Soil microbes influence nitrogen limit on the plant biomass of the alpine steppe, North Tibet

Abstract

It is uncertain that plant biomass of grassland was co-limited by nitrogen (N) and phosphorus (P) or only limited by N or P. Moreover, it is also unclear why plant biomass was not limited by the P when the N was added at grassland ecosystem. The N and P additional experiment was conducted at the alpine steppe from 2013 to 2017. Results from analyzing response ratio of shoot biomass and leaf N and P concentration to N and P addition suggested that N is the main limiting factor for plant biomass of alpine steppe, and P is synergistic with N in contributing to biomass. Based on the N:P stoichiometry, plants have to increase P absorption due to N addition. Results of SEM analysis showed plant and fungi promoted the activity of phosphatase. At the same time, the abundance of fungi and saprotrophic group associated with decomposition were increased due to N addition, which would provide more P for plant. Those results suggested P deficit of plant due to N addition would be alleviated. Similarly, plant have to increase the N absorption when P was added. Although activity of urease was enhanced by soil microbes and plant, there was a little substrate for microbes because plant biomass was not increased due to P addition. Therefore, composition and function of soil microbes were affected by plant and soil N:P due to N addition, and then delivered P for plant, which will influence the effect of N on plant biomass at alpine steppe.