Temperature Thresholds Drive Latitudinal Divergence In Herbaceous Ecosystem Carbon Balance

Shrub–grassland (SGL) ecosystems cover over 40% of Earth’s vegetated land and play a crucial role in regulating the global carbon cycle, yet their large-scale responses to recent warming remain poorly constrained. Here we integrate satellite-derived gross primary productivity (GPP) and fire emissions with top-down estimates of net biosphere production (NBP) from OCO-2 XCO₂ inversions using the GCASv2 assimilation framework to quantify latitudinal trends in SGL net ecosystem production (NEP) from 2015 to 2024.

We find a clear latitudinal divergence in carbon dynamics. NEP has increased in equatorial SGLs but declined in mid-latitude regions. In equatorial areas, persistent increases in GPP surpass modest rises in total ecosystem respiration (TER), resulting in net carbon gains. In contrast, mid-latitude ecosystems experience stronger increases in TER, particularly heterotrophic respiration (Rh), than in GPP as temperatures approach the optimal range for Rh (15–23 °C). This imbalance leads to net carbon losses.

These findings reveal nonlinear, hydrothermal-threshold-driven carbon responses across SGL biomes and emphasize the need to incorporate such temperature–moisture constraints into Earth system models to improve projections of future carbon–climate feedbacks.