CAREER: Land Use and Environmental Controls on Soil Carbon in Human-Dominated Tropical Landscapes

预测地球气候变化的主要不确定性之一是，世界上最大的陆地碳库之一--土壤--对环境变化的反应。土地利用和土地覆盖的变化，如为农业或牧场用途砍伐森林，或在农业废弃后森林重新生长，影响土壤和大气之间的碳交换，对气候和土壤肥力产生影响。过去的人类活动会影响土壤中碳的数量和动态。尽管如此，而且越来越多的地球表面被人类改造的地貌覆盖，但很少有区域规模的土壤碳评估将历史上的土地使用纳入其中。该项目将重点研究历史和环境因素如何影响热带土壤中储存了多少碳及其易受干扰的问题。热带地区正在经历土地覆盖的动态变化和人口增长，但我们对热带土壤如何响应全球变化的了解仅限于少数不能代表全球热带的土壤环境。拟议的实地研究将在美国加勒比海的波多黎各岛上进行。波多黎各是研究热带环境和人为因素之间相互作用的模式系统，因为它代表了气候区域、生态系统和土壤类型的多样性。拟议的教育活动将为学生提供跨学科研究和职业技能培训以及实地经验，并将增加代表不足的社区对地理和地球科学的参与，特别是妇女和西班牙裔学生。与机构科学家的合作将促进向管理人员和政策制定者广泛传播研究成果。该项目旨在利用波多黎各一个特殊的自然实验室来衡量过去人类活动对热带土壤碳动态的遗留影响，该实验室具有丰富的地质底物、降水梯度和良好的土地利用历史。该项目将通过收集新数据和整合存档数据，量化不同土地利用、不同环境梯度、人类管理历史悠久的碳储量(数量和周转量)，以增加热带土壤环境的地理代表性。该项目将利用碳同位素深度剖面和野外时间序列，评估不同土壤类型的历史土地利用遗留影响随时间对土壤碳的影响的大小和持久性。将通过调查不同土壤碳库对干扰的敏感性的物理分级方法以及使用自然丰度的放射性碳同位素来衡量碳储存效率，从而从机理上更好地了解土壤类型、气候和土地利用对土壤有机质保留量的影响。研究和教育活动将为学生提供实地、实验室、地理空间和数据分析技能方面的培训。研究和教育活动的结合将为社会科学家和物理学家之间的合作创造新的机会，特别是通过开发侧重于人类主导的热带景观中的环境挑战的混合方法实地课程。

One of the major uncertainties in predicting changes in earth's climate is how one of the world's largest terrestrial carbon reservoirs, soils, responds to environmental change. Changes in land use and land cover, such as deforestation for agriculture or pasture use, or forest regrowth after agricultural abandonment, affect the exchange of carbon between soils and the atmosphere, with implications for climate and soil fertility. Past human activities can influence the quantity and dynamics of carbon in soils. Despite this, and the fact that an increasing proportion of the Earth's surface is covered by human-modified landscapes, few regional-scale assessments of soil carbon incorporate historical land use. This project will focus on how historical and environmental factors affect how much carbon is stored in tropical soils and its vulnerability to disturbance. Tropical regions are experiencing dynamic changes in land cover and increasing human population growth, yet our understanding of how tropical soils respond to global change is limited to few soil environments which are not representative of the global tropics. The proposed field research will take place in the U.S. Caribbean island of Puerto Rico. Puerto Rico is a model system to study interactions between environmental and human factors in the tropics because it represents a diversity of climatic regions, ecosystem and soil types. The proposed educational activities will provide students with interdisciplinary research and career skills training and field experience and will increase participation of underrepresented communities in geography and the geosciences, in particular women and Hispanic students. Collaborations with agency scientists will facilitate broad dissemination of research results to managers and policymakers. This project aims to measure legacy effects of past human activities on tropical soil carbon dynamics by taking advantage of an extraordinary natural laboratory in Puerto Rico with a rich diversity of geologic substrates, precipitation gradients, and well-documented land-use history. The project will quantify carbon storage (amount and turnover) under different land uses across environmental gradients with a long history of human management through the collection of new data and integration of archived data to increase the geographic representation of tropical soil environments. The project will evaluate the magnitude and persistence of historical land use legacy effects on soil carbon with time across different soil types using carbon isotope depth profiles and field chronosequences. Improved mechanistic understanding of the effects of soil type, climate and land use on soil organic matter retention to will be accomplished through physical fractionation approaches that investigate the sensitivity of different soil carbon pools to disturbance and the use of natural abundance radiocarbon isotopes to measure carbon storage effectiveness. The research and educational activities will provide students with training in field, lab, geospatial and data analysis skills. The integration of research and educational activities will create new opportunities for collaborations between social and physical scientists, especially through the development of a mixed-methods field course focused on environmental challenges in human-dominated tropical landscapes.