Shrub-driven transformation of the alpine soil carbon cycle

世界各地的生态系统正在经历快速的植被变化，以应对气候变化。最普遍但研究最少的植被变化之一发生在世界高山地区，那里的气候变化速度几乎是北半球平均速度的两倍。再加上土地利用的变化，这导致了木质灌木向高山草原迅速而广泛的向上扩张，对这些脆弱的高海拔生态系统的功能产生了潜在的深远影响，但人们对此知之甚少。一个紧迫的不确定性涉及到灌木在高山草原改变土壤(C)循环过程的潜力，这意味着土壤C的储存和持久性。考虑到高山草原土壤代表着全球主要的碳库，而且即使土壤碳库容量的微小变化也可能对气候变化的碳循环反馈产生重大影响，解决这种不确定性的需求是非常紧迫的。应对这一挑战需要我们逐步改变对灌木驱动的土壤有机质(SOM)转化及其持久性的理解，SOM是决定土壤C对全球变化的响应的关键生态系统属性。我们假设，高寒草原广泛而快速的向上扩展灌木及其根部伴生的埃里样菌根真菌，触发了不同的根际途径，导致SOM分解和持久SOM的形成，从而稳定了土壤碳库，减少了未来气候变化下的土壤碳流失。我们还预计，这些获得和稳定土壤碳的途径将超过导致土壤碳流失的相反的根际途径，从而导致净碳获得。我们计划使用景观、地块和实验室研究与先进的稳定同位素、基因组学和生化方法的强大组合来验证我们的新假设，以询问高山草原根际驱动的SOM分解和C稳定的对比路径的相对作用。此外，我们在过去NERC资助的高山草原研究的基础上，包括在奥地利阿尔卑斯山的一个长期实验平台，我们借鉴了关于根际驱动过程调节土壤C持久性的途径的新概念和发现。我们的研究将通过识别新的机制开辟新的天地，通过这种新机制，快速和广泛的灌木扩张改变根际途径的平衡，调节高山草原土壤C的获得和损失，最终确定土壤C储存和C循环反馈。但它也将推动理解根际驱动过程作为土壤碳储存和持久性调节器的作用的前沿，这是一个快速发展但鲜为人知的科学领域，对全球碳平衡和减缓气候变化至关重要。

Ecosystems worldwide are experiencing rapid shifts in vegetation in response to climate change. One of the most pervasive, but poorly studied, vegetation shifts is occurring in alpine regions of the world, where climate change is taking place at almost double the rate of the northern hemisphere average. In combination with changes in land use, this is leading to the rapid and widespread upward expansion of woody ericaceous shrubs into alpine grasslands, with potential far-reaching, but poorly understood, consequences for the functioning of these fragile high-altitude ecosystems. A pressing uncertainty concerns the potential for ericaceous shrubs to transform processes of soil (C) cycling in alpine grasslands, with implications for soil C storage and persistence. The need to address this uncertainty couldn't be more urgent given that alpine grassland soils represent a major global C store, and because even small changes in their soil C storage capacity could have major implications for C-cycle feedbacks to climate change. Tackling this challenge requires a step change in our understanding of the mechanisms underpinning shrub-driven transformations of soil organic matter (SOM) and its persistence, a critical ecosystem property determining the response of soil C to global change.We posit that the widespread and rapid upward expansion of ericaceous shrubs and their root-associated ericoid mycorrhizal fungi into alpine grassland triggers distinct rhizosphere pathways that lead to the suppression of SOM decomposition and formation of persistent SOM, thereby stabilising the soil C pool and reducing soil C loss under future climate change. We also expect these pathways of soil C gain and stabilisation to outweigh opposing rhizosphere pathways that cause soil C loss, thereby leading to net C gain. We plan to test our novel hypotheses using a powerful combination of landscape, plot, and laboratory studies with advanced stable-isotope, genomics, and biochemical approaches to interrogate the relative roles of contrasting rhizosphere-driven pathways of SOM decomposition and stabilisation of C in alpine grassland. Moreover, we build on our past NERC funded research in alpine grasslands, including a long-term experimental platform in the Austrian Alps, and we draw on novel concepts and discoveries concerning the pathways by which rhizosphere-driven processes regulate the persistence of soil C. Our study will break new ground by identifying novel mechanisms by which rapid and widespread ericaceous shrub expansion alters the balance of rhizosphere pathways that regulate soil C gain and loss in alpine grasslands, ultimately determining soil C storage and C-cycle feedbacks. But also, it will push the frontiers of understanding the role of rhizosphere-driven processes as regulators of soil C storage and persistence, which is a fast moving, but poorly understood area of science of central importance to the global C balance and mitigation of climate change.