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能会被气候变化和飓风等干扰所改变，这些干扰破坏了支配森林林下树苗和树苗相互作用的资源条件。这个项目将结合树荫实验和新的分子方法来研究成年树木如何影响树冠下森林地面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之间关系的强度和方向之外，这个项目还因此调查了植物如何通过从根尖分泌特定的分子来控制植物与植物的相互作用。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苗木的成功(要么通过促进有益微生物而积极地影响，要么通过促进病原微生物而消极地影响)。具体地说，树冠树苗将在一系列生长条件下以不同密度种植在有阴影的温室中，以模拟全球变暖和随着飓风移动成年树冠而发生的树冠覆盖(光)的变化。它们将在不同的密度组合中种植，并与田间微生物的不同组合一起种植，这些微生物通常与不同种类的成年树木的根相关。这项工作的结果将有助于我们更好地预测，随着世界气候的持续变化，热带森林是否会保持其高度的多样性，以及飓风或气旋期间与树冠移除相关的光照变化如何改变物种关系。除了科学上的好处，这个项目还将为未被充分代表的学生提供教育和研究机会。该研究网站建立了一个成功的实习计划，为刚毕业的大学生提供参与研究的机会，这些大学生主要来自波多黎各。他们将获得与该项目实习的机会，并从中获得研究经验。该团队还将与波多黎各的一个非营利性组织合作，协调中小学生参观研究现场并了解该项目的实地考察。总体而言，这项工作将有助于科学和更广泛的社区了解热带雨林未来可能是什么样子。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、捕食/病原体攻击和竞争，这些相互作用调节苗木动态和树种共存。这些维持多样性的过程可能会在气候和干扰机制的预期变化下发生根本改变，但我们对这些因素将如何独立或协同作用影响热带森林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(热带对气候变化的反应实验，TRACE)。这个为期两年的项目结合了荫棚实验和基因组方法，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。

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.