Microbial regulation of organic matter decomposition at the regional scale

本项目通过引入地下群落与气候之间的动态反馈，为改进生物地球化学模型（如DAISY-EXPERTN）的参数化提供了分析基础。鉴于我们目前测量了涉及碳循环的土壤微生物过程的温度敏感性函数的季节和区域变化，我们将在项目的下一阶段关注特定群体的周转时间（细菌和真菌）和碳流入特定群体的土壤微生物及其季节性基质利用效率。利用13C-PLFA和13c -麦角甾醇谱分析方法，在两个地区（斯瓦本Alb和Kraichgau）的种植地块上建立一个微观实验，研究细菌和真菌生物量的周转时间。我们假设真菌比细菌储存新吸收的碳（13C信号）的时间更长，因为它们的周转时间较慢。在野外实验中控制资源的输入将使我们能够分别研究细菌和真菌中的碳流。我们将选择以下标记化合物：(1)13C葡萄糖（主要是细菌C结合）和(2)13C酚/木质素前体（主要是真菌C结合）。我们将在一年四次（早春、夏季、秋季和深秋）建立微观世界。微生物效率将通过测量13c -底物与不同微生物生物量组分（Cmic、细菌和真菌PLFAs、麦角甾醇）的结合以及13CO2在安装微生物培养液后48小时内的损失来评估。我们的结果将被项目合作伙伴用于检查多室碳模型（例如CN DAISY）对改变的微生物生长效率的敏感性。此外，我们将测试以下哪些因素：基质质量、特定地点的微生物分解者群落或非生物土壤性质是区域尺度上凋落物分解空间变化的主要驱动因素。

Our project provides the analytical basis for improving the parameterisation of biogeochemical models (e.g., DAISY-EXPERTN) by introducing dynamic feedbacks between belowground communities and climate. Whereas we currently measure seasonal and regional variation of temperature sensitivity functions of soil microbial processes involved in carbon cycling, we will focus on group specific turnover times (bacteria and fungi) and flow of carbon into specific groups of soil microorganisms and their seasonal substrate use efficiency during the next phase of the project.A microcosm experiment will be established in cropped plots at both regions (Swabian Alb and Kraichgau) to study the turnover times of bacterial and fungal biomass using the 13C-PLFA and 13C-ergosterol profiling approach. We hypothesise that fungi store newly assimilated carbon (13C signal) for a longer period than bacteria due to their slower turnover times. Manipulating the input of resources in a field experiment will allow us to investigate separately the C flow through bacteria and fungi. We will choose the following labelled compounds: (1) 13C glucose (to account for mainly bacterial C incorporation) and (2) 13C phenol/lignin precursors (to account for mainly fungal C incorporation). We will establish the microcosms four times a year (early spring, summer, autumn and late autumn). Microbial efficiency will be assessed by measuring 13C-substrate incorporation into different components of the microbial biomass (Cmic, bacterial and fungal PLFAs, ergosterol) and loss as 13CO2 in the field for up to 48 hours after installation of the microcosms. Our results will be used by project partners to examine the sensitivity of multi-compartment carbon models (e.g. CN DAISY) to altered microbial growth efficiency. In addition, we will test which of the following: substrate quality, site specific microbial decomposer communities, or abiotic soil properties, is the dominant driver of spatial variation in litter decomposition at the regional scale.