Anatomically defined absorptive fine roots are modulated by root-order architecture and morphology during tree ontogeny

Abstract

Aims

Absorptive fine roots play an important role in resource uptake and belowground carbon allocation in woody plants. However, information on how their composition, biomass and length change with tree age remains limited.

Methods

We selected young and mature trees of four temperate species with distinct root diameter size, comprising thin-root species Fraxinus mandshurica and Larix gmelinii, and thick-root species Phellodendron amurense and Pinus koraiensis. Root biomass, length, anatomy, morphology, and architecture were determined in undamaged fine root branches.

Results

Based on anatomical observations, absorptive fine roots (exhibit primary development with intact cortex) predominantly comprised first- to third-order roots from young to mature trees across all species. The proportion of absorptive fine root biomass to the total fine root biomass (PARB) increased significantly with tree age, whereas the proportion of absorptive fine root length to the total fine root length (PARL) remained unchanged. Regardless of age group, PARB and PARL in thin-root species of F. mandshurica and L. gmelinii were significantly higher than those in thick-root species of P. amurense and P. koraiensis. The variation in PARB was mainly influenced by the proportions of first- to fifth-order root biomass to total fine root biomass and root diameter. The variation in PARL was mainly influenced by the proportions of first- to fifth-order root length to total fine root length, specific root length, and branching ratio.

Conclusions

Our findings suggest that absorptive fine root biomass changes during ontogenetic stage, which may influence belowground carbon allocation and resource competition.