Collaborative Research: Bioavailabilty of soil phosphorus in tropical forest soils: Is slowly cycling phosphorus accessible to plants and soil biota?

热带森林的植物生长速度是世界上最高的。热带植物在生长过程中，通过光合作用从大气中吸收大量的二氧化碳，并将其中相当一部分碳储存在它们的生物量中，最终储存在土壤中。此外，有证据表明，随着大气中二氧化碳浓度的上升，未来植物的生长将加速，吸收和储存更多的碳。然而，目前尚不清楚热带森林土壤中是否有足够丰富的其他植物养分，使植物能够像预测的那样生长。在热带地区，土壤磷(P)浓度通常很低，这种低磷浓度可能严重限制植物未来的生长。本研究将探讨植物如何从土壤中获取磷，以及植物实际可获取的磷形式。实验将探索植物根系、细菌和真菌如何从土壤中“挖掘”养分，并将确定能够获取土壤磷的特定微生物。这项工作将是第一批探索树木生长与不同形式土壤磷之间关系的研究之一，它将提高对生物磷有效性控制的理解，并将揭示热带土壤中磷限制对植物生长的普遍影响。此外，该项目将提高我们预测热带森林生产力未来增长率的能力，并可能导致热带农业土壤土壤肥力管理方式的改进。最后，这项研究将包括学生培训以及促进科学家和环境记者之间的互动。关于热带地区植物初级生产的营养限制的真实程度的知识仍然不完整，这在很大程度上反映了我们对生物有机体实际可利用的土壤P的形式的理解不足。拟议的研究将解决以下首要问题：传统上被认为在生物学上不可用的土壤磷(P)的形式实际上对植物和微生物是可用的吗？在热带低地的高风化土壤中，只有一小部分土壤磷以传统上被认为是生物可利用的形式存在；绝大多数存在于化学和/或物理保护的磷池中，这些磷池被认为是植物和土壤微生物无法获得的。然而，如果植物和土壤微生物能够有效地克服土壤磷利用率低，通过获取这些顽固性形式的磷，到目前为止，一直被认为是不可用的，那么热带地区磷限制的程度可能比目前生物地球化学理论预测的要小。拟议的研究包括在巴拿马的一组热带森林地点进行的一系列实地、实验室和温室试验。总的来说，这些计划中的实验旨在验证一个可行的假设，即传统上被认为不可用的P型实际上在生物学上是可用的。在实验数据的基础上，研究将最终形成一系列综合和建模活动，旨在探索土壤磷素有效性的变化如何影响生态系统到全球尺度的未来NPP速率。

Rates of plant growth in tropical forests are among the highest on earth. As they grow, tropical plants take up large amounts of carbon dioxide from the atmosphere during photosynthesis, and store a substantial proportion of that carbon in their biomass and ultimately in soil. In addition, there is some evidence that plant growth will accelerate in the future with rising atmospheric CO2 concentrations, taking up and storing more carbon. However, it is unclear whether other plant nutrients are sufficiently plentiful in tropical forest soils to allow plants to grow as much as is predicted. In the tropics, soil phosphorus (P) concentrations are generally very low and such low P concentrations could strongly limit plant growth in the future. This research will explore how plants acquire phosphorus from soil, and which forms of phosphorus are actually accessible to plants. Experiments will explore how plant roots, bacteria and fungi "mine" nutrients from the soil, and will identify the specific microorganisms capable of accessing soil P. This work will be among the first to explore relationships between tree growth and different forms of soil P, it will improve understanding of the controls on biological P availability, and it will shed light on how pervasive P limitation is to plant growth in tropical soils. In addition, the project will enhance our ability to predict future rates of tropical forest productivity and could lead to improvements in how soil fertility is managed in tropical agricultural soils. Finally, the research will involve student training as well as promoting interaction between scientists and environmental journalists.Knowledge of the true extent of nutrient limitation of plant primary production in the tropics remains incomplete, in large part reflecting our poor understanding of what forms of soil P are actually available to biological organisms. The proposed research will address the following overarching question: Are forms of soil phosphorus (P) that have traditionally been considered biologically unavailable actually available to plants and microorganisms? In the highly-weathered soils that dominate the lowland tropics, only a small fraction of total soil P resides in forms that are traditionally considered biologically available; the vast majority resides in more chemically and/or physically protected P pools that are presumed to be unavailable to plants and soil microbes. However, if plants and soil microbes can effectively overcome low soil P availability by accessing these recalcitrant forms of P that, until now, have been thought to be unavailable, then the extent of P limitation in the tropics could be less than current biogeochemical theory predicts. The proposed research includes a set of field, laboratory and greenhouse experiments conducted in a set of tropical forest sites in Panama. Together, the planned experiments have been designed to test the working hypothesis that P forms that have traditionally been viewed as unavailable are actually biologically available. Building on the experimental data, the research will culminate in a set of synthesis and modeling activities designed to explore how variations in soil P availability may affect future rates of NPP at ecosystem to global scales.