Spatial segregation, substrate and nutrient availability as limiting factors for subsoil C-turnover

空间隔离、基质和养分有效性作为底土碳周转的限制因素

• 批准号: 233441010
• 负责人: Professor Dr. Bernd Marschner
• 金额: --
• 依托单位: Geographisches Institut
• 依托单位国家: 德国
• 项目类别: Research Units
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/233441010?language=en
• 关键词: Spatial; segregation; substrate; nutrient; availability

The spatial heterogeneity of subsoil C distribution and fluxes is much higher than in topsoils due to the greater relevance of preferential flow paths, roots, and animal burrows for C-inputs. The spatial segregation of consumers and substrate therefore is more a rule than an exception in subsoils. Taken as an explanation for the observed homogenization effects and for slow turnover rates in subsoils, this implies that hot spots are rather static and "cold regions" remain uninhabited despite substrate availability for extended periods of time. The rhizosphere soil is such a hot spot where C-inputs alter SOC composition and stimulate microbial and enzyme activities. On the other hand, microbial activity in the subsoil appears to be limited by nutrient availability, as indicated by enzyme activity patterns and incubation experiments performed during the first phase. Fresh substrate inputs in the rhizosphere may thus provide energy for microorganisms to produce enzymes for acquiring these limiting nutrients, or they may aggravate N- and P-limitations and thus lead to the accumulation of root-borne organic matter in the rhizosphere. The main objective of the activities outlined in this proposal is to investigate the factors limiting the degradation of subsoil SOC and thus contribute to resolving the contradictory findings of relatively high mineralisation rates in incubation experiments despite the high apparent 14C age of subsoil SOC. The explanatory mechanism of spatial separation between consumers and substrates will be addressed by applying new imaging techniques for analysing spatial patterns of enzyme activities and substrate mineralization in undisturbed soil samples from different depths at various sites. Another focus of this project will be on the characterization of hotspots of microbial activity, mainly the rhizosphere, regarding enzyme patterns and factors stimulating or limiting mineralization processes at these micro-sites relative to the bulk soil. By determining these rhizosphere effects and their spatial extension, important input parameters for the rhizosphere module of the COMISSION model (PC) will be made available. The analysis of 14CO2 in long-term incubation experiments will reveal, if only recent SOC inputs are mineralized or also "old" SOC is labile under these conditions. We will analyze enzyme activities in the soil solutions that are collected at the Grinderwald observatories to determine their translocation into the subsoil. Finally, this project will contribute with its specific analytical tools to several other joint experiments of the research unit.

由于优先流动路径、根系和动物洞穴对碳输入的相关性更大，地下土壤碳分布和通量的空间异质性远高于表层土壤。因此，在底土中，消费者和基质的空间分离与其说是例外，不如说是规律。作为对观测到的均质化效应和下层土壤缓慢周转率的解释，这意味着热点是相当静态的，而“冷区”尽管有较长时间的基质可用性，但仍然无人居住。根际土壤是碳输入改变有机碳组成并刺激微生物和酶活性的热点。另一方面，正如酶活性模式和第一阶段进行的孵化实验所表明的那样，底土中的微生物活动似乎受到养分可用性的限制。因此，根际的新鲜底物输入可能为微生物提供能量，使其产生酶以获取这些限制性营养物质，或者它们可能加剧N和p的限制，从而导致根际有机质的积累。本提案中概述的活动的主要目标是研究限制地下土壤有机碳降解的因素，从而有助于解决孵育实验中相对较高矿化率的矛盾发现，尽管地下土壤有机碳的表观14C年龄很高。通过应用新的成像技术分析不同地点不同深度未扰动土壤样品中酶活性和底物矿化的空间模式，将解决消费者和底物之间空间分离的解释机制。这个项目的另一个重点将是微生物活动热点的特征，主要是根际，关于酶的模式和因素刺激或限制矿化过程在这些微点相对于大块土壤。通过确定这些根际效应及其空间扩展，将获得commission模型（PC）根际模块的重要输入参数。在长期培养实验中对14CO2的分析将揭示，如果只有最近的SOC输入是矿化的，或者“旧”SOC在这些条件下也是不稳定的。我们将分析在格林德沃天文台收集的土壤溶液中的酶活性，以确定它们在底土中的转运。最后，该项目将以其特定的分析工具为研究单位的其他几个联合实验做出贡献。