Foliar fungal pathogen inhibition increases ecosystem carbon sequestration independently of nitrogen enrichment in a Tibetan alpine meadow

Anthropogenically caused nitrogen (N) enrichment may stimulate both photosynthetic carbon (C) fixation and infection of foliar pathogens. However, the interactive effects of N input and foliar fungal pathogens on the ecosystem C cycling are poorly understood. Using a 6-year field experiment with N input and fungicide application in a Tibetan alpine meadow, we examined how N enrichment and foliar fungal pathogens influence ecosystem C sequestration independently and in combination, possibly resulting in interactions between N enrichment and fungal pathogens. Nitrogen input increased the gross ecosystem productivity (GEP) and ecosystem respiration (ER) through increasing plant biomass and foliar N content, but did not affect net ecosystem productivity (NEP). Fungicide application increased GEP and NEP by relieving foliar pathogen infection but did not affect ER, resulting in net increased ecosystem C sequestration. However, no significant interactive effects between N input and fungicide application were detected.

Synthesis. These results indicate that foliar fungal pathogens are critical biotic factors influencing ecosystem C sequestration in alpine ecosystems, independent of N input. This study emphasizes the important role of biotic factors in regulating ecosystem functions.