Abstract: In traditional mangrove forest management, the purification benefits of mangrove species were pursued unilaterally, but the concomitant effects of exogenous pollution on soil microbial interface were ignored. To examine the effects of N addition on C and N stoichiometry and homeostasis characteristics of plants soil microbes in the mangrove system, I carried out a greenhouse experiment using an automatic tidal-simulation device with five levels of N addition (0, 5, 10, 20, and 30 g N·m^-2·a^-1) and two sets of simulation systems, with and without mangrove plants. The results showed that medium and low N additions were beneficial to soil microbial biomass C and N, while high N addition inhibited soil microbial biomass. Nitrogen addition did not affect C and N stoichiometry of Kandelia obovata (P>0.05), but had significant effects on soil C content, microbial biomass C, microbial biomass N and microbial biomass C∶N (P<0.01). The presence of mangrove plants promoted soil microbial activity, and increased microbial biomass N by 11%-45%. There was a strong coupling relationship between soil nutrients, Kandelia obovata roots, and soil microorganisms. The stoichiometric homeostasis of C and N in aboveground biomass of plants showed absolutely steady state under N addition. Soil microbial biomass C, N, and root C∶N were sensitive to the changes of soil nutrients. With increasing N addition level, soil C∶N ratio decreased. The increased N addition level will accelerate the decomposition of soil organic matter, leading to higher soil carbon emission.

Key words: nitrogen addition, soil, microorganism, ecological stoichiometry, homeostasis.