Interactions of organic matter and microbial dynamics in pasture soils along management chronosequences

在南厄瓜多尔的安第斯山脉，天然森林经常被砍伐和焚烧变成牧场。通常，牧草被热带蕨菜取代，导致这片贫瘠的牧场被遗弃。拟议项目的主要目标是：1)评估土壤有机质、微生物活动和结构所显示的牧场肥力下降的时间点，以及能够为现有牧场土地的可持续利用制定有效措施的各自原因；2)深入了解土地利用引起的负责土壤有机质动员和固定的因素和机制的变化。第一个目标将通过将表层土壤中的养分有效性、微生物活动(SOC、总和净N矿化)和群落结构(PLFA分析)与取决于牧场年龄、施肥、管理和火制度的植被特征联系起来。为了达到我们的第二个目标，将使用一系列不同的分子表征方法(Py-GC/MS、核磁共振、BPCA、SEC-MALLS、δ13C-Signature、降解性)来确定不同类型土壤有机质(颗粒状、重质、抗H_2O_2和水可提取的有机质)的生化组成。有机质和微生物动力学之间的相互作用将通过多元统计分析来确定。随着牧场管理时间序列数据密度的增加和对热带山地土壤有机质稳定过程认识的提高，将改进用CENTERY模型模拟土壤有机质储量变化的方法。

In the South Ecuadorian Andes natural forests have often been converted to pastures by slash-and-burn. Frequently, the pasture grass is displaced by tropical bracken leading to the abandonment of this unproductive pastures. The main goals of the proposed project are 1) to assess the point in time of pasture fertility decline, as indicated by soil organic matter and microorganism activity and structure, and the respective reasons to be able to develop effective measures for the sustainable use of already existing pasture land and 2) to gain insight into land-use induced changes of factors and mechanisms responsible for the mobilization and sequestration of soil organic matter. The first goal will be achieved by connecting nutrient availability, microbial activity (SOC, gross and net N-mineralization) and community structure (PLFA analysis) in topsoils with vegetation characteristics depending on pasture age, fertilization, management and fire regime. To reach our second goal the biochemical composition of different fractions of soil organic matter (particulate, “heavy”, H2O2- resistant and water extractable organic matter) will be determined using a diverse array of molecular characterisation methods (Py-GC/MS, NMR, BPCA, SEC-MALLS, δ13C-signature, degradability). Interactions between organic matter and microbial dynamics will be identified with multivariate statistical analysis. The increased density of data along the pasture management chronosequence and an improved knowledge of stabilization processes of SOM in the tropical mountain soils will improve modelling of SOM stock changes with the CENTURY model.