Abstract: The allocation patterns of grassland biomass and their regulatory factors in northern China remain poorly understood. We compiled a dataset from literature, integrating 951 independent records on vegetation variables (including aboveground biomass, belowground biomass, root-to-shoot ratio, and species composition), anthropogenic factors (grazing and nitrogen addition), as well as climatic and soil variables. We systematically analyzed the dataset with statistical analysis and machine learning (XGBoost) approaches. The results showed that mean aboveground biomass in northern China grasslands was 191.35±6.97 g·m^-2, belowground biomass was 1461.55±39.11 g·m^-2, and the root-to-shoot ratio was 18.09±0.62. The root-to-shoot ratio exhibited a unimodal pattern with increasing longitude and latitude. Light grazing enhanced biomass, whereas moderate and heavy grazing reduced it. Nitrogen application significantly increased aboveground biomass but decreased belowground biomass. Species composition played a critical role in driving biomass allocation. Grasslands dominated by Poaceae species had higher aboveground biomass but lower belowground biomass and root-to-shoot ratio, whereas those dominated by Asteraceae and Fabaceae species showed higher root-to-shoot ratios. Environmental factors nonlinearly regulated biomass allocation. For instance, belowground biomass first decreased and then increased with increasing mean annual precipitation, while the root-to-shoot ratio initially declined and then rose with increasing mean annual temperature. Our results provide a scientific basis for the sustainable management of grasslands, highlighting the importance of grazing management and nitrogen fertilizer application strategies.

Key words: grassland biomass, grazing intensity, nitrogen addition, species composition