Abstract
AbstractWater deficit in the atmosphere and soil are two key interactive factors that constrain transpiration and vegetation productivity. It is not clear which of these two factors is more important for the water and carbon flux response to drought stress in ecosystems. In this study, field data and numerical modeling were used to isolate their impact on evapotranspiration (ET) and gross primary productivity (GPP) at a tropical forest site in Barro Colorado Island (BCI), Panama, focusing on their response to the drought induced by the El Niño event of 2015–2016. Numerical simulations were performed using a plant hydrodynamic scheme (HYDRO) and a heuristic approach that ignores stomatal sensitivity to leaf water potential in the Energy Exascale Earth System Model (E3SM) Land Model (ELM). The sensitivity of canopy conductance (Gs) to vapor pressure deficit (VPD) obtained from eddy‐covariance fluxes and measured sap flux shows that, at both ecosystem and plant scale, soil water stress is more important in limiting Gs than VPD at BCI during the El Niño event. The model simulations confirmed the importance of water stress limitation on Gs, but overestimated the VPD impact on Gs compared to that estimated from the observations. We also found that the predicted soil moisture is less sensitive to the diversity of plant hydraulic traits than ET and GPP. During the dry season at BCI, seasonal ET, especially soil evaporation at VPD > 0.42 kPa, simulated using HYDRO and ELM, were too strong and will require alternative parameterizations.
Highlights
Tropical forests play a key role in the global carbon cycle by storing atmospheric carbon, reducing the climatic impact of anthropogenic emissions
root-mean-squared error (RMSE) of gross primary productivity (GPP) is 0.77 and 0.93 gC m−2d−1 respectively based on comparisons between the observation and the Energy Exascale Earth System Model Land Model (ELM) simulation and the ensemble mean of hydrodynamic scheme (HYDRO)
Most of the simulations show that there are no differences in ET and GPP caused by model representations during the wet season, but all model results are biased high in ET (0.12–1.03 mm d−1 for the ensemble HYDRO mean) and some are biased high in GPP (0.66–1.54 gC m−2d−1 for the ensemble HYDRO mean) compared to the observations during the dry season
Summary
Tropical forests play a key role in the global carbon cycle by storing atmospheric carbon, reducing the climatic impact of anthropogenic emissions A warmer and drier climate may weaken the ability of tropical forests to mitigate CO2 emissions (Cavaleri et al, 2017; Corlett, 2016). A recent review on the response of tropical rainforests to drought has highlighted the complex mechanisms underlying forest vulnerability to drought (Bonal et al, 2016). The short-term plant response to water stress is to close stomata to regulate water loss (Daszkowska-Golec & Szarejko, 2013) especially at high vapor pressure deficit (VPD)
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