Data from: Nutrient limitation of woody debris decomposition in a tropical forest: contrasting effects of N and P addition

Tropical forests represent a major terrestrial store of carbon (C), a large proportion of which is contained in the soil and decaying organic matter. Woody debris plays a key role in forest C dynamics because it contains a sizeable proportion of total forest C. Understanding the factors controlling the decomposition of organic matter in general, and woody debris in particular, is hence critical to assessing changes in tropical C storage. We conducted a factorial fertilization experiment in a tropical forest in South China to investigate the influence of nitrogen (N) and phosphorus (P) availability on woody debris decomposition using branch segments (5 cm diameter) of four species (Acacia auriculaeformis, Aphanamixis polystachya, Schefflera octophylla, and Carallia brachiata) in plots fertilized with +N, +P, or +NP, and controls. Fertilization with +P and +NP increased decomposition rates by 5–53%, and the magnitude was species specific. Contrary to expectations, we observed no negative effect of +N addition on decay rates or mass loss of woody debris in any of the four study species. Decomposition rates of woody debris were higher in species with lower C : P ratios regardless of treatment. We observed significant accumulation of P in the woody debris of all species in plots fertilized with +P and +NP during the early stages of decomposition. N release from woody debris of Acacia (N-fixing) was greater in the +P plots towards the end of the study, whereas fertilization with +N had no impact on the patterns of nutrient release during decomposition. Synthesis: Our results indicate that decomposition of woody debris is primarily constrained by P availability in this tropical forest. However, contrary to expectations, +N addition did not exacerbate P limitation. It is conceivable that decay rates of woody debris in tropical forests can be predicted by C : P or lignin : P ratios, but additional work with more tree species is needed to determine whether the patterns we observed are more generally applicable.

热带森林是陆地碳（carbon, C）的主要储存库，其中很大一部分碳储存在土壤与腐解有机质中。木质残体在森林碳动态中发挥关键作用，因其占森林总碳储量的比例可观。因此，阐明调控广义有机质尤其是木质残体腐解的影响因子，对评估热带碳储量变化至关重要。
本研究在中国南方的一处热带森林中开展双因素施肥试验，选取4个树种的直径5 cm枝条切段作为腐解材料，涉及树种包括Acacia auriculaeformis、Aphanamixis polystachya、Schefflera octophylla与Carallia brachiata；试验样地分为施氮（nitrogen, N，+N）组、施磷（phosphorus, P，+P）组、施氮磷复合肥（+NP）组以及对照组，旨在探究氮与磷的有效性对木质残体腐解的影响。
施磷（+P）与施氮磷复合肥（+NP）可使腐解速率提升5%~53%，且提升幅度因树种而异。与预期相悖的是，在四个受试树种中，施氮（+N）均未对木质残体的腐解速率或质量损失产生负面影响。无论施肥处理如何，木质残体的腐解速率在碳磷比（C:P）更低的树种中更高。
在施磷（+P）与施氮磷复合肥（+NP）样地中，所有受试树种的木质残体在腐解早期均出现了显著的磷（P）富集现象。试验后期，固氮金合欢（Acacia auriculaeformis）的木质残体在施磷（+P）样地中的氮（N）释放量更高；而施氮（+N）对腐解过程中的养分释放模式无显著影响。
综合分析：本研究结果表明，该热带森林中木质残体的腐解主要受磷（P）有效性限制。但与预期相悖的是，施氮（+N）并未加剧磷素限制。据此推测，热带森林木质残体的腐解速率可通过碳磷比（C:P）或木质素（lignin）磷比（lignin:P）进行预测，但未来仍需开展包含更多树种的研究，以验证本研究观测到的规律是否具有普适性。