Data from: Mutualism effectiveness of a fungal endophyte in an annual grass is impaired by ozone

1. Ozone is an increasing tropospheric contaminant of climate change. Exposure to ozone may affect the symbiotic relationship between plants and beneficial microorganisms. In particular, the herbivore resistance mechanism conferred by fungal endophytes (defensive mutualism) may be affected, as any of the ozone-triggered effects (such as elicitation of defence mechanisms against biotrophic fungi or oxidative stress in the apoplastic space) may target the symbiont. 2. Symbiotic and non-symbiotic Lolium multiflorum plants were exposed to ozone for two consecutive days (2 h per day), after which half were infested with 10 aphids (Rhopalosiphum padi). We measured variables related to performance of plants, the endophyte symbiont (alkaloids) and the herbivores. 3. Aphid populations were smaller on symbiotic plants than in non-symbiotic plants in low-ozone conditions. However, this difference disappeared in exposed plants to high-ozone conditions. Under low-ozone conditions, structure of aphid populations on endophyte-symbiotic plants was characterized by a low number of nymphs and a high number of adults. This pattern was not observed with high-ozone exposure. Level of fungal alkaloids (lolines) was not affected by either ozone or herbivory. 4. Results indicate that ozone impairs the grass-endophyte symbiosis without affecting production of alkaloids generally linked with aphids’ response to endophyte presence. Since neither plant biomass nor alkaloid level were affected by ozone, other ozone-mediated mechanisms at molecular or biochemical level may underlie plant-herbivore interaction mediated by fungal endophytes. Thus, the mechanism behind this effect must be determined in future experiments.

1. 臭氧是气候变化驱动下日趋增多的对流层污染物。臭氧暴露可能会影响植物与有益微生物之间的共生关系。其中，由真菌内生菌（fungal endophytes）介导的抗草食动物防御性共生（defensive mutualism）机制或受其影响，因为任何臭氧诱导的效应（例如激活针对活体营养型真菌的防御机制，或质外体空间内的氧化应激）都可能靶向该共生体。2. 本研究将携带共生内生菌与不携带共生内生菌的多花黑麦草（Lolium multiflorum）连续2天暴露于臭氧环境中（每天2小时），随后将半数植株接种10头麦长管蚜（Rhopalosiphum padi）。我们测定了与植株生长表现、内生菌共生体（生物碱）以及草食动物相关的多项指标。3. 在低臭氧环境下，携带内生菌共生体的植株上的蚜虫种群规模小于不携带共生体的植株；但在高臭氧暴露的植株中，这一差异消失。低臭氧环境下，内生菌共生植株上的蚜虫种群结构表现为若虫数量少、成虫数量多，而高臭氧暴露则未呈现该特征。真菌生物碱（黑麦草碱，lolines）的含量不受臭氧暴露或草食动物取食的影响。4. 研究结果表明，臭氧会削弱禾本科植物与内生菌的共生关系，但并未影响通常与蚜虫响应内生菌定植相关的生物碱合成水平。由于植株生物量与生物碱含量均未受臭氧影响，说明在真菌内生菌介导的植物-草食动物互作过程中，臭氧可能通过其他分子或生化层面的调控机制发挥作用。未来实验需明确该效应背后的具体作用机制。