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因素之一是世界上最大的陆地碳库之一土壤如何对环境变化作出反应。土地利用和土地覆盖的变化，如砍伐森林用于农业或牧场，或放弃农业后的森林再生，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。过去的人类活动可以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景观所覆盖，很少有区域尺度的土壤碳评估纳入历史土地利用。该项目将重点研究历史和环境因素如何影响热带土壤中的碳储量及其对干扰的脆弱性。热带地区正在经历土地覆盖和人口增长的动态变化，但我们对热带土壤如何响应全球变化的理解仅限于少数土壤环境，这些土壤环境不能代表全球热带地区。拟议中的实地研究将在美国加勒比海的波多黎各岛进行。波多黎各是研究热带地区环境和人为因素之间相互作用的一个模式系统，因为它代表了气候区域、生态系统和土壤类型的多样性。拟议的教育活动将向学生提供跨学科的研究和职业技能训练以及实地经验，并将增加代表性不足的社区，特别是妇女和西班牙裔学生参与地理和地球科学。与机构科学家的合作将促进向管理人员和决策者广泛传播研究成果。该项目旨在测量过去人类活动对热带土壤碳动态的遗留影响，利用波多黎各一个特殊的自然实验室，该实验室拥有丰富多样的地质基质、降水梯度和充分记录的土地利用历史。该项目将通过收集新数据和整合存档数据来量化不同土地利用方式下的碳储量（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产对土壤碳的影响程度和持久性。提高对土壤类型、气候和土地利用对土壤有机质保持影响的机理认识，将通过研究不同土壤碳库对干扰的敏感性和利用天然丰度放射性碳同位素测量碳储存有效性的物理分步方法来完成。这些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科学家之间的合作创造新的机会，特别是通过开发一门以人类主导的热带景观中的环境挑战为重点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.