Decunta Facundo A, Pérez Luis I, Malinowski Dariusz P, Molina-Montenegro Marco A, Gundel Pedro E
Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA), Facultad de Agronomía, Buenos Aires, Argentina.
Texas A&M AgriLife Research, Vernon, TX, United States.
Front Plant Sci. 2021 Mar 24;12:644731. doi: 10.3389/fpls.2021.644731. eCollection 2021.
Symptomless fungal endophytes in the genus are repeatedly mentioned to increase tolerance of cool-season grasses to a wide range of environmental stress factors, mainly drought. However, the generality of this idea is challenged because (i) most studies have been conducted on two economically important forage grasses {tall fescue [ (Schreb.) Dumort] and perennial ryegrass ( L.)}, (ii) endophyte-mediated mechanisms and effects on plant responses to drought have shown to be highly variable across species, and that (iii) symbiosis incidence in plant populations occurring in extremely arid environments is usually low. We question this idea by reviewing the existing information about fungal endophyte effects on drought tolerance in cool-season grasses. We combined standard review, vote counting, and calculation of effect sizes to synthesize the literature, identify information gaps, and guide future research. The total number of studies was higher for domesticated than for wild species, a ratio that was balanced when papers with data quality for effect size calculus were considered. After the drought, endophyte-infected plants accumulated more aboveground and belowground biomass than non-infected counterparts, while no effect on tillering was observed. However, these effects remained significant for wild (even on tillering) but not for domesticated species. Interestingly, despite the continuous effort in determining physiological mechanisms behind the endophyte effects, no studies evaluated plant fecundity as a measure of ecological fitness nor vital rates (such as survival) as to escalate individual-level variables to population. Together with the high variability in results, our work shows that generalizing a positive effect of fungal endophytes in plant tolerance to drought may be misleading. Future studies combining field surveys with manipulative experiments would allow us to unravel the role of fungal endophytes in plant adaptation by considering the evolutionary history of species and populations to the different ecological contexts.
属无症状真菌内生菌被反复提及可提高冷季型草对多种环境胁迫因素（主要是干旱）的耐受性。然而，这一观点的普遍性受到了挑战，原因如下：（i）大多数研究是在两种具有经济重要性的饲草上进行的{高羊茅[（Schreb.）Dumort]和多年生黑麦草（L.）}，（ii）内生菌介导的机制及其对植物干旱响应的影响在不同物种间表现出高度变异性，并且（iii）在极端干旱环境中植物种群的共生发生率通常较低。我们通过回顾关于真菌内生菌对冷季型草耐旱性影响的现有信息来质疑这一观点。我们结合标准综述、投票计数和效应量计算来综合文献、识别信息空白并指导未来研究。驯化物种的研究总数高于野生物种，在考虑具有效应量计算数据质量的论文时，这一比例达到平衡。干旱后，感染内生菌的植物地上和地下生物量积累比未感染的对应植物更多，而对分蘖未观察到影响。然而，这些影响在野生植物中仍然显著（甚至对分蘖也有影响），但在驯化物种中则不然。有趣的是，尽管一直在努力确定内生菌效应背后的生理机制，但没有研究将植物繁殖力作为生态适应性的衡量指标，也没有将生命率（如存活率）作为将个体水平变量提升到种群水平的指标。连同结果的高度变异性，我们的研究表明，将真菌内生菌对植物耐旱性的积极影响一概而论可能会产生误导。未来结合实地调查与操纵实验的研究将使我们能够通过考虑物种和种群对不同生态环境的进化历史，来阐明真菌内生菌在植物适应中的作用。
