Temperature-dependent variations in under-canopy herbaceous foliar diseases following shrub encroachment in grasslands

Abstract The spread of woody plants into grasslands represents a worldwide concern because of its impact on species biodiversity and ecosystem operations. However, our comprehension of the influence of shrubs on herbaceous diseases in grasslands is limited. In our study, we performed extensive examinations on herbaceous populations under the shrub canopy as well as nearby grassland patches in shrubby grasslands over 4,000 kilometers. This large-scale assessment encompassed grassland regions with significant variability in both temperature and precipitation. Our findings uncovered that shrubs elevated the under-canopy pathogen load of herbaceous foliar fungal diseases by increasing the air humidity of the herbaceous assemblages alongside aboveground biomass in warmer regions. However, in colder regions, shrub expansion reduced both pathogen load and herbaceous biomass below the canopy. Temperature, rather than precipitation, was the primary driver for the variations in biomass and herbaceous pathogen load in the variable under-canopy herbaceous populations. These contrasting alterations in herbaceous biomass and diseases following shrub expansion, along with the related environmental variations, emphasize the requirement for adaptive management approaches tailored to shrub encroachment scenarios.