Department of Ecology, Evolution and Behavior, University of Minnesota, Saint Paul, MN, 55108, USA.
Kellogg Biological Station, Michigan State University, Hickory Corners, MI, 49060, USA.
Am J Bot. 2019 Aug;106(8):1081-1089. doi: 10.1002/ajb2.1340. Epub 2019 Aug 6.
Microbial symbionts can buffer plant hosts from environmental change. Therefore, understanding how global change factors alter the associations between hosts and their microbial symbionts may improve predictions of future changes in host population dynamics and microbial diversity. Here, we investigated how one global change factor, precipitation, affected the maintenance or loss of symbiotic fungal endophytes in a C grass host. Specifically, we examined the distinct responses of Epichloë (vertically transmitted and systemic) and non-epichloid endophytes (typically horizontally transmitted and localized) by considering (1) how precipitation altered associations with Epichloë and non-epichloid endophytic taxa across host ontogeny, and (2) interactive effects of water availability and Epichloë on early seedling life history stages.
We manipulated the presence of Epichloë amarillans in American beachgrass (Ammophila breviligulata) in a multiyear field experiment that imposed three precipitation regimes (ambient or ±30% rainfall). In laboratory assays, we investigated the interactive effects of water availability and Epichloë on seed viability and germination.
Reduced precipitation decreased the incidence of Epichloë in leaves in the final sampling period, but had no effect on associations with non-epichloid taxa. Epichloë reduced the incidence of non-epichloid endophytes, including systemic p-endophytes, in seeds. Laboratory assays suggested that association with Epichloë is likely maintained, in part, due to increased seed viability and germination regardless of water availability.
Our study empirically demonstrates several pathways for plant symbionts to be lost or maintained across host ontogeny and suggests that reductions in precipitation can drive the loss of a plant's microbial symbionts.
微生物共生体可以缓冲植物宿主免受环境变化的影响。因此，了解全球变化因素如何改变宿主与其微生物共生体之间的联系，可能会提高对宿主种群动态和微生物多样性未来变化的预测。在这里，我们研究了一种全球变化因素——降水，如何影响 C 草宿主共生真菌内生菌的维持或丧失。具体来说，我们通过考虑（1）降水如何改变宿主个体发育过程中与内生性 Epichloë 和非内生性内生菌属的联系，以及（2）水分供应和内生性 Epichloë 对早期幼苗生活史阶段的相互作用，来研究 Epichloë（垂直传播和系统性）和非 Epichloid 内生菌（通常是水平传播和局部性）的不同反应。
我们在一个多年野外实验中操纵美国海滨草（Ammophila breviligulata）中 Epichloë amarillans 的存在，该实验采用了三种降水制度（环境或±30%降雨）。在实验室实验中，我们研究了水分供应和内生性 Epichloë 对种子活力和发芽的相互作用。
减少降水会降低最后一次采样期叶片中内生性 Epichloë 的发生率，但对非内生性分类群的联系没有影响。内生性 Epichloë 降低了非内生性内生菌的发生率，包括系统性 p-内生菌，在种子中。实验室实验表明，由于种子活力和发芽率的增加，无论水分供应情况如何，内生性 Epichloë 的联系可能会得以维持。
我们的研究经验性地证明了植物共生体在宿主个体发育过程中丧失或维持的几种途径，并表明降水减少可能导致植物微生物共生体的丧失。
