沿海拔梯度变化的哀牢山亚热带森林群落系统发育结构

为揭示森林群落系统发育结构在海拔梯度上的变化及其驱动因素, 本研究以云南哀牢山西坡的亚热带森林群落为研究对象, 以APG III系统为基础框架, 结合DNA条形码序列信息解决末端分类单元亲缘关系的方法, 构建了哀牢山森林群落系统发育进化树, 采用净亲缘指数(net relatedness index, NRI)和最近亲缘指数(nearest taxon index, NTI), 探讨了不同植被类型的森林群落系统发育结构和沿海拔梯度的变化规律。结果表明, 从整体的海拔变化趋势上来看, 哀牢山森林群落系统发育结构随海拔上升由系统发育聚集(phylogenetic clustering)走向发散(phylogenetic overdispersion)或聚集程度降低。在低海拔地区, 群落表现为系统发育聚集, 表明生态位理论中的生境过滤作用在群落构建和生物多样性的维持中起着主导作用; 在中海拔地区, 出现了聚集与发散两种群落系统发育结构并存的现象, 推测可能是生境过滤和竞争排斥两种生态过程共同作用的结果; 在高海拔地区, 群落的系统发育结构因选择的指数不同而出现相反的结果, NRI表现出系统发育聚集, 而NTI却表现为随机或发散, 考虑到高海拔地区的环境胁迫可能促使植物发生趋同进化, 推测其群落构建的生态学过程需要更为综合的研究。本研究揭示群落系统发育结构沿海拔梯度确实存在显著的变化, 证明在生态群落的构建过程中非随机过程起到促进乃至关键作用。

Phylogenetic community structure of subtropical forests along elevational gradients in Ailao Mountains of southwest China

Understanding the maintenance of biodiversity and community assembly is a central issue in community ecology. Here, we examined patterns of the community phylogenetic structure of subtropical forests along an elevational gradient in the Ailao Mountains of southwest China. We surveyed all trees with diameter at breast height ≥1 cm in 16 plots, and constructed a community phylogeny from DNA barcode sequence data with a constraint tree based on Angiosperm Phylogeny Group (APG) III. We found that the community structure changed from phylogenetically clustered to phylogenetically overdispersed with increasing elevation. Co-occurring trees at low-elevation communities tended to be more closely related than expected by chance, implying that these communities were structured primarily by habitat filtering. Clustered and over-dispersed phylogenetic compositions were showed in mid-elevation communities, suggesting that these communities are structured by habitat filtering or competitive exclusion. At high-elevation sites, NRI (Net Relatedness Index) showed clustering, but NTI (Nearest Taxon Index) showed randomness or over-dispersion. We therefore interpreted our results with caution. It is possible that convergent evolution may be occurred independently in distantly related lineages under higher environmental stress at high elevations. Taken together, the results of our study provide insight into the potential role of elevational gradients in shaping community composition and phylogenetic diversity.