Collaborative Research: Diversity, Distribution, and Demographic Effects of Seed-Associated Fungi in Neotropical Cecropia

真菌病原体日益被认为是热带森林成株和苗木死亡的重要来源，影响着树木的种群、分布和多样性。然而，关于影响种子存活的种子感染真菌的隐藏效应，人们知之甚少。感染种子的真菌可能对树木物种特别重要，这取决于种子在土壤中的存活情况(种子库)是否能成功招募。我们将对三个热带森林(哥斯达黎加、巴拿马、厄瓜多尔)的种子感染真菌(内生菌、腐生植物、病原体)进行详细的生态和分子特征分析，这些真菌与依赖种子库的热带树木(Cecropia、荨麻科)有关。通过田间试验，我们将评估12种植物的种子可归因于真菌的死亡率，以及本地真菌和外来真菌在三种古老森林物种种子存活中的作用。我们将使用分子序列数据来鉴定真菌，并通过重新接种试验来评估感染种子的物种的致病性。在此过程中，我们将检验三个主要假设：(I)不同树种的种子在土壤中的持久性不同，反映出对真菌感染的不同敏感性；(Ii)感染热带种子的真菌种类繁多，并适应当地宿主；(Iii)非致病真菌保护种子免受疾病侵染。该项目有望更深入地了解热带树种多样性和丰富性的潜在因素，这反过来又对森林生态系统的管理和恢复以及维持热带生物多样性产生重要影响。更广泛的影响包括对博士生进行田间生态学和分子技术方面的培训，改善国际层面的合作联系，以及为美国、厄瓜多尔、巴拿马和哥斯达黎加的本科生提供论文支持和培训。我们预计，这项研究将为任何自然系统中种子-真菌相互作用的复杂性提供第一次洞察，并将为热带分子生态学方面的年轻研究人员提供急需的培训。

Fungal pathogens are increasingly recognized as an important source of adult-plant and seedling mortality in tropical forests, influencing tree demography, distributions, and diversity. However, very little is known regarding hidden effects of seed-infecting fungi, which influence seed survival. Seed-infecting fungi are likely to be especially important for tree species depending upon seed survival in soil (seed banks) for successful recruitment. We will undertake a detailed ecological and molecular characterization of seed-infecting fungi (endophytes, saprophytes, pathogens) associated with focal seed-bank-dependent tropical trees (Cecropia, Urticaceae) in three tropical forests (Costa Rica, Panama, Ecuador). Using field experiments, we will assess seed mortality attributable to fungi for 12 species, and the roles of local vs. foreign fungi in seed survival for three old-growth forest species. We will use molecular sequence data to identify fungi, and re-inoculation trials to assess pathogenicity of seed-infecting species. In so doing, we will test three primary hypotheses: (i) seed persistence in soil differs among tree species, reflecting differential susceptibility to fungal infection; (ii) tropical seed-infecting fungi are diverse and adapted to local hosts; (iii) nonpathogenic fungi protect seeds against disease. This project promises a deeper understanding of factors underlying recruitment by a diverse and abundant group of tropical tree species, which in turn has important implications for management and restoration of forest ecosystems and maintenance of tropical biodiversity. Broader impacts include training for a doctoral student in field ecology and molecular techniques, improved collaborative links at an international level, and dissertation support and training for U.S., Ecuadorian, Panamanian and Costa Rican undergraduate students. We anticipate that this study will provide the first insights to the complexity of seed-fungal interactions in any natural system, and will provide much-needed training for young researchers in tropical molecular ecology.