Nitrogen-influenced competition between the genders of Salix rehderiana.

Male and female willow plants show spatial segregation of genders along the environmental gradients. The skewed gender ratio of willows is related not only 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 that the gender ratio was altered with a change in soil nitrogen (N) status; in the high N habitats, secondary metabolites accumulated in males. Furthermore, a pot experiment was conducted to test the effect of N supply on gender competition in S. rehderiana. Sufficient N supply stimulated females to produce amino acids and carbon (C)-containing secondary metabolites for maintaining their C-N balance, but extra N for males was used for growth to occupy more space. Nitrogen supply induced foliar nutrient imbalances and growth of opportunistic species, allowing them to outcompete neighbors. Better C 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.

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