Respiratory costs of producing and maintaining stem biomass in eight co-occurring tree species

Given the importance of carbon allocation for plant performance and fitness, it is expected that competition and abiotic stress influence respiratory costs associated with stem wood biomass production and maintenance. In this study, stem respiration (R) was measured together with stem diameter increment in adult trees of eight co-occurring species in a sub-Mediterranean forest stand for 2 years. We estimated growth R (R-g), maintenance R (R-m) and the growth respiration coefficient (GRC) using two gas exchange methods: (i) estimating R-g as the product of growth and GRC (then R-m as R minus R-g) and (ii) estimating R-m from temperature-dependent kinetics of basal R-m at the dormant season (then R-g as R minus R-m). In both cases, stem basal-area growth rates governed intra-annual variation in R, R-g and R-m. Maximum annual R-m occurred slightly before or after maximum R-g. The mean contribution of R-m to R during the growing season ranged from 56% to 88% across species using method 1 and from 23% to 66% using method 2. An analysis accounting for the phylogenetic distance among species indicated that more shade-tolerant, faster growing species exhibited higher R-m and R-g than less shade-tolerant, slower growing ones, suggesting a balance between carbon supply and demand mediated by growth. However, GRC was not related to species growth rate, wood density, or drought and shade tolerance across the surveyed species nor across 27 tree species for which GRC was compiled. The GRC estimates based on wood chemical analysis were lower (0.19) than those based on gas exchange methods (0.35). These results give partial support to the hypothesis that wood production and maintenance costs are related to species ecology and highlight the divergence of respiratory parameters widely used in plant models according to the methodological approach applied to derive them.