Abstract: The plasticity of both sexual reproduction and clonal growth is crucial for the adaptation of clonal plant populations, with trade-offs often observed between these two ecological processes. Vegetative ramets are essential for clonal growth, yet their role in regulating the plasticity of sexual reproduction, especially under nitrogen (N) enrichment, remains poorly understood. A series of field and pot experiments were conducted to test how vegetative ramets affect the plasticity in sexual reproduction within a clonal fragment (units of reproductive ramet with different number of vegetative ramets), in perennial Leymus chinensis under N application. Results showed that the densities of both vegetative and total ramets exhibited a significant increase in response to rising N concentrations. Throughout all N concentrations in situ, L. chinensis population predominantly consisted of independent reproductive ramets that were not physically connected to vegetative ramets. Furthermore, N application increased the proportion of reproductive ramets that connected with a greater number of vegetative ramets. Independent reproductive ramets exhibited generally the poorest sexual reproductive characteristics across all N concentrations. Resource translocation between ramets was bidirectional with net translocation preferentially flowing toward vegetative ramets during the milk-ripe stage. N application produced only a limited enhancement of sexual reproductive traits. Our study provides the first comprehensive explanation for the poor sexual reproduction of L. chinensis from the perspectives of clonal fragment types and the nutrient supply mechanisms underlying its predominantly vegetative propagation strategy. We further elucidate the underlying factors contributing to the poor sexual reproduction performance but high plasticity via nutrient translocation among ramets in situ.

Key words: clonal fragment, 15N and 13C bidirectional tracers, perennial grass, plasticity, physiological integration, sexual reproduction