The growth respiration component in eddy CO₂ flux from a Quercus ilex mediterranean forest

Ecosystem respiration, arising from soil decomposition as well as from plant maintenance and growth, has been shown to be the most important component of carbon exchange in most terrestrial ecosystems. The goal of this study was to estimate the growth component of whole-ecosystem respiration in a Mediterranean evergreen oak Quercus ilex) forest over the course of 3 years. Ecosystem respiration (R^eco) was determined from night-time carbon dioxide flux (F_c) using eddy correlation when friction velocity (u_*) was greater than 0.35 m s^-1 We postulated that growth respiration could be evaluated as a residual after removing modeled base R^eco from whole-ecosystem R^eco during periods when growth was most likely occurring. We observed that the model deviated from the night-time F_c-based R^eco during the period from early February to early July with the largest discrepancies occurring at the end of May, coinciding with budburst when active aboveground growth and radial growth increment are greatest. The highest growth respiration rates were observed in 2001 with daily fluxes reaching up to 4g Cm^-2. The cumulative growth respiration for the entire growth period gave total carbon losses of 170, 208, and 142 g Cm^-2 for 1999, 2001, and 2002, respectively. Biochemical analysis of soluble carbohydrates, starch, cellulose, hemicellulose, proteins, lignin, and lipids for leaves and stems allowed calculation of the total construction costs of the different growth components, which yielded values of 154, 200, and 150 g C for 3 years, respectively, corresponding well to estimated growth respiration. Estimates of both leaf and stem growth showed very large interannual variation, although average growth respiration coefficients and average yield of growth processes were fairly constant over the 3 years and close to literature values. The time course of the growth respiration may be explained by the growth pattern of leaves and stems and by cambial activity. This approach has potential applications for interpreting the effects of climate variation, disturbances, and management practices on growth and ecosystem respiration.