Data from: Determinants of litter decomposition rates in a tropical forest: functional traits, phylogeny and ecological succession

Plant litter decomposition is one of the most important processes in terrestrial ecosystems, as it is a key factor in nutrient cycling. Decomposition rates depend on environmental factors, but also plant traits, as these determine the character of detritus. We measured litter decomposition rate for 57 common tree species displaying a variety of functional traits within four sites in primary and four sites in secondary tropical forest in Madang Province, Papua New Guinea. The phylogenetic relationships between these trees were also estimated using molecular data. The leaves collected from different tree species were dried for two days, placed into detritus bags and exposed to ambient conditions for two months. Nitrogen, carbon and ash content were assessed as quantitative traits and used together with a phylogenetic variance-covariance matrix as predictors of decomposition rate. The analysis of the tree species composition from 96 quadrats located along a successional gradient of swidden agriculture enabled us to determine successional preferences for individual species. Nitrogen content was the only functional trait measured to be significantly positively correlated with decomposition rate. Controlling for plant phylogeny did not influence our conclusions, but including phylogeny demonstrated that the mainly early successional family Euphorbiaceae is characterized by a particularly high decomposition rate. The acquisitive traits (high nitrogen content and low wood density) correlated with rapid decomposition were characteristic for early successional species. Decomposition rate thus decreased from early successional to primary forest species. However, the decomposition of leaves from the same species was significantly faster in primary than in secondary forest stands, very probably because the high humidity of primary forest environments keeps the decomposing material wetter.植物枯落物分解（plant litter decomposition）是陆地生态系统中最重要的过程之一，亦是养分循环（nutrient cycling）的关键驱动环节。分解速率既受环境因子调控，同时与植物功能性状密切相关，而植物性状决定了枯落物的固有特性。本研究针对巴布亚新几内亚马当省的4处原始热带林与4处次生热带林样地，测定了57种涵盖多样功能性状的常见乔木的枯落物分解速率；同时利用分子数据估算了这些乔木的系统发育关系（phylogenetic relationships）。实验过程中，采集自不同乔木物种的叶片经2天烘干处理后被装入枯落物袋，置于原位环境中暴露2个月。研究人员测定了氮、碳与灰分含量作为数量性状，并结合系统发育方差-协方差矩阵（phylogenetic variance-covariance matrix）作为分解速率的预测因子。通过对沿刀耕火种演替梯度分布的96个样方的乔木物种组成进行分析，本研究明确了各物种的演替偏好性。氮含量是唯一与分解速率呈显著正相关的功能性状。控制植物系统发育关系并未改变本研究的结论，但纳入系统发育信息后发现，以早期演替类群为主的大戟科（Euphorbiaceae）具有极高的枯落物分解速率。与快速分解相关的获取型功能性状（高氮含量、低木材密度）是早期演替物种的典型特征，因此分解速率从早期演替物种向原始林物种逐渐降低。然而，同一物种的叶片在原始林样地中的分解速率显著快于次生林样地，这很可能是因为原始林环境的高湿度使分解基质始终保持湿润状态。