Plant-microbe interactions regulate the aboveground community nitrogen accumulation rate in different environmental conditions on the Tibetan Plateau

Experimental studies have well illustrated that plant and microbe interactions play an important role in the absorption of nitrogen (N) under different environmental conditions. However, it remains to be seen what role plant-microbe interactions play in regulating plant N accumulation rates (NAR) over broad climatic and geographic scales. Here, a transect survey was conducted in alpine grassland on the Tibetan Plateau to measure aboveground net primary production and plant N concentration corresponding with phenology indexes, the NAR patterns were measured by changepoint analysis. Meanwhile, matrix correlation analysis and variation partitioning analysis were performed to explore the dynamic of NAR in response to environment factors. Finally, structural equation model was employed to express the path coefficients of environmental factors on NAR. A significantly (P<0.05) lower NAR (8.9 mg/m(2)/day) in cold-dry climates than that in warm-wet climates (31.1 mg/m(2)/day) were detected. Our results further demonstrated a cooperative interaction between microbes and plants stimulated NAR in weakly resource-limited environments but a competitive effect of microbes on plants-constrained NAR in strongly resource-limited environments. The NAR was strongly governed by coupled water-heat availability and microbial biomass via their effects on plant diversity. Our findings highlighted that plant-microbe interactions offered an important framework to better understand the generalizable mechanisms of plant N accumulation in different environmental conditions. The knowledge of ecological N accumulation mechanisms obtained here not only emphasized the importance of incorporating plant phenology and dynamics of plant N into the ecological N cycle model but also promoted our understanding of resource utilization between plants and soil microbes under ongoing global climate change.

Automated summary

Experimental studies have shown that plant-microbe interactions are crucial for nitrogen absorption in different environments, with lower NAR in cold-dry climates and higher NAR in warm-wet climates. Cooperative interactions between microbes and plants stimulate NAR in weakly resource-limited environments, while competitive effects of microbes constrain NAR in strongly resource-limited environments. The NAR is influenced by water-heat availability and microbial biomass, which in turn affect plant diversity.