Moisture Regulates Contributions of Drought Response Strategy to Interannual Variability in Gross Primary Productivity

The interannual variability (IAV) of terrestrial ecosystem gross primary productivity (GPP) is largely influenced by drought stress, but the importance of plant drought response strategy (drought avoidance and tolerance) to IAV in GPP is still unclear. In this study, we quantified the relative contributions of plant drought-avoidant and -tolerant strategies to IAV in GPP in 5 ecosystems with differential water availability by partitioning the influence of soil water on GPP into 2 processes: (a) influence of soil water status (water content or water potential) on plant water status, which reflects the drought-avoidant strategy, and (b) influence of plant water status on GPP, which reflects the drought-tolerant strategy. The results showed that the 2 plant response strategies are crucial to IAV in GPP, contributing more than 50% in all 5 ecosystems. The relative contribution of drought-avoidant strategy increased while that of drought-tolerant strategy decreased with the increases in soil moisture. A trade-off between drought-avoidant effect and drought-tolerant effect was found in the 2 ecosystems with the highest soil moisture, implying that the GPP may be relatively stable under drought in ecosystems with sufficient water. Overall, our study highlighted the critical role of drought response strategy in regulating the IAV in GPP, which should be further investigated at regional to global scales for accurately predicting IAV in carbon fluxes in a changing climate.