Microbial regulation of organic matter decomposition at the regional scale

我们的项目通过引入地下群落和气候之间的动态反馈，为改进生物地球化学模型(例如DAISY-EXPERTN)的参数化提供了分析基础。鉴于目前我们测量参与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，在项目的下一阶段，我们将重点关注特定土壤微生物组的特定周转时间(细菌和真菌)和流入特定土壤微生物组的碳及其季节性底物利用效率。将在这两个地区(Swabian Alb和Kraichgau)的作物地块中建立一个微型实验，利用13C-PLFA和13C-麦角甾醇剖面法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更慢。在田间试验中操纵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(主要用于细菌C掺入)和(2)13C苯酚/木质素前体(主要用于真菌C掺入)。每年创建四次微观世界(早春、夏日、秋季、晚秋)。微生物效率将通过测量13C底物掺入微生物生物量的不同成分(CMIC、细菌和真菌PLFA、麦角甾醇)以及安装微型宇宙后长达48小时的田间13CO2损失来评估。我们的结果将被项目合作伙伴用来检验多室碳模型(例如CN DAISY)对改变微生物生长效率的敏感性。此外，我们将测试以下哪一项是区域尺度上凋落物分解空间差异的主要驱动因素：基质质量、特定地点的微生物分解者群落或非生物土壤属性。

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.