Nitrogen influenced competition between the genders of Salix rehderiana.

Male and female willow plants show spatial segregation of genders along the environmental gradients. Skewed gender ratio of willows is not only related to altitude, but also to nutrient status and sexual competition, which can affect their growth and defense by altering secondary metabolite production. The relationship between metabolites and nutrients in the two genders of Salix rehderiana was explored in the Gongga Mountain. We found gender ratio was altered with a change in soil nitrogen (N) status; in the high N habitats, secondary metabolites accumulated in males. Furthermore, pot experiment was conducted to test the effect of nitrogen supply on gender competition in S. rehderiana. Sufficient N supply stimulated females to produce amino acids and carbon-containing secondary metabolites for maintaining their carbon-nitrogen balance, but extra nitrogen for males was used for growth to occupy more space. N supply induced foliar nutrient imbalances and growth of opportunistic species, allowing them to outcompete neighbors. Better carbon allocation and storage in male than female willows would benefit intersexual competitiveness of males if environment N increases. Competition between the genders has a significant correlation with skewed gender ratio, spatial separation and resource utilization. Female willows would suffer fiercer competition for space by males with the increased soil N, which would result in the gender ratio alteration. Therefore, gender ratio of willows is likely to convert to gender balance from female-biased with long-term N deposition in the future.