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

众所周知，真菌群落在林地生态系统中发挥着重要作用，但关于它们的多样性、功能和可能对环境变化的反应仍有许多未知之处。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浓缩场地(BIFoR Face)的菌根真菌群落来解决其中一些知识差距。BIFoR Face是北半球唯一的此类设施，它是一项大规模实验，将一片片成熟的温带林地置于较高的二氧化碳水平(约.550ppm)，目的是阐明未来大气二氧化碳增加对这类生态系统可能产生的影响。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，这种生长促进可能是相对短暂的，因为土壤养分的可用性--在北半球，主要是氮素--可能在较长期内变得有限。要更全面地评估这一“渐进氮素限制”(PNL)假说，需要考虑真菌群落，因为外生菌根真菌特别能够向植物宿主提供大量原本无法获得的氮，尽管这种情况发生的程度因物种和环境条件的不同而不同。一种可能的情况是，在二氧化碳浓度升高的情况下，树木将向它们的菌根共生体投资更多的碳，并从这些真菌那里获得更多的氮，从而缓解PNL。相反，来自北方森林生态系统的实验证据表明，从树木向菌根真菌分配更多的碳可以导致更多的氮被锁定在增殖的菌根生物量中，而不是转移到树木宿主，从而加剧PNL。该项目将首先使用分子技术来表征BIFoR Face站点高二氧化碳和环境二氧化碳地块中存在的菌根真菌群落，确定两种条件下群落组成是否存在明显差异。这将成为研究高二氧化碳下菌根养分获取和转移的可能变化的基础，无论是通过群落组成变化还是在不同条件下改变功能，从而将菌根真菌对高二氧化碳的反应与其在养分循环和树木生长方面的更广泛影响联系起来。

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.