Xylem and soil CO2 fluxes in a Quercus pyrenaica Willd. coppice: root respiration increases with clonal size

Abstract

• Key message: Xylem and soil CO2fluxes in coppiced oak forests increase with clonal size, suggesting larger expenditures of energy for root respiration. An imbalance between root demand and shoot production of carbohydrates may contribute to the degradation of abandoned coppices. • Context: Our understanding of root respiration is limited, particularly in root-resprouting species with many stems and a large system of interconnected roots resulting from long-term coppicing. • Aims: We tested the hypothesis that clone size influences the internal flux of CO2 dissolved in xylem sap (FT) from roots into the stem and soil CO2 efflux (FS) as indicators of root respiration. We predicted that large clones would exhibit higher FT per stem and FS than small clones due to larger root system per stem in large clones. • Methods: Genetic analyses were performed to elucidate clonal grouping. FT was measured continuously for 100 days in 16 similar-sized stems of Quercus pyrenaica belonging to two large and two small clones. FS was measured in 20 clones of varying size. • Results: FT per stem and FS were higher in large clones. FT was 2 % of the root-respired CO2 that diffused through soil to the atmosphere. • Conclusions: Relative to other studies, the contribution of FT to root respiration was very low, pointing to large differences depending on species or site. Higher stem FT and FS in large clones compared with small clones suggest greater carbon consumption by roots in large clones, pointing to a root/shoot biomass and physiological imbalance resulting from long-term coppicing that would partially explain the degradation of currently abandoned stands of Q. pyrenaica.