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）及其伴生凋落物是有机碳（OC）和氮（ON）最大的主动循环库。由于土壤既是碳汇又是碳源，因此对凋落物OM向SOM转化的控制机制及其在土壤中的稳定性的详细、机制理解对于准确解释大气、陆生植物和土壤碳库之间的变化平衡至关重要。在大陆中部和北美北部的森林中，人们越来越意识到大型食腐无脊椎动物，特别是蚯蚓（EW）对凋落物腐烂动力学和稳定SOM的相关性质的影响。有充分证据表明，蚯蚓引入原生EW很少或没有EW的森林的影响包括有机层的枯竭、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，蚯蚓的活性及其对酶活性、微生物群落结构和植物生物聚合物变化的反馈，通常不是影响SOM稳定性的考虑因素之一。本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侵入性EW活动和摄食习惯的差异如何与同一温带森林中不同地点凋落物化学组成、矿物学和微生物酶活性的差异相互作用，从而改变控制SOM稳定的物理、化学和生化保护机制的相对重要性。这项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，概括为以下四个问题：1)。EW是否促进凋落物的不同衰变路径，反映在其生物聚合物、元素和同位素组成上，从而可能影响其生化抗逆性和SOM稳定性？2)。植物/微生物OM的稳定程度和生物聚合物特性如何受到EW摄食习惯、初始凋落物化学以及土壤微生物和矿物组成的影响？3)鉴于已知蚯蚓会影响土壤结构和碳分配（即凋落物的迁移和与之相关的稳定微观结构的结合），在我们的野外地点，蚯蚓活动和凋落物化学的已知梯度将如何影响生物化学保护（即难降解生物聚合物）和/或物理和化学保护（即聚集和矿物相关）的SOM的特定来源、化学和数量？4)不同蚯蚓活动水平下的森林生态系统土壤有机碳（SOC）在陆地土壤碳库中的移动速率有何差异？这项工作将采用详细的分子、同位素、矿物学、生态学和微生物学方法，对具有强梯度电子束活动的系统中控制土壤有机质储存的过程进行机制理解。为了完成这些任务，我们组建了一个跨学科的团队，其中包括一名分子和稳定同位素生物地球化学家、一名土壤分子生态学家、一名土壤矿物化学家和一名蚯蚓生态学家，他们的综合专业知识非常适合研究这种生态变化对SOM稳定性的影响。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，缺乏关于这些问题的现有知识，我们应用的多学科视角，以及pi的资格。此外，这项工作对SOM建模社区有很大的潜力，他们正在努力进行物理上有意义的分析，从而允许SOM动力学建模。EW-凋落物-土壤系统在今天特别相关，因为该地区大多数已确定的EW物种？美国的森林是非本土的，预计在未来几十年里，它们将在地表温度上升和当地因素（如土壤迁移、丢弃的鱼饵和土地利用变化）的推动下进一步扩展到北部森林。从这项研究中获得的知识将有助于对北美东部落叶森林碳循环的主要驱动因素的总体理解。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，这对科学家和决策者都具有重要意义。此外，该项目将培养两名博士生和众多本科生，极有可能通过普渡大学吸引代表性不足的学生。美国国家科学基金会（nsf）资助的AGEP和美国原住民项目，SERC？s REU项目和约翰霍普金斯大学？教务长本科生研究奖，并将为高中教学模块提供信息。

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.