Influence of Interactions between Nitrogen, Phosphorus Supply and Epichloe bromicola on Growth of Wild Barley (Hordeum brevisubulatum)

Epichloe endophytes are biotrophic fungi that establish mutualistic symbiotic relationship with grasses and affect performance of the host under different environments. Wild barley (Hordeum brevisubulatum) is an important forage grass and often infected by Epichloe bromicola, thus showing tolerances to stresses. Since the plant growth correlates with both microbial infection and nutrient stoichiometry, this study was performed to investigate whether the function of Epichloe bromicola endophyte to improve host growth depend upon the nitrogen (N), phosphorus (P) fertilization. Epichloe-infected (E+) and Epichloe-free (E-) wild barley plants were subjected to nine types of mixed N (0.2 mM, 3 mM, 15 mM) and P (0.01 mM, 0.1 mM, 1.5 mM) levels treatments for 90 d to collect plant samples and determine multiple related indexes. We found that E. bromicola and N, P additions positively affected seed germination. Further, E. bromicola significantly enhanced chlorophyll content and root metabolic activity under N-deficiency, and meanwhile, might alter allocation of photosynthate under different conditions. The contents of N, P and stoichiometry of C:N:P of E+ plants were significantly higher than that of E- under nutrient deficiency, but contrary results were observed under adequate nutrients. Therefore, we propose that the growth-promoting ability of E. bromicola is closely correlated with N and P additional levels. Under low N, P additions, positive roles of endophyte are significant as opposed to negative roles under high N, P additions.