificantly stronger than that on heavy interference. Beyond the growth CO 2 concentration, the influence resulting from changes in CO 2 concentration on heavy interference individuals was obviously stronger than that on weak interference. Neighborhood interference can be described as a major means of intraspecific competition of population in a plantation forest with uniform forest structure and consistent management. Carbon assimilation can be affected by the neighborhood interference, and result in divergence in growth performance. Indices of neighborhood interference can be used to evaluate the intraspecific competition, and based on this point, we can make maximum use of resources after stand structure has been well adjusted.