Biological carbon stabilization and destabilization: peering into microbial hot spots to understand soil carbon turnover and terrestrial energy flows

人口增长、农业集约化和气候变化正威胁着全球粮食安全。需要了解土壤碳(C)的数量、组成和稳定性，以提高土壤肥力和农业生态系统的可持续性，并建立公平和透明的方法来评估部门对减缓气候变化的贡献。最近，人们把重点放在储存或隔离土壤C上。虽然这一目标对减缓气候变化至关重要，但重要的是要认识到土壤C不仅需要储存，而且还需要用于维持生态系统功能。植物光合作用是农业生态系统土壤新碳的主要来源，因此也是新能源的主要来源。土壤有机质的形成是由微生物介导的，微生物在分解过程中利用植物C释放能量和养分。了解这些微生物转化是至关重要的。土壤有机质是土壤肥力和生产力的核心。它含有支持植物生长的C和营养物质，为生物过程提供燃料，为负责的生物群提供栖息地，并缓冲短期压力（如营养失衡或干旱）。***微生物活动的热点，如植物残体表面和土壤团聚体中的微点，其活跃种群比散装土壤高20倍。热点产生于丰富的可用资源（例如C）。它们在时间上是动态的，很难在相关的时间和空间尺度上进行研究。为了优化碳循环过程和可持续的土壤管理，需要更好地了解微生物分类群或群落特征在进行分解中的作用。为了更好地了解富含碳的热点地区碳周转的微生物动力学，拟议的研究计划将通过三个项目专门研究土壤微生物如何作为碳流动的媒介，这些项目分别研究土壤碳稳定和不稳定的微生物生态学方面：1)研究不同农业土壤C热力利用效率与微生物群落组成的关系；2)以富C埋地土壤为模型系统，确定富C热点地区稳定C的指示微生物和SOM生物标志物；3)分析富C埋地土壤物理大小组分和团聚体的微生物群落和C转换，以更好地了解微生境作为稳定C的潜在热点的作用。***在土壤肥料管理中，氮(N)、磷(P)和钾(K)常量养分的相互关系是公认的。将碳明确纳入资源管理战略有可能大大提高肥料使用效率，并加强空气和水过滤、减缓气候变化和粮食生产等关键功能。换句话说，向CNPK管理框架的转变将更好地支持可持续土壤管理，并最终支持粮食安全。**

Burgeoning population, agricultural intensification and changing climate are threatening global food security. Understanding the amount, composition and stability of soil carbon (C) is needed to enhance soil fertility and agroecosystem sustainability and to establish a fair and transparent approach to evaluating sector contributions to climate change mitigation. Recently, great focus has been on storing or sequestering soil C. While this goal is critical to climate change mitigation, it is important to recognize that soil C not only needs to be stored, but also used to maintain ecosystem function. Plant photosynthate is the primary source of new C, and thus new energy, in agroecosystem soils. Formation of soil organic matter is mediated by microorganisms that utilize plant C during decomposition, releasing energy and nutrients. Understanding these microbial transformations is critical. Soil organic matter is at the heart of soil fertility and productivity. It holds C and nutrients that support plant growth, fuels biological processes, provides habitat for the biota responsible and buffers against short-term stresses (e.g. nutrient imbalance or drought). *** Hot-spots of microbial activity such as plant residue surfaces and microsites within soil aggregates have active populations up to twenty times higher than the bulk soil. Hot spots arise from abundant resource availability (e.g. C). They are temporally dynamic and difficult to study at relevant scales of time and space. Improved understanding of the roles of microbial taxa or community traits that perform decomposition is needed to optimize C cycling processes and for sustainable soil management. To better understand microbial dynamics of C-turnover in C-rich hot spots, the proposed research program will specifically examine how soil microorganisms act as agents of C flows through three projects which address separate, but related aspects of microbial ecology of soil C stabilization and destabilization: 1) a survey of relationships between thermodynamic efficiency of C use and microbial community composition in different agricultural soils, 2) use C-rich buried soils as a model system to identify indicator microorganisms and SOM biomarkers for C-stabilization in C-rich hot-spots, 3) profile microbial communities and C turnover in physical size fractions and aggregates of these C-rich buried soils to better understand the role of microhabitats as potential hot-spots of C stabilization. *** The interrelatedness of macronutrients nitrogen (N), phosphorus (P) and potassium (K) is acknowledged in soil fertilizer management. Explicit integration of C into resource management strategies has the potential to greatly enhance fertilizer use efficiency and to bolster critical functions of air and water filtration, climate change mitigation and food production. In other words, a shift toward a CNPK management frameworks will better support sustainable soil management and ultimately, food security. **