RAPID: Microbial signatures of tropical trees across human land use gradients before and after hurricane disturbance: implications for the disruption of coexistence mechanisms

这是一个快速响应研究 (RAPID) 项目，旨在解决波多黎各飓风玛丽亚和艾尔玛的影响。 总体目标是了解飓风等自然干扰如何影响岛上热带森林的植物生物多样性。飓风前后的实验和调查将用于确定飓风是否破坏了被认为负责维持当地植物生命令人难以置信的多样性的过程。热带雨林是地球上最多样化的生态系统之一，为一半以上的动植物物种提供栖息地，但我们仍然不完全了解如何维持如此巨大的多样性，也不完全了解人类和自然干扰如何影响它。一个众所周知的假设预测，物种特异性的天敌（致病微生物）会降低某些树木的竞争能力，从而使其他树木能够生长和生存，但这一假设的详细测试很少。该项目将以各种方式检验这一假设，通过检查树木和土壤微生物的分布模式是否彼此同步，以及这种相互作用是否因最近飓风“艾尔玛”和“玛丽亚”的大量输入和落叶混合物而改变。 这些研究将在云盖卢基洛长期生态研究 (LTER) 站点的支持下进行。波多黎各和俄勒冈州学生和研究人员的智力和技术能力建设将直接有利于提高美国研究竞争力以及扩大科学参与的目标。詹森-康奈尔假说是解释如何维持热带森林树木多样性的主要假设之一。为了明确测试树木在其周围土壤中具有独特微生物特征的基本假设，将对飓风前后 16 公顷卢基洛森林动态图中 9 棵目标树根部 0-10 m 处采样的土壤中的真菌和细菌 DNA 进行测序，该区域具有人类土地利用梯度。为了确定詹森-康奈尔效应的强度是否改变，以及土地利用遗产如何与这些过程相互作用，将进行幼苗移植实验，并分离病原体和菌根真菌并用于进一步的实验。结合该团队广泛的飓风前数据，将测试以下假设： H1：飓风强风中混合落叶和碎片的突然输入减弱了树冠树的微生物特征，由于树冠树附近物种特异性病原体负载被稀释，从而削弱了 Janzen-Connell 效应； H2：飓风干扰后，由于缺乏落叶树木的光合作用输入，菌根真菌的定殖、丰富度和多样性下降，使幼苗更容易受到普遍病原体的攻击和营养限制； H3：近期人类土地利用与飓风干扰相互作用，进一步阻碍微生物介导的共存过程。 由于人类干扰在所有热带森林中普遍存在，而且从加勒比海到亚洲热带地区，飓风扰动的强度在大范围热带地区不断增加，因此这项研究的结果将对预测热带森林动态产生普遍影响，并可能提供对森林恢复研究中观察到的一些无法解释的变化的深入了解。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

This is a Rapid Response Research (RAPID) project to address the impacts of Hurricanes Maria and Irma in Puerto Rico. The overall goal is to understand how natural disturbances such as hurricanes impact plant biodiversity in tropical forests on the Island. Experiments and surveys before and after the hurricanes will be used to determine whether or not the hurricanes disrupted the process thought to be responsible for maintaining the incredible diversity of plant life there. Tropical rain forests are one of the most diverse ecosystems on Earth, and provide habitats for more than half of all plant and animal species, but we still do not fully understand how such immense diversity is maintained or how human and natural disturbances affect it. One well-known hypothesis predicts that species-specific natural enemies (disease-causing microbes) reduce the competitive ability of some trees, thereby allowing other trees to grow and survive, but detailed tests of this hypothesis are few. This project will test the hypothesis in various ways, by examining whether tree and soil microorganism distribution patterns are in sync with one another, and whether such interactions were altered by massive inputs and mixtures of leaf litter from recent hurricanes Irma and Maria. The studies will take place through the auspices of the Luquillo Long-term Ecological Research (LTER) site in El Yunque. The intellectual and technical capacity building for students and researchers in Puerto Rico and Oregon will directly benefit goals of improving the competitiveness of the United States in research, as well a broadening participation in science.The Janzen-Connell hypothesis is one of the main hypotheses evoked to explain how tree diversity in tropical forests is maintained. To explicitly test the underlying assumption that trees have unique microbial signatures in the soils surrounding them, the DNA of fungi and bacteria will be sequenced from soils sampled at 0-10m within the bases of nine target trees before and after the hurricane in the 16-ha Luquillo Forest Dynamics Plot, which has a gradient of human land use. To determine whether or not the strength of Janzen-Connell effects was altered, and how land use legacies interact with these processes, seedling transplant experiments will be conducted, and pathogens and mycorrhizal fungi will be isolated and used for further experiments. In combination with this team's extensive pre-hurricane data, the following hypotheses will be tested: H1: Sudden inputs of mixed leaf litter and debris from hurricane-force winds attenuate microbial signatures of canopy trees, which weakens Janzen-Connell effects due to diluted species-specific pathogen loads near canopy trees; H2: Mycorrhizal fungal colonization, richness, and diversity decrease following hurricane disturbance due to a lack of photosynthetic input from defoliated trees, making seedlings more vulnerable to generalized pathogen attack and nutrient limitation; H3: Recent human land use interacts with hurricane disturbance to further impede microbially-mediated coexistence processes. Since human disturbance is pervasive in all tropical forests, and hurricane disturbance is increasing in intensity across a wide range of tropical areas from the Caribbean to the Asian tropics, results of this study will have generalizable implications for predicting tropical forest dynamics, and may provide insight into some of the unexplained variation observed in studies of forest recovery.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.