Precipitation legacy effects on dryland ecosystem carbon fluxes: direction, magnitude and biogeochemical carryovers

Authors: SHEN, W. - Chinese Academy Of Sciences; JENERETTE, G.D. - University Of California; HUI, D. - Tennessee State University; Scott, Russell - Russ

Submitted to: Biogeosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2016
Publication Date: 1/21/2016
Citation: Shen, W., Jenerette, G., Hui, D., Scott, R.L. 2016. Precipitation legacy effects on dryland ecosystem carbon fluxes: direction, magnitude and biogeochemical carryovers Biogeosciences. 13:425-439. https://doi.org/10.5194/bg-13-425-2016.
DOI: https://doi.org/10.5194/bg-13-425-2016

Interpretive Summary: The legacy of past precipitation patterns has been recognized as an important factor in shaping the way plants respond to current precipitation. However, the precipitation legacy effects on total ecosystem carbon fluxes of which plants uptake of carbon by photosynthesis is only a part has rarely been quantitatively assessed. We adjusted an ecosystem-level water and carbon cycling simulation model to match observations made at a semiarid mesquite savanna ecosystem in southwestern United States and conducted simulation experiments to assess the PPT legacy effects. We found that total ecosystem uptake of carbon increased when the past precipitation legacy was dry and decreased when the past legacy was wet. In general, the dry legacy effect was due to a more vigorous plant response which was stimulated by increased soil nitrogen, and the wet legacy effect was due to the stimulation of soil respiration (carbon loss) due to the increase in carbon substrate for microbes. These results suggest that precipitation-induced biogeochemical carryovers can impose substantial legacy impacts on ecosystem carbon balance that should be taken into account when predicting the response of carbon fluxes to current and future climate.

Technical Abstract: The precipitation legacy effect, defined as the impact of historical precipitation (PPT) on extant ecosystem dynamics, has been recognized as an important driver in shaping the temporal variability of dryland aboveground net primary production (ANPP) and soil respiration. How the PPT legacy influences whole ecosystem-level carbon (C) fluxes has rarely been quantitatively assessed, particularly at longer temporal scales. We parameterized a process-based ecosystem model to a semiarid savanna ecosystem in the southwestern USA, calibrated and evaluated the model performance based on 7 years of eddy-covariance measurements, and conducted two sets of simulation experiments to assess interdecadal and interannual PPT legacy effects over a 30-year simulation period. The results showed that decreasing the previous period/year PPT (dry legacy) always increased subsequent net ecosystem production (NEP) whereas increasing the previous period/year PPT (wet legacy) decreased NEP. The simulated dry-legacy impacts mostly increased subsequent gross ecosystem production (GEP) and reduced ecosystem respiration (Re/, but the wet legacy mostly reduced GEP and increased Re. Although the direction and magnitude of GEP and Re responses to the simulated dry and wet legacies were influenced by both the previous and current PPT conditions, the NEP responses were predominantly determined by the previous PPT characteristics including rainfall amount, seasonality and event size distribution. Larger PPT difference between periods/years resulted in larger legacy impacts, with dry legacies fostering more C sequestration and wet legacies more C release. The carryover of soil N between periods/years was mainly responsible for the GEP responses, while the carryovers of plant biomass, litter and soil organic matter were mainly responsible for the Re responses. These simulation results suggest that previous PPT conditions can exert substantial legacy impacts on current ecosystem C balance, which should be taken into account while assessing the response of dryland ecosystem C dynamics to future PPT regime changes.