Effects of experimental warming, disturbances, and species interactions on tropical tree community demography

热带森林是世界上最多样化的生态系统，有些森林每公顷有数百种树种。这种多样性的维持被认为依赖于物种之间复杂的相互作用。然而，物种之间的关系和相互作用可以被气候变化和干扰（如飓风）所改变，这些干扰破坏了森林林下植被中控制幼苗和树苗相互作用的资源条件。该项目将结合遮荫屋实验和新的分子方法来研究成年树如何影响树冠下森林地面上物种幼苗之间的相互作用。除了解开干扰和变暖如何改变物种间关系的强度和方向之外，该项目还研究了植物如何通过从根尖分泌特定分子来控制植物间的相互作用。这些分泌物影响哪些微生物变得常见，而这些微生物反过来又影响幼苗的成功（通过促进有益微生物的积极作用，或通过促进致病微生物的消极作用）。具体地说，树冠树的幼苗将在不同密度的盆栽中生长，在遮荫的温室中，在一系列生长条件下生长，以模拟全球变暖和树冠覆盖度（光）的变化，这些变化是由于飓风摧毁了成年树冠而发生的。它们将以不同的密度组合和不同组合的田间微生物种植，这些微生物通常与不同种类的成年树的根有关。这项工作的结果将帮助我们更好地预测热带森林是否会在世界气候持续变化的情况下保持其高水平的多样性，以及飓风或旋风期间与冠层移除相关的光线变化如何改变物种关系。除了科学上的好处，该项目还将为代表性不足的学生提供教育和研究机会。该研究网站有一个建立成功的实习计划，其中最近毕业的大学生，主要来自波多黎各，提供了参与研究的机会。他们将有机会在项目中实习并从中获得研究经验。该小组还将与波多黎各的一个非营利组织合作，协调中小学生参观研究地点并了解该项目的实地考察。总的来说，这项工作将有助于科学界和更广泛的社区了解热带森林未来的样子。热带森林多样性的维持被认为依赖于复杂的物种相互作用，如互惠共生、捕食/病原体攻击和竞争，这些相互作用调节着幼苗动态和树种共存。在预计的气候变化和干扰制度下，这些多样性维持过程可能从根本上改变，但我们对这些因素如何单独或共同影响热带森林的生物多样性知之甚少。该项目建立并扩展了现有的红外变暖实验（热带气候变化响应实验，TRACE）。基于初步数据，研究小组假设密度依赖的强度和方向随着变暖和干扰而变化，因为物种相互作用的改变，如与菌根真菌（H1）的关联，植物可以通过根分泌物部分控制这些变化（H2）。这个为期2年的项目将遮荫室实验与组学方法相结合，以评估光、密度、小气候和微生物的变化如何影响不同森林物种的密度依赖性。具体来说，树种的幼苗将在花盆中生长，并接受两种土壤源处理（例如，tRACE站点的温暖土壤与对照土壤）、四种微生物处理（没有菌根真菌、没有病原体、没有微生物、对照）、三种密度（低、中、高）和两种光处理（低和高）。该研究的更广泛影响将分为三个主要重点：1)提供科学、技术、工程和数学（STEM）领域的研究和教育机会，强调多样性和包容性；2)社区外展和教育；3)开展研究，深入了解不断变化的世界中热带森林生态系统的未来。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Tropical forests are the most diverse ecosystems in the world with some forests having hundreds of tree species per hectare. The maintenance of this diversity is believed to depend upon complex interactions among species. However, the relationships and interactions among species can be altered by climate change and disturbances such as hurricanes that disrupt resource conditions that govern seedling and sapling interactions in the forest understory. This project will combine a shade house experiment with novel molecular approaches to study how adult trees influence the interactions among seedlings of species on the forest floor beneath their canopies. In addition to disentangling how disturbances and warming may shift the strength and direction of relationships among species, this project thus investigates how plants can control plant-plant interactions by secreting specific molecules from their root tips. These secretions influence which micro-organisms become common and these micro-organisms in turn influence seedling success (either positively by promoting beneficial microbes, or negatively by promoting pathogenic microbes). Specifically, seedlings of canopy trees will be grown in pots at different densities in a shaded greenhouse under a range of growing conditions to simulate global warming and changes in canopy cover (light) that occur with hurricane removal of the adult tree canopy. They will be grown in different combinations of density and with different combinations of the field based micro-organisms that typically associate with the roots of different species of adult trees. The outcome of this work will help us to better predict whether tropical forests will maintain their high level of diversity as the world’s climate continues to change and how changes in light associated with canopy removal during hurricanes or cyclones can change species relationships. In addition to the scientific benefits, this project will offer educational and research opportunities to under-represented students. The study site has an established successful internship program, where recently graduated university students, primarily from Puerto Rico, are provided the opportunity to participate in research. They will be offered the opportunity for internships with the project and gain research experience from it. The team will also collaborate with a non-profit organization in Puerto Rico to coordinate field trips for elementary and middle school students to visit the research site and learn about the project. Overall, this work will contribute to the scientific and broader community understanding of what tropical forests might look like in the future. The maintenance of tropical forest diversity is hypothesized to rely on complex species interactions such as mutualism, predation/pathogen attack, and competition, that regulate seedling dynamics and tree species coexistence. These diversity maintaining processes could be fundamentally altered under projected changes in climate and disturbance regime, yet we have little understanding of how these factors will act independently or in concert to affect biological diversity in tropical forests. This project builds and expands upon an existing infrared warming experiment (Tropical Response to Altered Climate Experiment, TRACE). Based upon preliminary data, the team hypothesizes that the strength and direction of density dependence changes with warming and disturbances because of modifications in species interactions such as associations with mycorrhizal fungi (H1), and that plants can in part control these changes through root exudates (H2). This 2-year project combines a shade house experiment with -omic approaches to evaluate how changes in light, density, microclimate and microbes influence density dependence in different forest species. Specifically, seedlings from tree species will be grown in pots subjected to two soil source treatments (e.g. soil from warming versus control plots at the tRACE site), four microbial treatments (no mycorrhizal fungi, no pathogens, no microbes, control), three densities (low, medium, high), and two light treatments (low and high). Broader impacts of the study will fall into three main foci 1) provide research and educational opportunities in science, technology, engineering and math (STEM) with an emphasis on diversity and inclusion, 2) community outreach and education, and 3) generate research that will provide insight into the future of tropical forested ecosystems in a changing world.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.