Restored legume acts as a “nurse” to facilitate plant compensatory growth and biomass production in mown grasslands

Anthropogenic disturbances have led to substantial declines in grassland legumes worldwide, with consequences for plant nutritional quality, biodiversity, food-web complexity, and ecosystem sustainability. Despite the growing acknowledgment of the significance of legume presence, it has rarely been investigated how the introduction of legumes affects the growth of neighboring plants over time and the underlying mechanisms that influence biomass production during grassland utilization. To address these gaps, we established legume-restored grasslands followed by 7 years of mowing (once a year) and phosphorus (P) application to simulate defoliation management and improve legume performance. We observed significant higher compensatory growth rate and aboveground biomass in legume-restored grasslands compared to naturally restored grasslands. These improvements can be attributed to the combined effect of an increase in legume proportion in plant communities and the improved performance of neighboring plant species after legume restoration (nursing effect). This nursing effect further increased the relative importance of the mass ratio effect in explaining the improved biomass in legume-restored grasslands after mowing. Moreover, the compensatory growth rate in naturally restored grasslands decreased significantly over time, while the compensatory growth rate in legume-restored grasslands tended to increase, indicating higher sustainable biomass production in legume-restored grasslands. P application increased aboveground biomass, but did not alter plant community structure, regardless of whether legumes were used to restore grasslands. Here, we show for the first time that legume introduction can sustainably provide higher biomass production through enhancing compensatory growth in natural grasslands that have suffered from prolonged or intense defoliation. This highlights the critical role of leguminous species in a long-term grassland restoration.