Dynamical interactions between plant and oomycete biodiversity in a temperate forest

了解如何维持森林中树木的多样性是一项全球性挑战。虽然侵入性害虫和由病原体引起的新疾病的影响可能是巨大的，但人们对本地害虫和疾病的更微妙的影响知之甚少。例如，本地的病原体和害虫能否通过限制最常见的树种，在森林中为那些本来会被淘汰的稀有物种创造空间，从而促进（而不是破坏）生物多样性？该项目将重点关注原生病原体卵菌在维持太平洋西北地区古老森林树木多样性方面的作用。卵菌或水霉菌是极具破坏性的真菌类植物病原体，最著名的是19世纪50年代导致爱尔兰马铃薯饥荒的原因。虽然众所周知，卵菌是农业病原体，但它们原产于许多森林，并且在许多森林中数量丰富。然而，人们对它们在天然林中的生态作用几乎一无所知。该项目将(i)记录华盛顿州南部风河老森林中存在的卵菌物种，（ii）确定每种卵菌攻击或限制森林中不同类型树种的能力，以及（iii）使用现代遗传技术探索卵菌如何适应不同类型的树种。通过整合所有这些信息，研究人员将更好地了解卵菌和其他病原体在森林中的作用。这种认识将改善对自然生态系统及其中发生的疾病的管理。该项目还将培养本科生、研究生和博士后。利用培养和非培养方法对植物和卵菌进行初步普查，并对植物和卵菌进行基因分型，将导致植物接种实验，从而确定卵菌的寄主范围。基因组和转录组测序将研究宿主范围狭窄的卵菌如何适应优势寄主植物物种的遗传多样性的机制，并将更深入地研究宿主范围广泛的卵菌如何适应其栖息地中植物物种的多样性。一个特别的重点将是地方性的宽宿主范围卵菌的作用，以及它们与优势和非优势宿主物种的相互作用可能不同。通过整合风河遗址的卵菌和植物的分类、遗传、基因组和功能信息，将测试关于卵菌在影响植物生物多样性方面可能发挥作用的两种广泛假设。这两种假设是：(A)寄主范围狭窄和寄主范围广泛的病原体可能降低优势寄主的适合度，从而促进植物物种和遗传多样性。(B)优势宿主可能受益于广泛宿主范围病原体的存在，因为它们对广泛宿主范围病原体具有更强的抵抗力或耐受性。(A)和(B)可以对不同种类甚至菌株的病原体独立起作用。

Understanding how the diversity of trees in forests is maintained is a global challenge. While the impact of invasive pests and new diseases caused by pathogens can be dramatic, the more subtle impacts of native pests and diseases are poorly understood. For example, can native pathogens and pests help promote (rather than destroy) biodiversity by limiting the most common tree species, creating room in the forest for rare species that would otherwise be outcompeted? This project will focus on the role of native pathogens, called oomycetes, in maintaining tree diversity in an old growth forest in the Pacific Northwest. Oomycetes, or water molds, are highly destructive fungus-like plant pathogens, best known for causing the Irish potato famine in the 1850s. Though well known as agricultural pathogens, oomycetes are native to and abundant in many forests. However, almost nothing is known about their ecological roles in natural forests. This project will (i) document the oomycete species present in the Wind River old growth forest in southern Washington state, (ii) determine the ability of each oomycete species to attack or limit different types of tree species in the forest, and (iii) use modern genetic techniques to explore how oomycetes may adapt to different types of tree species. By integrating all this information, the researchers will develop a better understanding of the roles of oomycetes and other pathogens in forests. This understanding will improve management of natural ecosystems and the diseases that occur within them. The project will also train undergraduate, graduate and postdoctoral students.An initial census of plants and oomycetes, using both culturing and culture-independent methods, together with genotyping of the plants and oomycetes, will lead to plant-inoculation experiments that will identify the host ranges of the oomycetes. Genome and transcriptome sequencing will examine the mechanisms by which narrow host range oomycetes may adapt to genetic diversity in the dominant host plant species, and will examine more deeply how broad host range oomycetes may adapt to a diversity of plant species in their habitat. A particular focus will be on the role of endemic broad-host-range oomycetes, and how their interactions with dominant and non-dominant host species may differ. By integrating taxonomic, genetic, genomic and functional information about the oomycetes and plants at the Wind River site, two broad hypotheses regarding possible roles of oomycetes in influencing plant biodiversity will be tested. The two hypotheses are: (A) Narrow and broad host range pathogens may reduce the fitness of dominant hosts and so promote plant species and genetic diversity. (B) Dominant hosts may benefit from the presence of broad host range pathogens due to superior resistance or tolerance to broad-host-range pathogens. Both (A) and (B) may operate independently for different species, or even strains, of pathogens.