Will more productive Arctic ecosystems sequester less soil carbon? A key role for priming in the rhizosphere ('PRIME-TIME')

高纬度地区比其他地区变暖更快，因此成为气候变化研究的关键领域。此外，它们在地球系统的运作中发挥着至关重要的作用，在土壤有机质（SOM）中储存了大量的碳（C）。有很大的不确定性，这些碳存储的脆弱性，气候和土地利用的变化。以前的研究集中在气候变暖对植物生长和/或SOM动态的直接影响上，但越来越多的证据表明，植物-土壤相互作用使这些关系变得复杂。植物不仅控制凋落物输入（质量和数量），但也可能影响分解率，如果分配到“根际”（定义为在植物根部附近的土壤中的化学和微生物学的影响，他们的生长，呼吸和营养交换）的C量是正相关的微生物活性和分解的老更多的有机物质。这一过程被称为根际“引发”，尽管有人建议，它可能是决定生态系统C存储的关键，它仍然是非常少的了解，特别是在自然和半自然生态系统。由于气候变化和景观管理，特定群落的分布变化可能会对碳储量产生意想不到的影响。我们的研究团队在瑞典亚北极地区开展的工作表明，从非生产性的石楠林生态系统到生产力更高的落叶林的转变可能会导致土壤中碳的反直觉净损失。这种反应是不充分的模拟碳循环模型，不考虑植物根际土壤相互作用。相反，大多数模拟预测，如果高纬度地区的生产力提高，碳储存量将大幅增加。这项建议将确定植物（和相关的菌根）功能成分的变化对SOM的动态的影响。具体来说，我们将调查的后果，从苔原石南高灌木群落和落叶林地在瑞典北极地区的转变。我们将使用新的实验方法相结合，在现场和实验室，量化和了解根际引发效应（RPEs）的SOM动态的作用。在瑞典拉普兰的田野中，我们将使用实验（“环剥”;去除树皮，包括韧皮组织）来操纵整个山桦树林-苔原石楠交错带的根际，以减少有机C向根部的韧皮部运输。我们将结合联合收割机这与操纵根际过程使用“生长”核心（选择性地防止细根和/或真菌菌丝（丝）访问），以确定根，菌根真菌和异养（土壤分解）代谢的贡献。我们将部署最先进的微生物分子分析来评估处理对真菌群落结构的影响（特别是针对关键的菌根真菌群），以及新的C-同位素方法来量化RPEs.The项目产出有可能显着改善气候-地球化学相互作用的区域和全球建模，特别关注植物群落变化的间接影响。该项目与泛北极地区的“灌木林化”以及英国高地生态系统的“重新野生化”有关。'

High latitudes are warming faster than other regions, and thus serve as critical arenas for climate change studies. Furthermore, they play a pivotally important role in the functioning of the Earth system, storing significant amounts of carbon (C) in soil organic matter (SOM). There is major uncertainty over the vulnerability of these C stores to both climate and land-use change. Previous research has focussed on the direct effects of warming on plant growth and/or SOM dynamics in isolation, but there is increasing evidence that plant-soil interactions complicate these relationships dramatically. Plants not only control litter inputs (both quality and quantity), but may also influence rates of decomposition if the amount of C allocated to the 'rhizosphere' (defined as the area of soil in the vicinity of plant roots in which the chemistry and microbiology is influenced by their growth, respiration, and nutrient exchange) is positively related to microbial activity and the breakdown of older more recalcitrant organic matter. This process is referred to as rhizosphere 'priming', and despite suggestions that it may be critical in determining ecosystem C storage, it remains extremely poorly understood, especially in natural and semi-natural ecosystems. Changes in the distribution of particular communities, which are already taking place due to climate change and landscape management, may have unexpected impacts on C storage. Work carried out by our research team in the Swedish sub-Arctic suggests that transformations from unproductive heathland ecosystems into more productive deciduous forests could result in counterintuitive net LOSSES of C from soils. Such responses are inadequately simulated by C-cycle models which do not take into account plant-soil interactions in the rhizosphere. Rather, most simulations predict C storage will increase substantially if productivity increases at high-latitudes. This proposal will determine the impacts of shifts in plant (and associated mycorrhizal) functional composition on the dynamics of SOM. Specifically we will investigate the consequences of a shift from tundra heath to tall shrub communities and deciduous woodland in the Swedish Arctic. We will use a combination of novel experimental approaches, in both the field and the lab, to quantify and understand the role of rhizosphere priming effects (RPEs) for SOM dynamics. In the field in Swedish Lapland we will manipulate the rhizosphere across the mountain birch forest-tundra heath ecotone using experiments ('girdling'; removal of bark, including phloem tissues) to reduce phloem transport of organic C to the roots. We will combine this with manipulating rhizosphere processes using 'in-growth' cores (which selectively prevent fine root and/or fungal hyphal (filament) access) to determine the contributions of roots, mycorrhizal fungi and heterotrophic (soil decomposer) metabolism. We will deploy state of the art microbial molecular analyses to assess the impact of the treatments on fungal community structure (specifically targeting key mycorrhizal fungal groups), and novel C-isotope approaches to quantify RPEs.The project outputs have the potential to improve significantly regional and global modelling of climate-biogeochemical interactions, with a particular focus on the indirect effects of shifting plant communities. The project has relevance for the pan-Arctic 'shrubification', as well as for UK upland ecosystems being managed for 're-wilding.'