Aims

Leaf-associated microbiome is an essential component of ecosystems. Enhanced deposition of atmosphere nitrogen (N) has profound impacts on grassland ecosystems. However, little is known about the effects of N enrichment on leaf-associated bacterial (LAB) communities of grassland ecosystems.

Methods

Based on a 19-yr field N-addition experiment in a temperate steppe, we examined the effects of N addition on LAB communities in 6 dominant species belonging to the two functional groups of grasses and forbs by measuring bacterial diversity, functional groups, network complexity and assembly process in the LAB communities, and leaf morphological and physiological traits of these grasses and forbs.

Results

N addition increased LAB α diversity approximately threefold in grasses but decreased it by 28.6% in forbs. N addition enhanced LAB network complexity in grasses, while suppressing it in forbs. Bacterial β diversity in grasses was more sensitive to N addition than in forbs. The assemblage of bacterial community in grasses and forbs was mainly steered by regulating functional taxa via changing leaf soluble sugars and leaf structure. Beneficial symbiotic microbes in grasses including N-fixing and phototrophy bacteria were stimulated by N addition, while N addition suppressed the bacterial functional groups of nitrite/nitrate ammonification involved in N cycle in forbs. LAB community assembly was simultaneously driven by the deterministic and stochastic processes, underscoring its inherent complexity. underscores the complexity of the process.

Conclusions

These findings highlight multiple effects of N enrichment on biodiversity and functioning of grassland ecosystems ranging from plants and soil to leaf-associated microbiome.