Humid tropical forests on highly weathered soils are often characterized by low bioavailable phosphorus (P) concentrations. These ecosystems also often experience low and fluctuating redox conditions. Little is known about how soil redox conditions affect P availability and how this might feedback on biogeochemical cycling. Here we used soils from a wet tropical rainfall gradient in Puerto Rico to explore the effects of redox on P bioavailability and associated biogeochemical processes. Concentrations of soil carbon (C) and poorly crystalline iron (Fe) and aluminum (Al) minerals increased at least twofold with increasing rainfall, reflecting stronger anaerobic conditions at wetter sites and associated declines in decomposition. The fraction of the total P pool in the NaOH-extractable organic form also generally increased with increasing rainfall. In a laboratory incubation experiment using three sites along the gradient, P amendment increased aerobic CO₂ production. However, anaerobic processes, including anaerobic respiration, Fe reduction, and methanogenesis, increased with P amendment at the driest site only. Microbial biomass C:P ratios decreased with P amendment under anoxic conditions at the driest site, an indicator of possible microbial P limitation at this site. Both microbial biomass C and P concentrations were lower under anoxic conditions than under oxic conditions across all soils, suggesting that anoxic conditions could be a more limiting factor to microbes than P concentrations. Overall, our results demonstrate that redox conditions regulate the extent of P limitation to biogeochemical processes in tropical forest soils. Phosphorus limitation was pronounced in aerated environments with low mean annual rainfall, whereas low redox conditions or associated factors under high rainfall conditions may have a stronger impact on biogeochemical cycling than P availability.

高度风化土壤上的潮湿热带森林通常具有生物可利用磷 (P) 浓度低的特点。这些生态系统也经常经历低且波动的氧化还原条件。关于土壤氧化还原条件如何影响 P 可用性以及这可能如何反馈生物地球化学循环知之甚少。在这里，我们使用来自波多黎各潮湿热带降雨梯度的土壤来探索氧化还原对磷生物有效性和相关生物地球化学过程的影响。随着降雨量的增加，土壤碳 (C) 和结晶性差的铁 (Fe) 和铝 (Al) 矿物质的浓度至少增加了两倍，这反映了更潮湿的地方更强烈的厌氧条件和相关的分解下降。NaOH 可提取的有机形式的总磷池的比例通常也随着降雨量的增加而增加。₂生产。然而，厌氧过程，包括厌氧呼吸、铁还原和甲烷生成，仅在最干燥的地方随着磷的增加而增加。在最干燥地点的缺氧条件下，微生物生物量 C:P 比率随 P 修正而降低，这是该地点可能的微生物 P 限制的指标。在所有土壤中，微生物生物量 C 和 P 浓度在缺氧条件下都低于在有氧条件下，这表明缺氧条件可能比 P 浓度更能限制微生物。总的来说，我们的结果表明氧化还原条件调节了热带森林土壤生物地球化学过程中磷限制的程度。在年平均降雨量低的充气环境中，磷限制很明显，