Role of fungal communities in carbon and nutrient cycling in forest soils under elevated atmospheric CO2 concentrations

已知真菌群落在林地生态系统中发挥着重要作用，但对其多样性、功能以及对环境变化的可能反应仍知之甚少。该项目旨在通过调查伯明翰森林研究所自由空气二氧化碳富集点（BIFoR FACE）的菌根真菌群落来解决这些知识差距。BIFoR FACE是北方唯一的此类设施，是一项大规模的实验，使成熟的温带林地的斑块受到升高的CO2水平（约100%）的影响。550 ppm），目的是阐明未来大气CO2增加对这种生态系统的可能影响。虽然最初预计二氧化碳水平升高会促进树木生长，但据预测，这种生长促进可能相对短暂，因为土壤养分的可用性-在北方，主要是氮-从长远来看可能会受到限制。更全面的评估，这种“渐进的氮限制”（PNL）的假设要求考虑真菌群落外生菌根真菌，特别是可以提供大量的，否则无法获得的氮，以他们的植物宿主，虽然在何种程度上发生变化的不同物种和环境条件。一种可能的情况与一些经验支持是，在升高的CO2下，树木将投资更多的碳在其菌根共生体中，并从这些真菌中获得更多的氮作为回报，缓解PNL。相反，来自北方森林生态系统的实验证据表明，更多的碳从树木分配给菌根真菌可能导致更多的氮被锁定在增殖的菌根生物量，而不是被转移到树木宿主，从而加剧PNL。该项目将首先使用分子技术来表征存在于BIFoR FACE站点的升高和环境CO2地块中的菌根真菌群落，确定两种条件下群落组成的差异是否明显。然后，这将形成的基础上，调查可能的变化，在菌根营养物质的获取和转移下，CO2浓度升高，无论是通过社区组成的变化或改变功能在不同的条件下，从而连接菌根真菌的反应，CO2浓度升高，其更广泛的影响，在营养循环和树木生长。

Fungal communities are known to play influential roles in woodland ecosystems, yet much remains unknown about their diversity, functioning, and likely responses to environmental change. This project aims to address some of these knowledge gaps by investigating mycorrhizal fungal communities at the Birmingham Institute of Forest Research Free Air Carbon Dioxide Enrichment site (BIFoR FACE). The only facility of its kind in the northern hemisphere, BIFoR FACE is a large-scale experiment subjecting patches of mature temperate woodland to elevated CO2 levels (approx. 550 ppm) with the aim of illuminating likely effects of future increases in atmospheric CO2 on this kind of ecosystem. Though elevated CO2 levels are expected initially to enhance tree growth, it is predicted that this growth enhancement may be relatively short-lived as the availability of soil nutrients - in the northern hemisphere, primarily nitrogen - could become limiting in the longer term. A fuller appraisal of this "progressive nitrogen limitation" (PNL) hypothesis demands consideration of fungal communities as ectomycorrhizal fungi in particular can supply significant quantities of otherwise inaccessible nitrogen to their plant hosts, although the extent to which this occurs varies between different species and environmental conditions. One possible scenario with some empirical support is that under elevated CO2 trees will invest more carbon in their mycorrhizal symbionts and receive more nitrogen from these fungi in return, alleviating PNL. Conversely, experimental evidence from boreal forest ecosystems has suggested that greater allocation of carbon from trees to mycorrhizal fungi can lead to increased amounts of nitrogen being locked up in proliferating mycorrhizal biomass, rather than being transferred to tree hosts, thus exacerbating PNL. This project will use molecular techniques firstly to characterize the mycorrhizal fungal communities present in elevated- and ambient-CO2 plots at the BIFoR FACE site, determining whether differences in community composition are apparent between the two conditions. This will then form the basis for investigating possible changes in mycorrhizal nutrient acquisition and transfer under elevated CO2, whether through community compositional shifts or altered functioning under different conditions, thus connecting mycorrhizal fungal responses to elevated CO2 with their wider effects in terms of nutrient cycling and tree growth.