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

合作研究：调查土壤-蚯蚓-凋落物系统对东部落叶林土壤有机质稳定的控制作用

• 批准号: 0748442
• 负责人: Melissa McCormick
• 金额: $ 10.48万
• 依托单位: Smithsonian Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-09-15 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0748442&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigating; soil; earthworm

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.

土壤有机质(SOM)及其相关凋落物是最大的有机碳(OC)和氮(ON)主动循环库。由于土壤既是碳的汇，也是碳的源，对凋落物OM转化为SOM的控制及其在土壤中的稳定性的详细、机械的了解，对于准确解释大气、陆地植物和土壤碳库之间不断变化的平衡至关重要。在中大陆和北美北部的森林中，人们越来越认识到大型无脊椎动物，特别是蚯蚓(EW)对凋落物腐烂动态的有害影响，以及稳定的有机质的相关性质。将蚯蚓引入原生EW很少或没有的森林中，其有据可查的影响包括有机土层枯竭、森林地面凋落物、可溶性养分的损失以及矿物和有机土层的混合。然而，令人惊讶的是，蚯蚓活性对酶活性、微生物群落结构和植物生物聚合物变化的反馈作用，通常不是应用于影响土壤有机质稳定性的考虑因素之一。这项建议试图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活动和取食习性的差异如何与同一温带森林中不同地点的凋落物化学成分、矿物学和微生物酶活性的差异相互作用，以改变控制SOM稳定的物理、化学和生化保护机制的相对重要性。这一跨学科的合作提案提出了一系列假设和实验，以测试电子战-垃圾-SOM动力学的基本组成部分，概括为以下四个问题：1)。EW是否促进了凋落物的不同腐烂途径，反映在其生物聚合物、元素和同位素组成上，这可能会影响其生物化学顽固性，从而影响土壤有机质的稳定？电子战的摄食习性、初始凋落物化学以及土壤的微生物和矿物组成将如何影响电子战铸模中植物/微生物OM的稳定度和生物聚合物特性？3)鉴于蚯蚓已知会影响土壤结构和碳分配(即凋落物转移和将其铸型与相关的稳定微结构结合到土壤中)，我们田间场地的蚯蚓活动和凋落物化学的已知梯度将如何影响特定的来源、化学、4)不同蚯蚓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速率上有何不同？这项工作将使用详细的分子、同位素、矿物学、生态学和微生物学方法，从机理上理解在具有强烈EW活动梯度的系统中控制土壤有机质储存的过程。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调查这种生态变化对土壤有机质稳定性的影响。这一建议的学术价值在于这些因素对土壤碳循环的重要性、对这些问题的现有知识的缺乏、我们应用的多学科视角以及PIs的资格。此外，这项工作对SOM建模社区有很大的潜力，他们正在努力寻找物理上有意义的分析来允许对SOM动态进行建模。EW-凋落物-土壤系统在今天尤其重要，因为该地区已发现的大多数EW物种-S森林都是非本地物种，预计在未来几十年，由于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的变化，它们将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了解，这对科学家和政策制定者都将具有重要意义。此外，该项目将培养两名博士生和众多本科生，他们有很大的潜力通过普渡大学？S国家科学基金会资助的农业教育规划和美洲原住民项目、经济合作与合作委员会？S项目和约翰·霍普金斯大学？教务长本科生研究奖，并将提供高中教学模块的信息。