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Keywords:

  • carbon cycle;
  • ecosystem;
  • eddy covariance;
  • gross primary productivity (GPP);
  • leaf;
  • respiration;
  • soil;
  • wood

Summary

  • • 
    Quantitative assessment of carbon (C) storage by forests requires an understanding of climatic controls over respiratory C loss. Ecosystem respiration can be estimated biometrically as the sum (RΣ) of soil (Rs), leaf (Rl) and wood (Rw) respiration, and meteorologically by measuring above-canopy nocturnal CO2 fluxes (Fcn).
  • • 
    Here we estimated RΣ over 5 yr in a forest in Michigan, USA, and compared RΣ and Fcn on turbulent nights. We also evaluated forest carbon-use efficiency (Ec = PNP/PGP) using biometric estimates of net primary production (PNP) and RΣ and Fcn-derived estimates of gross primary production (PGP).
  • • 
    Interannual variation in RΣ was modest (142 g C m−2 yr−1). Mean annual RΣ was 1425 g C m−2 yr−1; 71% from Rs, 18% from Rl, and 11% from Rw. Hourly RΣ was well correlated with Fcn, but 11 to 58% greater depending on the time of year. Greater RΣ compared with Fcn resulted in higher estimated annual PGP and lower annual Ec (0.42 vs 0.54) using biometric and meteorological data, respectively.
  • • 
    Our results provide one of the first multiyear estimates of RΣ in a forested ecosystem, and document the responses of component respiratory C losses to major climatic drivers. They also provide the first assessment of Ec in a deciduous forest using independent estimates of PGP.