The alpine meadow of the Qinghai–Tibetan Plateau is an essential terrestrial ecosystem that provides a livelihood for approximately 9.8 million local inhabitants and serves as a habitat for millions of livestock. Changing facets of the global environment, such as increased nitrogen deposition, have not only affected the abundance and quality of forgeable plants but have also increased the prevalence and severity of plant diseases caused by pathogens. However, whether or not and to what extent these pathogens affect the rangeland quality of the alpine meadow remains unclear. We conducted a factorial experiment with the exclusion of fungal and oomycete pathogens to investigate the impact of various pathogens on rangeland quality in an alpine meadow in the Qinghai–Tibetan Plateau. We measured forage production for each plant species, forage quality (including measurements of organic matter, crude protein, phosphorus, total phenolics, neutral detergent fiber (NDF), metabolizable energy, and digestibility) for 11 abundant species, and community composition. We found that fungal pathogen exclusion and the combination of fungal and oomycete pathogen exclusion primarily affected nutrient production by altering forage production rather than changing community composition or forage quality. Exclusion of both fungal and oomycete pathogens led to a significant increase in community forage production, although no significant effect was observed for individual exclusion of fungal or oomycete pathogens. Excluding either fungal pathogens alone or simultaneous exclusion of both fungal and oomycete pathogens significantly increased the metabolizable energy content of the community. In contrast, oomycete pathogen exclusion significantly decreased the forage metabolizable energy content of the community. The exclusion of both fungal and oomycete pathogens also considerably increased the yield of organic matter, total phenolics, NDF, digestible dry matter, and metabolizable energy. However, the direction and magnitude of the effect of fungal and oomycete pathogen exclusion varied widely across the different species studied. These results suggest that the interaction of fungal and oomycete pathogens constitutes an essential limiting factor in rangeland quality that has not been previously recognized. Greater attention should be placed on overall forage production rather than forage quality in the context of grassland pathogen control strategies. Furthermore, metabolizable energy content may serve as an effective indicator for predicting the impact of pathogenic activity on forage quality.

青藏高原高山草甸是重要的陆地生态系统，为当地约980万居民提供生计，也是数百万牲畜的栖息地。全球环境的变化，例如氮沉降的增加，不仅影响了可伪造植物的丰度和质量，而且还增加了病原体引起的植物病害的流行和严重程度。然而，这些病原体是否以及在多大程度上影响高寒草甸的牧场质量仍不清楚。我们进行了排除真菌和卵菌病原体的析因实验，研究了各种病原体对青藏高原高寒草甸牧场质量的影响。我们测量了每种植物物种的饲料产量、11 个丰富物种的饲料质量（包括有机质、粗蛋白、磷、总酚、中性洗涤纤维 (NDF)、代谢能和消化率的测量）以及群落组成。我们发现，真菌病原体排除以及真菌和卵菌病原体排除的组合主要通过改变草料产量而不是改变群落组成或草料质量来影响养分生产。排除真菌和卵菌病原体导致社区草料产量显着增加，尽管单独排除真菌或卵菌病原体没有观察到显着效果。单独排除真菌病原体或同时排除真菌和卵菌病原体显着增加了群落的代谢能含量。相反，卵菌病原体排除显着降低了群落的饲料代谢能含量。排除真菌和卵菌病原体也大大增加了有机物、总酚、NDF、可消化干物质和可代谢能的产量。然而，在所研究的不同物种中，真菌和卵菌病原体排除效果的方向和程度差异很大。这些结果表明，真菌和卵菌病原体的相互作用构成了牧场质量的一个重要限制因素，这一点此前尚未被认识到。在草原病原体控制策略中，应更多地关注整体饲料生产而不是饲料质量。此外，代谢能含量可以作为预测病原体活动对饲料质量影响的有效指标。