Vertical fine-root distributions in five subalpine forest types shifts with soil properties across environmental gradients

Abstract

Vertical fine-root distribution determines the potential for acquisition of resources throughout soil profiles; yet, variation among forest types and changes in vertical distribution with environments are poorly understood. We examined vertical root distributions of different forest communities to determine how belowground strategies shift across different forest types and along edaphic gradients. Specific root length and diameter of fine roots as well as fine-root biomass, length and area densities were measured in sequential soil layers at 10 cm depth increments across 118 forest plots representing five subalpine forest types. Evergreen forest types, including evergreen oaks, were more deeply rooted than birch forests. Differences in rooting depth were due to the dominant tree species identity, not to variations in shrub or herbaceous components. Within forest types, soil nutrients and physical properties contributed to shifts rooting depth but not root morphology. Vertical distributions of fine roots represent critical inputs of plant carbon into soils as well as different capacities for the acquisition of soil resources. Our findings identify consistent patterns of rooting distributions among forest types that may be predictable based on more easily measured root and soil properties and can improve efforts to model rooting depth profiles in forest communities.