Collaborative Research: Testing a microbial-association-distribution hypothesis to explain spatial distributions and species co-existence in a community of epiphytic plants

几乎所有的野生植物都依靠有益的真菌，也就是菌根真菌来获得足够的营养。植物和真菌之间的这种关系可能有助于解决生物多样性研究中的一个关键难题，即如此多的植物物种如何能够竞争相同的水、光和土壤养分资源，而又在相同的自然群落中共存。该项目将在哥斯达黎加的一片高度多样化的热带森林中进行实验，以测试：1)不同的植物物种是否与不同的真菌相关；2)只有在存在适合该物种的有益真菌的情况下，才会出现物种；3)与不同的真菌相关，减少植物物种之间的竞争，促进共存。这项研究将重点放在生长在森林树干和树枝上的丰富的兰花上，因为已经知道这些物种与菌根真菌形成了密切的联系。成果将促进对维持自然多样性的机制的了解，该项目将向公众和科学界传播研究结果，以促进保护热带森林的多样性。该项目还将培训本科生和研究生以及博士后研究人员，包括科学界代表性不足的群体成员，并促进国际科学合作。提出的植物-真菌联合如何塑造兰花群落及其生态位结构的概念模型是，真菌本身是植物利用的资源，也是植物获得水和养分等资源的手段，从而决定植物的空间分布和物种共存。这一假设将通过两项综合研究来解决，这两项研究将(1)对热带森林中的兰花、真菌和环境变量进行首次空间采样，以及(2)通过在有和没有合适真菌的位置放置种子包来实验确定兰花种子的建立是否受到真菌分布的限制。这两项研究都将使用下一代测序方法来识别环境中的真菌，并将包括对兰花和真菌的生态位和相互作用网络的新的统计分析。研究结果将显示：(1)真菌呈片状分布，(2)兰花的真菌群丛不同，(3)兰花幼苗的建立和成虫分布受到真菌分布的限制，(4)共生兰花物种在利用真菌和它们的伴生真菌吸取资源的基质中表现出生态位分配。

Nearly all wild plants depend upon beneficial fungi, called mycorrhizal fungi, to obtain adequate nutrition. This relationship between plants and fungi may help solve a key puzzle in the study of biodiversity, how so many species of plants can compete for the same resources of water, light, and soil nutrients and yet co-exist in the same natural community. This project will conduct experiments in a highly diverse tropical forest in Costa Rica to test if: 1) different plant species associate with different fungi; 2) species only occur where the appropriate beneficial fungi for that species are present; and 3) association with different fungi reduces competition between plant species and promotes co-existence. The research will focus on the rich array of orchids that grow on the trunks and branches in the forest, since it is already known that these species form close associations with mycorrhizal fungi. Results will advance understanding of the mechanisms that maintain natural diversity, and the project will disseminate findings to the public as well as to the scientific community to promote conservation of the diversity in tropical forests. The project will also train undergraduate and graduate students and postdoctoral researchers, including members of groups under-represented in science, and promote international scientific collaboration. The proposed conceptual model for how plant-fungal associations could shape orchid communities and their niche structures is that fungi are themselves resources exploited by the plants, as well as the means by which plants acquire resources such as water and nutrients, and thus determine plant spatial distributions and species coexistence. This hypothesis will be addressed through two integrated studies that will (1) conduct the first such spatial sampling of orchids, fungi, and environmental variables in a tropical forest and (2) experimentally determine whether orchid seed establishment is limited by the distribution of fungi by placing seed packets in locations with and without suitable fungi. Both studies will employ next-generation sequencing methods to identify fungi in the environment and will include novel statistical analyses of the niches and interaction networks of orchids and fungi. Findings will show whether (1) fungi are patchily distributed, (2) orchids differ in their fungal associations, (3) orchid seedling establishment and adult distributions are limited by fungal distributions, and (4) co-occurring orchid species show niche partitioning in their use of fungi and in the substrates from which their associated fungi draw resources.