Environmental filtering and dispersal limitation jointly shaped the taxonomic and phylogenetic beta diversity of natural forests in southern China.

AIM: The mechanisms underlying the maintenance of biodiversity remain to be elucidated. Taxonomic diversity alone remains an unresolved issue, especially in terms of the mechanisms of species co-existence. We hypothesized that phylogenetic information could help to elucidate the mechanism of community assembly and the services and functions of ecosystems. The aim of this study was to explore the mechanisms driving floral diversity in subtropical forests and evaluate the relative effects of these mechanisms on diversity variation, by combining taxonomic and phylogenetic information. LOCATION: We examined 35 1-ha tree stem-mapped plots across eight national nature reserves in Guangxi Zhuang Autonomous Region, China. TAXON: Trees. METHODS: We quantified the taxonomic and phylogenetic ß-diversity between each pair of plots using the (abundance-based) Rao's quadratic entropy and the (incidence-based) Sørensen dissimilarity indices. Using a null model approach, we compared the observed ß-diversity with the expected diversity at random and calculated the standard effect size of the observed ß-diversity deviation. Furthermore, we used distance-based redundancy analysis (dbRDA) to partition the variations in taxonomic and phylogenetic observed ß-diversity and ß-deviation into four parts to assess the environmental and spatial effects. RESULTS: The taxonomic ß-deviation was related to and higher than the phylogenetic ß-deviation (r = .74). This indicated that the species turnover between pairwise plots was mainly the turnover of closely related species. Higher taxonomic and phylogenetic ß-deviation were mainly concentrated in the pairwise karst and nonkarst forest plots, indicating that the species in karst forests and nonkarst forests were predominantly from distantly related clades. A large proportions of the variation in taxonomic and phylogenetic ß-deviation were explained by the joint effect of environmental and spatial variables, while the contribution of environmental variables was greater than that of spatial variables, probably owing to the influence of the sampling scale dependence, integrality of sampling size and species pool, and the unique climatic and geomorphic characteristics. MAIN CONCLUSIONS: Our study highlights the importance of phylogeny in biodiversity research. The incorporation of taxonomic and phylogenetic information provides a perspective to explore potential underlying mechanisms that have shaped species assemblages and phylogenetic patterns in biodiversity hotspots.

[Foliar stable carbon isotope composition and water use efficiency of plant in the Karst seasonal rain forest.] / å–€æ–¯ç‰¹å­£èŠ‚æ€§é›¨æž—æ¤ç‰©å¶ç‰‡ç¢³åŒä½ç´ ç»„æˆåŠæ°´åˆ†åˆ©ç”¨æ•ˆçŽ‡.

To enrich niche partition and species coexistence theory in karst seasonal rain forest, and provide reference for species selection and configuration for rocky desertification control, we exami-ned foliar stable carbon isotope composition (δ13C) and water use efficiency (WUE) of the representative species in different habitats and the same tree species in different habitats. The results showed that foliar δ13C value in karst seasonal rain forest ranged from -34.13‰ to -29.69‰, with a mean value of (-31.40±1.19)‰. WUE ranged from 9.08-58.76 µmol·mol-1, with a mean value of 41.79 µmol·mol-1. Both of them were lower than subtropical and warm temperate forests at higher latitude, but higher than tropical rain forests at lower latitude and non-karst seasonal rain forests at the same latitude. The foliar δ13C value and WUE of representative species gradually increased with the increases of drought index from the depression to the top of the mountain. The foliar δ13C value and WUE of the same tree species increased with altitude. These results indicated that water use efficiency of tree species was not only related to climate factors, but also related to the geological background and water availability of the habitat. The water use efficiency of plants in karst area was higher than that in non-karst area, and was higher in dry habitat than in wet habitat under the same climatic condition. It showed that having different water use efficiencies was one of the strategies for plants in karst area to adapt to different habitats and maintain species coexistence.

[Spatial patterns of and specific correlations between dominant tree species in a karst evergreen and deciduous broadleaved mixed forest in Mulun Karst National Nature Reserve].

In order to understand the biological characteristics and specific correlations of dominant tree species in a karst characteristic evergreen and deciduous broad-leaved mixed forest in Mulun National Nature Reserve of Guangxi, a point pattern analysis was made on the spatial distribution patterns and inter- and intraspecific correlations of four dominant species in a one-hectare plot. Among the four species, Boniodendron minius dominated in tree sublayer I, while Ligustrum japonicum, Sinosideroxylon wightianum, and Rapanea kwangsiensis dominated in tree sublayers II and III. All the four species had a clumped distribution at scale <10 m, a transition from clumped to random distribution at scale 10-25 m, and a random or regular distribution at scale >25 m. The critical scale from clumped to random distribution varied with species. No significant correlations were observed between the B. minius in sublayer I and the dominant species in sublayer II. The correlations of B. minius with the dominant species in sublayers II and III showed greater fluctuation, with significant positive correlation for L. japonicum at scale <50 m, no significant correlation for S. wightianum, and no significant correlation for R. kwangsiensis at scale <20 m but significant negative correlation at scale 20-50 m.