Nitrogen enhancement amplifies the precipitation-driven productivity allocation pattern in temperate and alpine grasslands.

Grasslands constitute critical carbon sinks, vulnerable to altered precipitation and nitrogen deposition. While hyphae mediate ecosystem carbon allocation pathways, their role remains poorly quantified. We conducted multi-site manipulative experiments across China's temperate and alpine grasslands, quantifying carbon allocation to aboveground biomass, roots, and hyphae under precipitation change and nitrogen (N) enhancement. Our findings showed that along the precipitation gradient increasing, proportional carbon allocation to aboveground productivity (f_ANPP) increased, while allocations to root (f_BNPP) and hyphal (f_HNPP) productivity decreased. Moreover, productivity allocation in alpine grasslands was 1.30-1.50-fold more sensitive to precipitation changes than in temperate grasslands. N enhancement did not alter the precipitation-driven allocation pattern but amplified its sensitivity by 1.18∼-3.25-fold. And community traits, soil and root traits play an important mediating role in regulating productivity allocation through precipitation and nitrogen addition. These findings highlight the differential changes in the productivity allocation of different components driven by global change factors and emphasize the indispensable role of hyphae in regulating the stability of carbon sinks.