Institute of Grassland Science, Key Laboratory of Vegetation Ecology, Ministry of Education/Jilin Songnen Grassland Ecosystem National Observation and Research Station, Northeast Normal University, Changchun, 130024, China.
Rocky Mountain Research Station, USDA Forest Service, 800 E. Beckwith Avenue, Missoula, MT, 59801, USA.
New Phytol. 2023 Jul;239(1):340-349. doi: 10.1111/nph.18912. Epub 2023 Apr 13.
Parasites can catalyze or inhibit interactions between their hosts and other species, but the ecosystem-level effects of such interaction modifications are poorly understood. We conducted a large-scale field experiment in temperate grasslands of China to understand how foliar fungal pathogens influenced top-down effects of cattle on plant diversity and productivity. When foliar pathogens were suppressed, cattle grazing strongly reduced biomass of the dominant grass, Leymus chinensis, generating competitive release that significantly increased community-level species richness and evenness. In the absence of grazing, pathogen attack on L. chinensis had no measurable effect on host biomass. However, pathogens disrupted top-down effects of herbivory by inhibiting grazing effects on plant biomass and species richness. Mechanistically, fungal pathogens were linked to increased alkaloid and reduced nitrogen levels in leaf tissue, which appeared to deter cattle grazing on L. chinensis. In conclusion, foliar pathogens can suppress top-down effects of large herbivores on grassland community composition and ecosystem function by modifying the strength of their host's interactions with dominant consumers. Parasites may act as modulators of ecosystem function when their direct effects on host abundance are overshadowed by powerful influences on host traits that modify their interactions with competitors, herbivores, or predators.
寄生虫可以催化或抑制其宿主与其他物种之间的相互作用，但人们对这种相互作用改变的生态系统水平效应知之甚少。我们在中国温带草原进行了一项大规模的野外实验，以了解叶部真菌病原体如何影响牛对植物多样性和生产力的自上而下的影响。当叶部病原体受到抑制时，牛的放牧强烈降低了优势草种羊草的生物量，产生了竞争释放，显著增加了群落水平的物种丰富度和均匀度。在没有放牧的情况下，病原体对羊草的攻击对宿主生物量没有可衡量的影响。然而，病原体通过抑制放牧对植物生物量和物种丰富度的影响，破坏了食草动物的自上而下的作用。从机制上讲，真菌病原体与叶片组织中生物碱含量的增加和氮含量的降低有关，这似乎阻止了牛吃草。总之，叶部病原体可以通过改变其与主要消费者的相互作用强度来抑制大型食草动物对草原群落组成和生态系统功能的自上而下的影响。当寄生虫对宿主丰度的直接影响被其对宿主特征的强大影响所掩盖时，这些影响会改变宿主与竞争者、食草动物或捕食者的相互作用，寄生虫可能成为生态系统功能的调节者。
