Figure 5 The relationship between stability of plot biomass and logarithm (with base 10) of N-addition rate were given in two samples, all sample plots and (b) loop samples with intransitive structure. The solid circle represented coordinates of plot biomass average and\(\log_{10}N\), and the solid line represented the standard deviation.
With the increase of nitrogen enrichment, the biomass stability decreased and the state of grassland ecosystem became worser and worser comparing with natural state (in Fig. 5a,), because environmental filtering reordered the species dominance. When N = 1 g N·m-2·year-1, it was conducive to enhance biomass stability, but N ≥ 2 g N·m-2·year-1 is the opposite.
Fig. 5b given the biomass stability in intransitive competitive structure changes with logarithm of N-addition rates. It was found that the stability performed an increasing trend and then decreasing. Intransitive structure completely offset the negative effect of medium N-addition rates (5, 10 g N·m-2·year-1) on the stabilities. But excessive nitrogen enrichments (15, 20, and 50 g N·m-2·year-1) completely covered the ecological action of intransitive competition, resulting in the level of the three stabilities similar to that of the all samples.