Respiratory carbon losses and the carbon-use efficiency of a northern hardwood forest, 1999-2003

Abstract

• 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 (R∑) of soil (Rs), leaf (Rl) and wood (Rw) respiration, and meteorologically by measuring above-canopy nocturnal CO2 fluxes (Fcn). • Here we estimated R∑ over 5 yr in a forest in Michigan, USA, and compared R∑ and Fcn on turbulent nights. We also evaluated forest carbon-use efficiency (Ec = P NP/PGP) using biometric estimates of net primary production (PNP) and R∑ and Fcn-derived estimates of gross primary production (PGP). • Interannual variation in R∑ was modest (142 g C m-2 yr-1). Mean annual R∑ was 1425 g C m-2 yr-1; 71% from Rs, 18% from Rl, and 11% from Rw. Hourly R∑ was well correlated with Fcn, but 11 to 58% greater depending on the time of year. Greater R∑ 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 R∑ 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. © New Phytologist (2005).