Essene Adam L, Shek Katherine L, Lewis J D, Peay Kabir G, McGuire Krista L
Department of Biological Sciences, Fordham University, New York City, NY, United States.
Department of Biology, Institute of Ecology and Evolution, University of Oregon, Eugene, OR, United States.
Front Plant Sci. 2017 Oct 27;8:1828. doi: 10.3389/fpls.2017.01828. eCollection 2017.
The role that mycorrhizal fungal associations play in the assembly of long-lived tree communities is poorly understood, especially in tropical forests, which have the highest tree diversity of any ecosystem. The lowland tropical rain forests of Southeast Asia are characterized by high levels of species richness within the family Dipterocarpaceae, the entirety of which has been shown to form obligate ectomycorrhizal (ECM) fungal associations. Differences in ECM assembly between co-occurring species of dipterocarp have been suggested, but never tested in adult trees, as a mechanism for maintaining the coexistence of closely related tree species in this family. Testing this hypothesis has proven difficult because the assembly of both dipterocarps and their ECM associates co-varies with the same edaphic variables. In this study, we used high-throughput DNA sequencing of soils and Sanger sequencing of root tips to evaluate how ECM fungi were structured within and across a clay-sand soil nutrient ecotone in a mixed-dipterocarp rain forest in Malaysian Borneo. We compared assembly patterns of ECM fungi in bulk soil to ECM root tips collected from three ecologically distinct species of dipterocarp. This design allowed us to test whether ECM fungi are more strongly structured by soil type or host specificity. As with previous studies of ECM fungi on this plot, we observed that clay vs. sand soil type strongly structured both the bulk soil and root tip ECM fungal communities. However, we also observed significantly different ECM communities associated with two of the three dipterocarp species evaluated on this plot. These results suggest that ECM fungal assembly on these species is shaped by a combination of biotic and abiotic factors, and that the soil edaphic niche occupied by different dipterocarp species may be mediated by distinct ECM fungal assemblages.
菌根真菌共生关系在长寿树木群落组装过程中所起的作用，目前还知之甚少，尤其是在热带森林中，热带森林拥有任何生态系统中最高的树木多样性。东南亚的低地热带雨林以龙脑香科内部的高物种丰富度为特征，该科所有物种都已被证明会形成专性外生菌根（ECM）真菌共生关系。有研究提出了龙脑香科共生物种之间外生菌根组装的差异，但从未在成年树木中进行过测试，以此作为维持该科密切相关树种共存的一种机制。检验这一假设已被证明很困难，因为龙脑香科植物及其外生菌根共生体的组装都与相同的土壤变量共同变化。在本研究中，我们利用土壤的高通量DNA测序和根尖的桑格测序，来评估在马来西亚婆罗洲的一个混合龙脑香雨林中，外生菌根真菌在粘土 - 砂土养分交错带内和交错带之间是如何构建的。我们将大量土壤中外生菌根真菌的组装模式与从三种生态上不同的龙脑香科树种收集的外生菌根根尖进行了比较。这种设计使我们能够测试外生菌根真菌是受土壤类型还是宿主特异性的影响更大。与之前在该地块上对外生菌根真菌的研究一样，我们观察到粘土与砂土类型强烈地构建了大量土壤和根尖外生菌根真菌群落。然而，我们还观察到，在该地块上评估的三种龙脑香科树种中的两种，其相关的外生菌根群落存在显著差异。这些结果表明，这些树种上的外生菌根真菌组装是由生物和非生物因素共同塑造的，并且不同龙脑香科树种所占据的土壤生态位可能由不同的外生菌根真菌组合介导。
