Rhizosphere Mediation of Biosphere-Climate Feedbacks – Assessing Blue Carbon Cycling under Climate Change

气候驱动的土壤非生物条件变化可直接影响微生物群落，从而影响碳和温室气体(GHG)向大气的排放。除了对土壤微生物碳循环的直接气候变化影响(CCES)外，植物对气候变化的反应可以作为CCES对土壤微生物群落的强烈的-有时是压倒的-中介。这些植物介导的效应在根际最为明显，并由植物的生理和形态性状表达决定。然而，植物性状、土壤微生物功能和碳通量之间的联系并不发达，这代表着在生态系统-气候反馈模型方面的关键知识缺口。我认为，植物对土壤微生物碳循环的影响在湿地生态系统中尤为重要，因为在湿地生态系统中，植物不仅控制微生物底物的供应，还通过向还原土壤系统提供氧气来调节电子受体的可用性。与此同时，湿地土壤微生物碳循环在气候系统中扮演着不成比例的大角色，因为低速率的微生物活动导致湿地封存了生物圈中最大的土壤有机碳(SOC)储量，如果气候变化释放温室气体，这将是一个巨大的潜在温室气体来源。该项目的中心目标是通过调查植物性状响应及其与土壤微生物群落的相互作用，了解植物在湿地SOC储量稳定性和温室气体排放方面的CCES调节机制。研究的重点将是潮汐湿地，即位于陆地和海洋交界处的半陆地生态系统，越来越多地认识到它们在“蓝碳”一词下对全球碳循环的巨大影响。这项工作包括四个互补性的子项目(SP)，从植物特性的角度评估土壤微生物碳循环。SP1将通过确定通过根际引发效应控制湿地SOC分解的植物特性，并确定引发效应与湿地总体温室气体排放的关系，提供机制基础。这些知识将用于解决战略文件2中该项目的核心问题：植物如何协调气候变化对湿地有机碳储量稳定性和温室气体排放的影响？SP2将沿着气候敏感的环境梯度量化植物性状和微生物碳循环之间的相互作用，重点关注个体植物水平的反应(即表型可塑性)和群落水平的反应。SP3将通过探索种群水平的反应(即种内基因变异)来补充这项工作，作为尚未被忽视的植物介导的CCE对土壤微生物碳循环的额外水平。合成的SP4将比较和总结实验SPS的结果，并将它们未来整合到湿地碳循环的数值模型中。

Climate-driven alterations in soil abiotic conditions can directly affect microbial communities and thereby carbon and greenhouse-gas (GHG) fluxes to the atmosphere. In addition to direct climate-change effects (CCEs) on soil microbial carbon cycling, plant responses to climate change can act as a strong –sometimes overriding– mediator of CCEs on soil microbial communities. These plant-mediated effects are most pronounced in the rhizosphere and are determined by plant physiological and morphological trait expressions. However, the link between plant traits, soil microbial functioning, and carbon fluxes is poorly developed, which represents a key knowledge gap in informing models of ecosystem-climate feedbacks. I argue that plant-mediated effects on soil microbial carbon cycling are particularly important in wetland ecosystems because here plants not only control the microbial substrate supply, they also regulate the availability of electron acceptors by providing oxygen to an reducing soil system. At the same time, wetland soil microbial carbon cycling plays a disproportionately large role in the climate system, because low rates of microbial activity have caused wetlands to sequester the largest soil organic carbon (SOC) stock in the biosphere, representing a vast potential source of GHG to the atmosphere if unlocked by climate change. The central objective of this Emmy Noether project is to understand the mechanisms by which plants mediate CCEs on wetland SOC stock stability and GHG emissions through investigations of plant-trait responses and their interactions with soil microbial communities. Studies will be focused on tidal wetlands, semi-terrestrial ecosystems at the interface of land and sea that have been increasingly recognized for their outsized leverage over the global carbon cycle under the term ‘blue carbon’. The work comprises four complementary subprojects (SPs) that assess soil microbial carbon cycling from a plant-trait perspective. SP1 will provide the mechanistic basis by identifying the plant traits that control wetland SOC decomposition via rhizosphere priming effects, and determine how priming effects relate to overall wetland GHG emissions. This knowledge will be applied to address the project’s central question in SP2: How do plants mediate the effects of climate change on wetland SOC stock stability and GHG emissions? SP2 will quantify the interactions between plant traits and microbial carbon cycling along climate-sensitive environmental gradients, focusing on individual plant-level responses (i.e. phenotypic plasticity) and community-level responses. SP3 will complement this work by exploring population-level responses (i.e. intraspecific genotypic variation) as a yet overlooked additional level of plant-mediated CCEs on soil microbial carbon cycling. The synthesis, SP4, will compare and summarize the findings of the experimental SPs and advance their future integration into numerical models on wetland carbon cycling.