Low Redox Decreases Potential Phosphorus Limitation on Soil Biogeochemical Cycling Along a Tropical Rainfall Gradient
Low Redox Decreases Potential Phosphorus Limitation on Soil Biogeochemical Cycling Along a Tropical Rainfall Gradient
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DOI：
10.1007/s10021-021-00662-4
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发表时间：
2021-07
期刊：
影响因子：
3.7
通讯作者：
Yang Lin;A. Gross;W. Silver
中科院分区：
文献类型：
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作者：
Yang Lin;A. Gross;W. Silver
高度风化土壤上的潮湿热带森林通常具有低生物有效磷(P)浓度的特征。这些生态系统也经常经历低和波动的氧化还原条件。关于土壤氧化还原条件如何影响磷有效性以及这可能如何反馈生物地球化学循环，人们知之甚少。在这里，我们利用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)和低结晶铁（Fe）和铝（Al）矿物的浓度至少增加了两倍，这反映了湿润地区厌氧条件的增强和相关的分解下降。氢氧化钠可萃取有机形态的总磷库占总磷库的比例也普遍随着降雨量的增加而增加。在沿着梯度使用三个位点的实验室培养实验中，P修正增加了需氧co2的产生。然而，厌氧过程，包括厌氧呼吸、铁还原和甲烷生成，只在最干燥的地方随着P的修正而增加。在缺氧条件下，最干燥地点的微生物生物量C:P比值随着磷的增加而降低，这是该地点可能的微生物磷限制指标。在所有土壤中，缺氧条件下微生物生物量C和P浓度均低于缺氧条件下，这表明缺氧条件可能比磷浓度对微生物的限制更大。总的来说，我们的研究结果表明，氧化还原条件调节了热带森林土壤中磷对生物地球化学过程的限制程度。在年平均降雨量低的曝气环境中，磷的限制作用明显，而在高降雨量条件下，低氧化还原条件或相关因素对生物地球化学循环的影响可能比磷有效性更大。
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 CO2production. 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.