Foliar fungal endophytes are ubiquitous plant symbionts that can affect plant growth and reproduction via their roles in pathogen and stress tolerance, as well as plant hormonal signaling. Despite their importance, we have a limited understanding of how foliar fungal endophytes respond to varying environmental conditions such as nutrient inputs. The responses of foliar fungal endophyte communities to increased nutrient deposition may be mediated by the simultaneous effects on within-host competition as well as the indirect impacts of altered host population size, plant productivity, and plant community diversity and composition. Here, we leveraged a 7-year experiment manipulating nitrogen, phosphorus, potassium, and micronutrients to investigate how nutrient-induced changes to plant diversity, plant productivity, and plant community composition relate to changes in foliar fungal endophyte diversity and richness in a focal native grass host, Andropogon gerardii. We found limited evidence of direct effects of nutrients on endophyte diversity. Instead, the effects of nutrients on endophyte diversity appeared to be mediated by accumulation of plant litter and plant diversity loss. Specifically, nitrogen addition is associated with a 40% decrease in plant diversity and an 11% decrease in endophyte richness. Although nitrogen, phosphorus, and potassium addition increased aboveground live biomass and decreased relative Andropogon cover, endophyte diversity did not covary with live plant biomass or Andropogon cover. Our results suggest that fungal endophyte diversity within this focal host is determined in part by the diversity of the surrounding plant community and its potential impact on immigrant propagules and dispersal dynamics. Our results suggest that elemental nutrients reduce endophyte diversity indirectly via impacts on the local plant community, not direct response to nutrient addition. Thus, the effects of global change drivers, such as nutrient deposition, on characteristics of host populations and the diversity of their local communities are important for predicting the response of symbiont communities in a changing global environment.

中文翻译：

---

植物多样性和凋落物积累介导了营养添加后叶面内生真菌丰富度的丧失

叶面真菌内生菌是普遍存在的植物共生体，可通过其在病原体和胁迫耐受性以及植物激素信号传导中的作用影响植物生长和繁殖。尽管它们很重要，但我们对叶内真菌如何对不同的环境条件（如营养输入）做出反应的了解有限。叶面真菌内生菌群落对养分沉积增加的反应可能由对寄主内竞争的同时影响以及寄主种群大小、植物生产力和植物群落多样性和组成改变的间接影响介导。在这里，我们利用一项为期 7 年的操纵氮、磷、钾和微量营养素的实验来研究养分引起的植物多样性、植物生产力、和植物群落组成与焦点原生草宿主 Andropogon gerardii 的叶内真菌多样性和丰富度的变化有关。我们发现营养素对内生菌多样性的直接影响的证据有限。相反，养分对内生菌多样性的影响似乎是由植物凋落物的积累和植物多样性的丧失所介导的。具体而言，氮添加与植物多样性减少 40% 和内生菌丰富度减少 11% 相关。尽管氮、磷和钾的添加增加了地上活生物量并减少了相对的穿心莲盖度，但内生菌多样性与活植物生物量或穿心莲盖度没有共变。我们的研究结果表明，该焦点宿主内的真菌内生菌多样性部分取决于周围植物群落的多样性及其对移民繁殖体和扩散动态的潜在影响。我们的研究结果表明，元素养分通过对当地植物群落的影响间接降低内生菌多样性，而不是对养分添加的直接反应。因此，全球变化驱动因素（如养分沉积）对寄主种群特征及其当地群落多样性的影响对于预测共生群落在不断变化的全球环境中的反应很重要。对营养添加没有直接反应。因此，全球变化驱动因素（如养分沉积）对寄主种群特征及其当地群落多样性的影响对于预测共生群落在不断变化的全球环境中的反应很重要。对营养添加没有直接反应。因此，全球变化驱动因素（如养分沉积）对寄主种群特征及其当地群落多样性的影响对于预测共生群落在不断变化的全球环境中的反应很重要。