Decoupling above- from belowground litter decomposition and impacts on stabilization of soil organic matter with increasing aridity

随着干旱程度的增加，地上和地下凋落物分解的脱钩以及对土壤有机质稳定性的影响

• 批准号: 511741712
• 负责人: Professor Dr. Karsten Kalbitz
• 金额: --
• 依托单位: Max-Planck-Institut für Biogeochemie (MPI-BGC)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/511741712?language=en
• 关键词: Decoupling; above; belowground; litter; decomposition

Drylands cover large areas of the land surface and may continue to expand in the future due to climate change. Even though dryland soils have low organic carbon (OC) concentrations, they store a significant fraction of global soil OC stocks. However, predicting effects of increasing aridity on soil OC stocks is not yet possible because above- and belowground processes of litter decomposition and soil organic matter (SOM) stabilization are differently affected by aridity. Consequences of increasing aridity on abiotic processes, such as photochemical and thermal degradation, and consequences for SOM stabilization processes by aggregation and formation of mineral-associated organic matter (MAOM) are still unclear. The role of extracellular polymeric substances (EPS) is particularly unknown, as they can stabilize aggregates (increasing importance at drier conditions) and promote the formation of MAOM (increasing importance at wetter conditions). The overarching objectives of this project are to assess the differential response of above- and belowground litter decomposition to increasing aridity and to elucidate the consequences for SOM stabilization. We will take advantage of a unique steep gradient in precipitation found on common parent material in Israel. We hypothesize that increasing aridity results in increasing de-coupling of the mechanisms responsible for above- and belowground litter decomposition as well as SOM stabilization. Increasing aridity should slow down decomposition of belowground litter more than that of aboveground litter. Further, increasing precipitation should promote the formation of MAOM particularly from belowground litter whereas increasing aridity results in higher contribution of aggregation to SOM stabilization. We will study above- and belowground litter decomposition and SOM stabilization by applying 13C-labelled litter (shoots and roots) of an annual herbaceous plant along the aridity gradient. To account for the spatial heterogeneity in vegetation cover, we include areas under shrubs and inter-shrub herbaceous patches. The use of stable isotopes allows us to monitor litter decomposition and follow SOM formation under conditions as natural as possible along the gradient. We will measure 13CO2 fluxes in the field and combine these data with the incorporation of the 13C tracer into SOM fractions obtained by density fractionation, EPS, and aggregate stability. This will provide insights into stabilization mechanisms of SOM as a function of aridity and vegetation cover. This field study will be combined with laboratory-based experiments for getting deeper insights into the importance of abiotic processes for litter decomposition. Our complementary approach will improve our understanding of the controls of litter decomposition and SOM stabilization in semi-arid regions. This study will strongly improve the scientific base for soil C and earth system models in drying climates.

旱地覆盖了大面积的陆地表面，而且由于气候变化，今后可能继续扩大。尽管旱地土壤的有机碳浓度较低，但它们储存了全球土壤有机碳储量的很大一部分。然而，预测干旱增加对土壤有机碳储量的影响是不可能的，因为地上和地下的凋落物分解和土壤有机质（SOM）的稳定过程受到不同的干旱影响。干旱增加对非生物过程的影响，如光化学和热降解，以及有机质稳定过程中的聚集和矿物相关有机物（MAOM）的形成的后果仍然不清楚。胞外聚合物（EPS）的作用尤其未知，因为它们可以稳定聚集体（在干燥条件下增加重要性）并促进MAOM的形成（在潮湿条件下增加重要性）。该项目的总体目标是评估地上和地下凋落物分解的差异响应，以增加干旱和阐明SOM稳定的后果。我们将利用在以色列普通母质上发现的独特的降水陡梯度。我们假设，增加干旱的结果，负责地上和地下凋落物分解以及SOM稳定的机制，增加解耦。干旱增加减缓了地下凋落物的分解速度，而不是地上凋落物。此外，降水量的增加应促进MAOM的形成，特别是从地下凋落物，而增加干燥度的结果在更高的贡献，聚集SOM稳定。我们将研究地上和地下凋落物分解和有机质稳定应用13 C标记的一年生草本植物的凋落物（芽和根）沿着干旱梯度。考虑到植被覆盖的空间异质性，我们包括灌木和灌木间草本斑块下的区域。稳定同位素的使用使我们能够监测凋落物的分解，并遵循SOM的形成条件下尽可能自然沿着梯度。我们将测量13 CO2通量在现场和联合收割机这些数据与13 C示踪剂的掺入到SOM馏分密度分馏，EPS，和聚集体的稳定性。这将提供深入了解SOM作为干旱和植被覆盖的功能的稳定机制。这项实地研究将与实验室为基础的实验相结合，以更深入地了解凋落物分解的非生物过程的重要性。我们的补充方法将提高我们的理解控制凋落物分解和SOM稳定在半干旱地区。该研究将有力地完善干旱气候下土壤C和地球系统模型的科学基础。