Effects of coexisting species differences on plant carbon and nitrogen contents in micropatches of legumes and nonlegumes

A micropatch is not only an important indicator of the degree of grassland degradation but also the main information base for implementing grassland management strategies. The effects of interspecific relationships on the plant carbon and nitrogen contents in micropatches in nitrogen-limited ecosystems remains to be studied. In an experimental system, we measured the carbon and nitrogen contents of the whole plant on single-species and two-species micropatches. To investigate whether the diversity of coexisting species causes differences in the biological nitrogen fixation of legumes, we also measured the atom%¹⁵N of whole plants. The results showed the following: 1) The interspecific difference in total carbon (TC) content (F = 8.121, P < 0.01), total nitrogen (TN) content ( F = 45.001, P < 0.01), and atom% ¹⁵N (F = 6.460, P < 0.01) of the legumes was extremely significant. The coexistence with nonlegume species had no effect on the TC content ( F = 0.708, P > 0.05), TN content ( F = 0.131, P > 0.05), or atom% ¹⁵N (F = 0.271, P > 0.05) of the legumes. 2) The differences in the TC content ( F = 6.883, P < 0.01), TN content ( F = 9.791, P < 0.01), and atom% ¹⁵N (F = 5.067, P < 0.01) among the nonlegumes were extremely significant. The response of nonleguminous TN to the coexistence with legumes was species-specific ( F = 3.840, P < 0.05). 3) The TC content, TN content, and atom% ¹⁵N of the legumes on the two-species micropatches were not significantly different compared with those of the single-species micropatches (P > 0.05); the atom% ¹⁵N of the nonlegumes was significantly lower (P < 0.01), and the TN content of nonlegumes was significantly higher ( P < 0.01). The TC content, TN content, and atom% ¹⁵N of legumes were relatively stable and not affected by the coexisting species. After coexisting with leguminous plants in two-species micropatches, the TN content of the nonleguminous plants significantly increased. We speculate that the nitrogen fixation ability of the legumes mainly depended on their taxonomic identity and was unrelated to their coexistence with nonlegumes. Nonleguminous plants in two-species micropatches will benefit from nitrogen transfer; the effect of species coexistence on the carbon and nitrogen contents of the whole plant in a micropatch is species-specific.