Species turnover and intraspecific trait variation jointly mediate the responses of the above- and belowground biomass stability to nutrient enrichment and precipitation change in a desert grassland

1. It is known that artificial nutrient enrichment and precipitation changes reduce biomass stability, but how they regulate the impact of plant biomass stability through plant functional component assembly remains poorly understood.2. In a 7-year desert grassland experimental site under nutrient addition (nitrogen, phosphorus, and potassium) and precipitation change (±50%), we quantified how plant functional component assembly regulates the stability of aboveground, belowground, and total biomass through species groups. We measured three aspects of plant trait structure: species turnover, intraspecific trait variation, and conservative and acquisition strategies of the leaf economic spectrum.3. Both nutrient addition and reduced precipitation decreased the stability of aboveground, belowground, and total biomass. Increased precipitation enhanced the stability of aboveground biomass, while the interaction between nutrient addition and increased precipitation elevated the stability of belowground and total biomass. The total biomass stability was determined by the stability of belowground biomass in the 0-20 cm soil layer.4. Precipitation change and nutrient enrichment influenced biomass stability through different trait-assembly pathways, with precipitation acting mainly via species turnover and nutrient enrichment via intraspecific trait variation. However, these assembly responses did not necessarily stabilize biomass stability.