Collaborative Research: Investigating the soil-earthworm-litter system controls on the stabilization of soil organic matter in Eastern deciduous forests

摘要土壤有机质（SOM）和凋落物是土壤中最大的有机碳（OC）和氮（ON）循环库。由于土壤作为一个汇和碳源，一个详细的，机械的理解的控制转换凋落物有机质，其在土壤中的稳定性是至关重要的，以准确地占大气，陆生植物和土壤碳库之间的平衡变化。在中部大陆和北方北美森林中，食草大型无脊椎动物，特别是蚯蚓（EW），对凋落物腐烂动力学和相关性质的稳定SOM的影响有越来越多的认识。有充分证据表明，将ECO 2引入到很少或没有天然EW的森林中的影响包括有机层的耗尽，森林地面凋落物，可溶性营养物质的损失，以及矿物和有机层的混合。然而，令人惊讶的是，生物活性，其反馈酶活性，微生物群落结构，和植物生物聚合物的改变，通常不是一个考虑因素适用于SOM稳定的影响。该提案旨在记录和量化这些保护机制如何在受不同程度电子战活动影响的自然和实验系统中相互作用。我们的重点主要是确定入侵EW活动和食性的差异如何相互作用的凋落物的化学成分，矿物学和微生物酶活性的差异，在同一温带森林的位置之间改变的相对重要性的物理，化学和生化保护机制控制SOM稳定。这个跨学科的合作提案提出了一系列假设和实验，以测试EW-凋落物-SOM动态的基本组成部分，总结在以下四个问题中：1）。EW促进凋落物不同的衰变路径，反映在其生物聚合物，元素和同位素组成，这可能会影响其生化降解，从而SOM稳定？2）。EW投料中植物/微生物OM的稳定程度和生物聚合物特性将如何受到EW饲养习惯、初始凋落物化学以及土壤的微生物和矿物组成的影响？3)蚯蚓会影响土壤结构和碳分配（即，凋落物移位和将其铸件与相关的稳定微结构结合到土壤中）在我们的田间站点上，生物活性和凋落物化学的已知梯度将如何影响特定的来源，化学，以及受到生物化学保护（即难熔生物聚合物）和/或受到物理和化学保护（即聚集和矿物缔合）的SOM的量？4)不同植被活动水平的森林生态系统在其土壤有机碳（SOC）通过陆地土壤碳库的移动速率方面有何不同？这项工作将采用详细的分子，同位素，矿物学，生态学和微生物的方法来开发控制土壤有机质存储在一个系统中的EW活动的强烈梯度的过程的机械理解。为了完成这些任务，我们已经组装了一个跨学科的团队，其中包括分子和稳定的同位素地球化学家，土壤分子生态学家，土壤矿物化学家，和土壤生态学家的综合专业知识非常适合调查这种生态变化的影响，对SOM的稳定性。这一建议的智力价值在于这些因素对土壤碳循环的重要性，缺乏现有的知识，这些问题，我们应用的多学科的角度来看，和资格的PI。此外，这项工作具有显着的潜力，有利于SOM建模社区，这对物理意义的分析，允许SOM动态建模的斗争。EW-凋落物-土壤系统是特别相关的今天，作为最确定EW物种在这一地区？中国的森林是非本地的，预计在未来几十年内，由于地表温度上升和当地因素，如土壤迁移、废弃的鱼饵和土地使用变化，它们将进一步扩展到北方森林。从这项研究中获得的知识将有助于对北美东部落叶林碳循环的主要驱动因素的普遍了解。这项工作的更广泛影响包括加强对蚯蚓在推动北美森林土壤过程和生物地球化学循环变化中的作用的理解，这对科学家和政策制定者都具有重要意义。此外，该项目还将培养两名博士。学生和众多的本科生，有很大的潜力，以吸引代表性不足的学生通过普渡？美国国家科学基金会资助的AGEP和美洲原住民计划，SERC？约翰霍普金斯大学的REU项目？教务长本科研究奖，并将提供信息的高中教学模块。

ABSTRACTSoil organic matter (SOM) and associated litter represents the largest actively cycling pool of organic carbon (OC) and nitrogen (ON). Because soil acts as both a sink and a source for carbon, a detailed, mechanistic understanding of the controls on the conversion of litter OM to SOM, and its stability in soil is critical to accurately account for the changing balance between the atmospheric, terrestrial plant, and soil carbon reservoirs. In mid continent and northern North American forests there is an increasing awareness of the effect that detritivore macroinvertebrates, specifically earthworms (EW), have on litter decay dynamics and the associated nature of stabilized SOM. Well-documented effects of earthworm introduction into forests with few or no native EW include the depletion of organic horizons, forest floor litter, loss of soluble nutrients, and mixing of mineral and organic horizons. Surprisingly, however, earthworm activity, with its feedbacks to enzymatic activity, microbial community structure, and plant biopolymer alteration, is generally not one of the considerations applied to influences on SOM stabilization. This proposal seeks to document and quantify how these protective mechanisms interact in natural and experimental systems impacted by different degrees of EW activity. Our focus is primarily on identifying how differences in invasive EW activity and feeding habit interact with differences in litter chemical composition, mineralogy, and microbial enzyme activity among locations in the same temperate forest to alter the relative importance of physical, chemical, and biochemical protection mechanisms controlling SOM stabilization. This interdisciplinary, collaborative proposal presents a series of hypotheses and experiments to test fundamental components of the EW-Litter-SOM dynamics as summarized in the following four questions: 1). Do EW promote a different decay path for litter, reflected in its biopolymer, elemental, and isotopic composition, that might impact its biochemical recalcitrance and thus SOM stabilization? 2). How will the degree of stabilization and the biopolymer character of plant/microbial OM incorporated in EW casts be influenced by EW feeding habit, initial litter chemistry, and the microbial and mineral composition of soil? 3) Given that earthworms are known to impact soil structure and carbon allocation (i.e. litter translocation and incorporation of their casts with associated stable microstructures into soil) how will the known gradient in earthworm activity and litter chemistry across our field sites impact the specific source, chemistry, and amount of SOM that is biochemically protected (i.e. refractory biopolymers) and/or physically and chemically protected (i.e. aggregated and mineral associated)? 4) How will forest ecosystems at different levels of earthworm activity differ in the rate at which its soil organic carbon (SOC) moves through the terrestrial soil carbon reservoir? This work will employ detailed molecular, isotopic, mineralogical, ecological and microbiological methods to develop a mechanistic understanding of the processes that control soil organic matter storage in a system with a intense gradient in EW activity. To accomplish these tasks we have assembled an interdisciplinary team that includes a molecular and stable isotope biogeochemist, a soil molecular ecologist, a soil mineral-chemist, and an earthworm ecologist whose combined expertise is well suited to investigate the impacts of this ecological change on the stability of SOM. The intellectual merit of this proposal rests on the importance of these factors for soil carbon cycling, the lack of existing knowledge about these questions, the multidisciplinary perspective we apply, and the qualifications of the PIs. Additionally, this work has significant potential to benefit the SOM modeling community, which struggles for physically meaningful analyses that permit modeling of SOM dynamics. The EW-litter-soil system is particularly relevant today as most identified EW species in this region?s forests are non-native, and it is anticipated that over the next few decades they will expand farther into northern forests driven by rising surface temperatures, and local factors, e.g. soil transport, discarded fishing bait, and land use change. Knowledge gained from this study will contribute to the general understanding of major drivers in carbon cycling in Eastern deciduous forests of North America. The broader impacts of this work include the enhanced understanding of the role earthworms in driving change in north American forest soil processes and biogeochemical cycles that will be of great significance to both scientists and policy-makers. Additionally, the project will educate two Ph.D. students and numerous undergraduates, with great potential to attract underrepresented students through Purdue?s NSF-Funded AGEP and Native American programs, SERC?s REU program, and Johns Hopkins? Provost Undergraduate Research Award and will provide information for a high school teaching module.