Estimating transpiration and the sensitivity of carbon uptake to water availability in a subalpine forest using a simple ecosystem process model informed by measured net CO2 and H2O fluxes

摘要: Modeling how the role of forests in carbon cycle will respond to predicted changes water availability hinges on an understanding processes controlling use ecosystems. Recent studies forest ecosystem modeling have employed data-assimilation techniques generate parameter sets that conform observations, and predict net CO2 exchange (NEE) its component processes. Since cycles are linked, there should be additional process information available from H2O exchange. We coupled SIPNET (Simple Photosynthesis EvapoTranspiration), a simplified model function, with system estimate parameters leading predictions most closely matching fluxes measured by eddy covariance high-elevation, subalpine ecosystem. When optimized using measurements exchange, matched observed NEE (RMSE = 0.49 g C m−2) but underestimated transpiration calculated independently sap flow factor 4. Consequently, carbon-only optimization was insensitive imposed availability. Including flux data both reduced fit only slightly (RME = 0.53 g C m−2), however this parameterization also reproduced independent (r2 = 0.67, slope = 0.6). A significant amount can extracted simultaneous analysis which improved accuracy estimates evapotranspiration. Conversely, failure include streams results mask responses cycling variation precipitation. In applying conditioned at Niwot Ridge AmeriFlux site, we onset is coincident warm soil temperatures. However, after snow has covered ground fall, inter-annual variability fraction evapotranspiration composed transpiration; dominated years when late fall air temperatures were high enough maintain photosynthesis, sublimation surface snowpack colder photosynthetic activity had ceased. Data-assimilation used quantify response uptake where linked.