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

这是一个快速反应研究（Rapid）项目，旨在解决飓风玛丽亚和伊尔玛对波多黎各的影响。总体目标是了解飓风等自然干扰如何影响该岛热带森林的植物生物多样性。飓风前后的实验和调查将被用来确定飓风是否破坏了维持那里令人难以置信的植物多样性的过程。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了栖息地，但我们仍然不完全了解这种巨大的多样性是如何维持的，或者人类和自然干扰是如何影响它的。一个著名的假说预测，特定物种的天敌（致病微生物）降低了一些树木的竞争能力，从而使其他树木得以生长和生存，但对这一假说的详细测试很少。该项目将以多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被最近飓风Irma和Maria带来的大量输入和落叶的混合所改变。这些研究将通过位于埃尔云克的卢基洛长期生态研究（LTER）站点的赞助进行。波多黎各和俄勒冈州的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在研究方面的竞争力，以及扩大对科学的参与。Janzen-Connell假说是用来解释热带森林中树木多样性是如何维持的主要假说之一。为了明确验证树木在其周围土壤中具有独特微生物特征的基本假设，将在16公顷的Luquillo森林动态地块（具有人类土地利用梯度）中，对飓风前后9棵目标树底部0-10m处的土壤采样真菌和细菌的DNA进行测序。为了确定Janzen-Connell效应的强度是否被改变，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：飓风强风的混合落叶和碎片的突然输入减弱了冠层树木的微生物特征，由于冠层树木附近的物种特异性病原体负荷被稀释，这削弱了詹森-康奈尔效应；H2：飓风扰动后，由于缺乏落叶树木的光合输入，菌根真菌定植、丰富度和多样性下降，使幼苗更容易受到普遍的病原体攻击和养分限制；H3：近期人类土地利用与飓风扰动相互作用，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，飓风干扰在从加勒比到亚洲热带的大范围热带地区的强度正在增加，本研究的结果将对预测热带森林动态具有普遍意义，并可能为森林恢复研究中观察到的一些无法解释的变化提供见解。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。

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.