Krishnadas Meghna, Comita Liza S
School of Forestry and Environmental Studies, Yale University, 195 Prospect Street, New Haven, CT, 06511, USA.
Smithsonian Tropical Research Institute, Box 0843-03092, Balboa, Ancón, Panama.
Oecologia. 2018 Jan;186(1):259-268. doi: 10.1007/s00442-017-4006-1. Epub 2017 Nov 13.
Soil fungi are key mediators of negative density-dependent mortality in seeds and seedlings, and the ability to withstand pathogens in the shaded understory of closed-canopy forests could reinforce light gradient partitioning by tree species. For four species of tropical rainforest trees-two shade-tolerant and two shade-intolerant-we conducted a field experiment to examine the interactive effects of fungal pathogens, light, and seed density on germination and early seedling establishment. In a fully factorial design, seeds were sown into 1 m plots containing soil collected from underneath conspecific adult trees, with plots assigned to forest edge (high light) or shaded understory, high or low density, and fungicide or no fungicide application. We monitored total seed germination and final seedling survival over 15 weeks. Shade-intolerant species were strongly constrained by light; their seedlings survived only at the edge. Fungicide application significantly improved seedling emergence and/or survival for three of the four focal species. There were no significant interactions between fungicide and seed density, suggesting that pathogen spread with increased aggregation of seeds and seedlings did not contribute to pathogen-mediated mortality. Two species experienced significant edge-fungicide interactions, but fungicide effects in edge vs. interior forest varied with species and recruitment stage. Our results suggest that changes to plant-pathogen interactions could affect plant recruitment in human-impacted forests subject to fragmentation and edge-effects.
土壤真菌是种子和幼苗中负密度依赖死亡率的关键调节因子，而在封闭树冠森林的阴暗林下抵御病原体的能力可能会加强树种对光照梯度的划分。对于四种热带雨林树木——两种耐荫树种和两种不耐荫树种——我们进行了一项田间试验，以研究真菌病原体、光照和种子密度对种子萌发和幼苗早期建立的交互作用。在完全析因设计中，将种子播种到1米见方的地块中，这些地块含有从同种成年树下采集的土壤，地块被分配到森林边缘（高光）或阴暗林下、高密度或低密度，以及施用或不施用杀菌剂的处理。我们在15周内监测了种子的总萌发率和最终的幼苗存活率。不耐荫树种受到光照的强烈限制；它们的幼苗仅在边缘存活。施用杀菌剂显著提高了四种重点树种中三种的幼苗出土率和/或存活率。杀菌剂与种子密度之间没有显著的交互作用，这表明随着种子和幼苗聚集增加而传播的病原体并没有导致病原体介导的死亡率。有两个树种经历了显著的边缘 - 杀菌剂交互作用，但边缘和森林内部的杀菌剂效果因树种和幼苗招募阶段而异。我们的结果表明，植物 - 病原体相互作用的变化可能会影响受破碎化和边缘效应影响的人为干扰森林中的植物招募。
