Fine-root respiration and exudation together accounted for half of the total carbon (C) allocation to fine roots. The labile substrates released to the surrounding soils as root exudation stimulates microbial activity and decomposition of soil organic matter, which further affects soil C cycling. Although evidence showed that fine-root exudation positively related with respiration within species, how these fluxes relate with each other among species is not known. We measured the fine-root exudation and respiration on the first-three-order root branches from 19 co-existing woody species in the Hubei Province, central China in July, 2018. The fine-root exudation was measured in situ with a syringe-based cultivation and the fine-root respiration was measured with a static chamber method. Root chemical (C and nitrogen (N) concentration) and morphological (diameter, specific root length, branching intensity) traits were also measured.
Results/Conclusions
We found a positive correlation between fine-root respiration and exudation among target species. This correlation existed when phylogenetic signals were considered. Similarly, root exudation also positively correlated with root N concentration, suggesting that N-rich active roots tended to release more root exudation. A principal component analysis (PCA) showed that root functional traits measured distributed along two major axes. Fine-root respiration and exudation, as well as root N concentration and tissue density were on PCA1 axis, while morphological traits were on PCA2 axis. Our results suggested that fine-root exudation rate is a major physiological trait in the root-trait syndrome.