Interpopulation Variation in Reproductive Strategies of Leymus chinensis Along Geographical Gradients in Northeast China: From Phenotypic Patterns to Adaptive Mechanisms

Geographic variation in plant functional traits plays a pivotal role in elucidating plant adaptive strategies, typically driven by both macro-climatic gradients and local-scale environmental heterogeneity. However, for clonal plants, the role of reproductive allocation in shaping offspring fitness across geographic scales remains poorly understood. We investigated 30 Leymus chinensis populations in Northeast China in July 2021 and 2022 to examine geographic variation in growth, reproductive traits, and germination characteristics. The results revealed that: 1) most growth and reproductive traits exhibited significant interpopulation variation but lacked broad-scale geographic patterns, with the exception of ramet density (RD), which followed a longitude-influenced clumped distribution. This suggests that trait differentiation is primarily driven by local environmental heterogeneity rather than macro-climatic gradients. Sexual reproductive output (e.g., heading rate and seed number) displayed high variability (Coefficient of variation (CV) = 0.71–0.87), whereas thousand seed weight (TSW) was highly conservative (CV = 0.09). 2) No global trade-off was observed between seed number (SN) and TSW; however, a context-dependent trade-off emerged in low-biomass populations, where TSW correlated positively with heading plant height (HPH) and negatively with reproductive allocation (SHR). 3) Multivariate regression analysis indicated that the germination rate (GER) was significantly influenced by HPH (negative effect) and SN (positive effect), while mean germination time (MGT) was driven by aboveground biomass and flower number per spike. Notably, maternal reproductive allocation and fecundity (HPH and SN), rather than seed size (TSW), were the primary predictors of offspring fitness (GER). These findings suggest that Leymus chinensis optimizes offspring establishment through flexible resource allocation strategies. In conclusion, local habitat heterogeneity is the main driver of trait differentiation in Leymus chinensis populations, and maternal physiological ‘pre-conditioning’ via resource partitioning outweighs seed size in determining reproductive success.