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.

底土C分布和通量的空间异质性是远远高于表土，由于更大的相关性优先流路径，根，和动物洞穴的C-输入。因此，在底土中，消费者和基质的空间分离更多的是一种规则而不是例外。作为对所观察到的均匀化效应和底土中周转率缓慢的解释，这意味着热点是相当静态的，尽管基质可供使用很长一段时间，但“冷区”仍然无人居住。根际土壤是碳输入改变土壤有机碳组成、刺激微生物和酶活性的热点。另一方面，底土中的微生物活动似乎受到养分供应的限制，如第一阶段期间进行的酶活性模式和孵育实验所示。因此，在根际的新鲜基质输入可能会为微生物提供能量，以产生酶来获取这些限制性营养物质，或者它们可能会加剧N-和P-限制，从而导致根传有机物在根际的积累。本提案中概述的活动的主要目标是调查限制底土SOC退化的因素，从而有助于解决尽管底土SOC的表观14 C年龄较高，但培养实验中矿化率相对较高的矛盾结果。消费者和基质之间空间分离的解释机制将通过应用新的成像技术来分析空间差异来解决。不同地点不同深度原状土样中酶活性和基质矿化的模式。该项目的另一个重点将是表征微生物活动的热点，主要是根际，关于酶的模式和因素刺激或限制矿化过程中，在这些微网站相对于散装土壤。通过确定这些根际效应及其空间扩展，将提供COMISSION模型（PC）根际模块的重要输入参数。长期培养实验中的14 CO2分析将揭示，如果只有最近的SOC输入矿化或“老”SOC在这些条件下是不稳定的。我们将分析在格林德瓦观测站收集的土壤溶液中的酶活性，以确定它们转移到底土中。最后，该项目将利用其特定的分析工具为研究单位的其他几项联合实验做出贡献。