Resource partitioning for phosphorus (P) in a P-limited plant community: preference for different soil P sources among co-occurring species

让许多物种共存的机制长期以来一直引起科学家的兴趣。资源分配就是这样一种机制，它允许物种共享资源，从而减少它们之间的竞争，从而促进共存。在植物中，这可能发生在物种共享一种营养素的情况下，这种营养素的供应有限，因为它们对不同形式的营养素有偏好。然而，尽管磷（P）是一种限制性营养素在世界上大约一半的植物群落，种间差异的偏好不同的P形式从来没有被证明，因此存在的P分配仍然是未知的。此外，P分配在驱动植物群落结构中的潜在作用也被研究过。这是一个重大的疏忽，因为（i）植物群落中普遍存在磷限制，（ii）磷限制系统通常具有较高的植物多样性，但不知道磷分配是否有助于这种多样性，以及（iii）鉴于土壤中不同形式的磷的高度多样性以及植物对土壤磷的许多适应性，可能会发生磷分配。分配和建立其机制基础，将提供一个根本性的进步，我们的理解的重要性，资源分配，通过展示其运作，通过一个最常见的限制营养素。这将实现使用P有限的草地作为一个模型系统。不同的33 P放射性同位素标记的P的形式代表一些主要的土壤P库将提供给共生植物物种的缩影，以确定哪些物种表现出偏好的P的形式。由于P分区建议通过植物的能力，以访问不同水平的生物利用度池种间差异进行操作，我们将使用P源，从高生物利用度难治性的形式。因此，我们将提供以下磷源：（i）正磷酸盐-直接被植物根部吸收，但在土壤中含量很小;（ii）DNA，生物利用度比磷酸盐相对较低，但生物利用度比磷酸盐高;（iii）肌醇磷酸盐，一种丰度高但生物利用度低的有机源。重要的是，从不同形式的磷的吸收将与土壤中天然存在的这些形式的浓度分析相结合，从而可以量化从天然存在的和标记的池中的总吸收，并允许正确确定对不同形式的真正偏好。将量化从这些磷源吸收的植物包括（i）具有特殊根系适应性的莎草，其可以增强对难治性磷的获得，（ii）具有菌根共生体和根系分泌物的草，其可以增强对一些难治性磷的获得，（iii）非─一种豆科杂类草，与菌根共生，但根系粗糙，可能表现出较低的获得难降解磷的能力，并对更多的磷有偏好生物可利用的形式，（iv）豆科植物，鉴于其高P需求，可能显示出对非常生物可利用的P的偏好，以及（v）非菌根的杂类草，因此可能显示出对非常生物可利用的P的最大偏好。总体而言，因此，我们预测这些物种对不同形态的磷表现出偏好，从而为磷的资源分配提供了第一个证据。更详细的工作的跳板P分区的重要性（详细的“学术资料”）。然而，我们认为这种更广泛（和昂贵）的工作首先需要概念验证，以优先使用不同的P形式的共存物种，因此我们集中小额赠款申请。

The mechanisms that allow many species to co-exist have long interested scientists. Resource partitioning is one such mechanism that allows species to share resources and so reduces competition between them and hence promotes co-existence. In plants, this may occur where species share a nutrient that is in limited supply by having preference for different forms of that nutrient. However, despite phosphorus (P) being a limiting nutrient in approximately half the world's plant communities, interspecific differences in preference for different P forms has never been demonstrated and so the existence of P partitioning remains unknown. Moreover, the potential role of P partitioning in driving plant community structure has bever been investigated. This is a major oversight, given (i) the prevalence of P limitation in plant communities, (ii) that P limited systems often have high floristic diversity but it is not known whether P partitioning contributes to that diversity, and (iii) that P partitioning is likely to occur given the high diversity of different forms of P in soil and the many adaptations that plants have to access soil P. Proving the existence of P partitioning and establishing its mechanistic basis would provide a fundamental advance in our understanding of the importance of resource partitioning by demonstrating its operation through one of the most commonly limiting nutrients. This will be achieved using a P limited grassland as a model system. Different 33P radioisotope labelled P forms representative of some major soil P pools will be supplied to microcosms of co-occurring plant species to determine which species show preference for which P forms. Since P partitioning is proposed to operate through interspecific differences in plants' abilities to access pools of different levels of bioavailability, we will use P sources ranging from highly bioavailable to refractory forms. We will therefore supply the P sources of (i) orthophosphate - which is directly taken up by plant roots but occurs in very small quantities in soil, (ii) DNA, relatively less bioavailable than phosphate but more bioavailable than (iii) inositol phosphate, an organic source of high abundance but low bioavailability. Importantly, uptake of P from different forms will be combined with analyses of concentrations of those forms naturally occurring in soil, so that total uptake from the naturally occurring and labelled pools can be quantified and allowing true preference for different forms to be properly determined. The plants for which uptake from these P sources will be quantified include (i) a sedge with specialist root adaptations that may enhance access to refractory P, (ii) a grass with mycorrhizal symbioses and root secretions that that may enhance access to some refractory P, (iii) a non-legume forb with mycorrhizal symbioses but coarse root systems that may show less ability to access refractory P and some preference for more bioavailable forms, (iv) a legume, that may show preference for very bioavailable P given their high P demand, and (v) a forb that is non-mycorrhizal and so may show the greatest preference for very bioavailable P. Overall, we therefore predict these species to show preference for different P forms and therefore provide the first evidence for resource partitioning of P. This research will provide a springboard for more detailed work on the importance of P partitioning (detailed in 'academic beneficiaries'). However, we believe such more extensive (and expensive) work first needs proof-of-concept for the preferential use of different P forms by co-occurring species, hence our focussed small grant application.