Estimating carbon flux in temperate mixed and broadleaf forests using a simplified approach to estimate nighttime respiration

Carbon sink in forest ecosystems plays an important role in the global carbon cycle, and understanding it is essential for accurate estimation of the carbon balance at global and regional scales (Southern Urals in our case). In this study, we focus on estimating carbon fluxes for mixed and broadleaf forests using both the FLUXNET methodology and a revised algorithm. To validate the algorithm, we collected FLUXNET data from multiple observation sites in mixed and broadleaf forests. We calculated annual mean fluxes of photosynthesis, respiration, and net flux using our algorithm, which calculates the average daily respiration from observations made during daylight hours. The calculations use flux averaging over discrete bins of incoming solar radiation and then extrapolating lineraly a point of zero irradiance. We compared the annual net flux calculations obtained using our approach with those obtained using the FLUXNET methodology, and estimated the correction needed for the annual mean respiration flux based on the results obtained.

Preliminary results show agreement between the net flux calculations using our algorithm and the FLUXNET methodology. At the same time, our algorithm allows for easier quality control via visual inspection of the curve fit for averaged flux data. We compared carbon sinks calculated by inverse modeling across latitudinal zones with estimates from FLUXCOM data and found a larger underestimation of respiration at mid- and low-latitudes, while the discrepancy is less pronounced in the boreal and the Arctic zones. This confirms the value of eddy covariance measurements for estimating net carbon flux in the ecosystems of this zone.