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

[摘要] The precipitation legacy effect, defined as the impact of historicalprecipitation (PPT) on extant ecosystem dynamics, has been recognized as animportant driver in shaping the temporal variability of dryland abovegroundnet primary production (ANPP) and soil respiration. How the PPT legacyinfluences whole ecosystem-level carbon (C) fluxes has rarely beenquantitatively assessed, particularly at longer temporal scales. Weparameterized a process-based ecosystem model to a semiarid savannaecosystem in the southwestern USA, calibrated and evaluated the model performancebased on 7 years of eddy-covariance measurements, and conducted two sets ofsimulation experiments to assess interdecadal and interannual PPT legacyeffects over a 30-year simulation period. The results showed that decreasingthe previous period/year PPT (dry legacy) always increased subsequent netecosystem production (NEP) whereas increasing the previous period/year PPT(wet legacy) decreased NEP. The simulated dry-legacy impacts mostlyincreased subsequent gross ecosystem production (GEP) and reduced ecosystemrespiration (R_e), but the wet legacy mostly reduced GEP and increasedR_e. Although the direction and magnitude of GEP and R_e responsesto the simulated dry and wet legacies were influenced by both the previousand current PPT conditions, the NEP responses were predominantly determinedby the previous PPT characteristics including rainfall amount, seasonalityand event size distribution. Larger PPT difference between periods/yearsresulted in larger legacy impacts, with dry legacies fostering more Csequestration and wet legacies more C release. The carryover of soil Nbetween periods/years was mainly responsible for the GEP responses, while thecarryovers of plant biomass, litter and soil organic matter were mainlyresponsible for the R_e responses. These simulation results suggest thatprevious PPT conditions can exert substantial legacy impacts on currentecosystem C balance, which should be taken into account while assessing theresponse of dryland ecosystem C dynamics to future PPT regime changes.

[学科分类] 地球化学与岩石