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

真菌病原体越来越被认为是热带森林成虫和幼苗死亡的重要来源，影响树木的人口统计学、分布和多样性。然而，对影响种子存活的侵染真菌的隐藏效应知之甚少。侵染种子的真菌对于树木来说可能是特别重要的，这取决于种子在土壤（种子库）中的存活情况。我们将对三个热带森林（哥斯达黎加、巴拿马、厄瓜多尔）中与依赖种子库的热带树木（Cecropia、荨麻科）相关的侵染种子的真菌（内生菌、腐生菌、病原体）进行详细的生态和分子表征。通过田间试验，我们评估了12种植物的种子因真菌而死亡，以及本地真菌和外来真菌在3种原生林植物种子存活中的作用。我们将使用分子序列数据来鉴定真菌，并进行重新接种试验来评估种子感染物种的致病性。在此过程中，我们将测试三个主要假设：(i)种子在土壤中的持久性因树种而异，反映了对真菌感染的不同敏感性；（ii）热带侵染种子的真菌种类繁多，适应当地寄主；（三）非致病性真菌保护种子免受病害。该项目有望更深入地了解多样化和丰富的热带树种的招募因素，这反过来对森林生态系统的管理和恢复以及热带生物多样性的维持具有重要意义。更广泛的影响包括培训一名野外生态学和分子技术方面的博士生，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。我们期望这项研究将首次揭示任何自然系统中种子-真菌相互作用的复杂性，并将为热带分子生态学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.