Functional relationships between morphology and respiration of fine roots in two Chinese temperate tree species

Fine root morphology is closely linked with physiological functions. However, we have limited understanding of relationships between morphological traits and respiration of fine roots. In this study, we measured the fine root respiration rates of Tilia amurensis Rupr. and Pinus koraiensis Sieb. et Zucc with a simplified specially designed root-chamber system in the field. We found that mean diameter and specific root length (SRL) exhibited significant power relationships with fine root respiration in both species. Respiration rates of smaller fine roots (< 0.5 mm for Tilia amurensis and < 0.7 mm for Pinus koraiensis) in mean diameter were much higher and varied widely compared with those larger diameter class (0.6-1.8 mm for Tilia amurensis and 0.8-1.9 mm for Pinus koraiensis). Moreover, significant positive relationships existed between fine root nitrogen (N) concentration and respiration in both species. For Tilia amurensis, SRL explained more of the variability in respiration (84%) than diameter or N concentration, while for Pinus koraiensis, fine root N concentration explained more of the variability in respiration (79%) than diameter or SRL. Our results suggest that fine roots are composed of individual roots differing markedly in respiration and morphology, rather than identical units as traditionally assumed.