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

热带森林中的植物生长速度是地球上最高的之一。随着热带植物的生长，它们在光合作用过程中会从大气中吸收大量二氧化碳，并将其中相当大一部分碳储存在它们的生物量中，最终储存在土壤中。此外，有一些证据表明，随着大气中二氧化碳浓度的上升，植物的生长将会加速，吸收和储存更多的碳。然而，目前还不清楚热带森林土壤中的其他植物养分是否足够丰富，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，这种低磷浓度可能会严重限制植物未来的生长。这项研究将探索植物如何从土壤中获取磷，以及植物实际上可以获得哪些形式的磷。实验将探索植物根、细菌和真菌如何从土壤中“开采”养分，并将确定能够获得土壤磷的特定微生物。这项工作将是首批探索树木生长与不同形式土壤磷之间的关系的工作之一，它将增进对生物磷有效性控制的理解，并将揭示热带土壤中普遍存在的磷限制对植物生长的影响。此外，该项目将增强我们预测未来热带森林生产率的能力，并可能导致热带农业土壤中土壤肥力管理的改进。最后，这项研究将涉及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磷的了解不足。拟议的研究将解决以下主要问题：传统上被认为是生物上不可用的各种形式的土壤磷(P)实际上对植物和微生物是可用的吗？在热带低地的高度风化土壤中，只有一小部分土壤总磷以传统上被认为是生物可利用的形式存在；绝大多数存在于更具化学和/或物理保护的磷库中，这些库被认为是植物和土壤微生物不能利用的。然而，如果植物和土壤微生物能够通过获取这些到目前为止被认为是不可用的顽固形态的磷，有效地克服土壤磷的低有效性，那么热带地区的磷限制程度可能会比目前的生物地球化学理论预测的要小。这项拟议的研究包括在巴拿马的一系列热带森林地点进行的一系列田间、实验室和温室实验。总而言之，计划中的实验旨在测试一个有效的假设，即传统上被视为不可用的P形式实际上在生物上是可用的。在实验数据的基础上，这项研究将在一系列综合和建模活动中达到高潮，旨在探索土壤磷有效性的变化如何影响未来生态系统到全球范围内的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.