School of Natural Resources and the Environment, University of Arizona, Tucson, Arizona, United States of America.
Arizona-Sonora Desert Museum, Tucson, Arizona, United States of America.
PLoS One. 2019 Oct 31;14(10):e0224417. doi: 10.1371/journal.pone.0224417. eCollection 2019.
Soil-borne fungi influence coexistence of plant species in mesic environments, but much less is known about their effects on demographic processes relevant to coexistence in arid and semi-arid systems. We isolated 43 fungal strains that naturally colonize seeds of an invasive winter annual (Brassica tournefortii) in the Sonoran Desert, and evaluated the impact of 18 of them on seed germination and mortality of B. tournefortii and a co-occurring native annual (Plantago ovata) under simulated summer and winter temperatures. Fungi isolated from B. tournefortii seeds impacted germination and mortality of seeds of both plant species in vitro. Seed responses reflected host-specific effects by fungi, the degree of which differed significantly between the strains, and depended on the temperature. In the winter temperature, ten fungal strains increased or reduced seed germination, but substantial seed mortality due to fungi was not observed. Two strains increased germination of P. ovata more strongly than B. tournefortii. In the summer temperature, fungi induced both substantial seed germination and mortality, with ten strains demonstrating host-specificity. Under natural conditions, host-specific effects of fungi on seed germination may further differentiate plant species niche in germination response, with a potential of promoting coexistence. Both host-specific and non-host-specific effects of fungi on seed loss may induce polarizing effects on plant coexistence depending on the ecological context. The coexistence theory provides a clear framework to interpret these polarizing effects. Moreover, fungi pathogenic to both plant species could induce host-specific germination, which challenges the theoretical assumption of density-independent germination response. These implications from an in vitro study underscore the need to weave theoretical modeling, reductive empirical experiments, and natural observations to illuminate effects of soil-borne fungi on coexistence of annual plant species in variable desert environments.
土壤真菌会影响中生境中植物物种的共存，但对于干旱和半干旱系统中与共存相关的种群过程的影响，人们知之甚少。我们从索诺兰沙漠中一种入侵的冬季一年生植物（ Brassica tournefortii ）的种子中分离出 43 种天然定殖的真菌菌株，并评估了其中 18 种真菌菌株在模拟夏季和冬季温度下对 B. tournefortii 和一种同时存在的本地一年生植物（ Plantago ovata ）的种子萌发和死亡率的影响。从 B. tournefortii 种子中分离出的真菌会影响两种植物种子的离体萌发和死亡率。种子的响应反映了真菌的宿主特异性效应，其程度在菌株间有显著差异，并且取决于温度。在冬季温度下，有 10 种真菌菌株增加或减少了种子的萌发，但没有观察到由于真菌导致的大量种子死亡。有 2 种菌株使 P. ovata 的萌发率增加得比 B. tournefortii 更强。在夏季温度下，真菌诱导了大量的种子萌发和死亡，其中 10 种菌株表现出宿主特异性。在自然条件下，真菌对种子萌发的宿主特异性效应可能会进一步分化植物物种在萌发响应方面的生态位，从而促进共存。真菌对种子损失的宿主特异性和非宿主特异性效应可能会根据生态背景对植物共存产生极化效应。共存理论为解释这些极化效应提供了一个清晰的框架。此外，对两种植物都有致病性的真菌可能会诱导宿主特异性的萌发，这对密度独立萌发响应的理论假设提出了挑战。这些来自体外研究的启示强调需要将理论建模、简化的实证实验和自然观察结合起来，以阐明土壤真菌对变异性沙漠环境中一年生植物物种共存的影响。
