Global patterns of C 3 /C 4 grass biomass allocation: how aridity mediates nitrogen‐induced divergent strategies
Man Hu, Yujuan Zheng, Hang Shi, Rui He, Jie Gao, Quanfa Zhang, Haishan DangSummary
Plant biomass allocation is dynamically shaped by drought and nitrogen (N) availability, yet how aridity modulates N effects and whether this interplay is conserved across major photosynthetic pathways (C
3
vs C
4
) remain mechanistically unresolved.
Using a global dataset of 2747 root‐to‐shoot ratio (RSR) observations from 631 herbaceous species, we applied a multi‐model framework (Random Forest, linear mixed‐effects models, and Bayesian structural equation modeling) to investigate: how aridity modulates the effect of soil N on the root‐to‐shoot ratio (RSR); and whether this modulatory effect differs between C
3
and C
4
plants.
Increasing aridity promoted a convergent rise in RSR in both C
3
and C
4
grasses. However, soil N directly increased RSR in C
3
plants, but it enhanced net primary productivity in C
4
plants, which indirectly reduced RSR. This decoupling between drought‐response mechanisms and N‐acquisition strategies reveals that while the two functional types followed a shared hydraulic rule, they adhere to distinct N economies.
Our results reveal that increased soil N availability will trigger divergent carbon storage responses in C
3
and C
4
grasslands, potentially exacerbating this functional divergence as atmospheric N deposition continues to rise.