Tree age and root order affect the adaptation of fine roots to the surrounding environment: a case study of Pinus koraiensis

Abstract

Abstract Aims Fine roots adjust their traits during tree growth to adapt to changes in environments, but may vary by root order. We aim to separate the influence of ontogeny and root order on root trait plasticity.Methods We examined six morphological and anatomical traits of the first five order fine roots for 67 Pinus koraiensis individuals aged 16 to 285 years in northeast China, while quantifying soil water and N content.Results As trees aged, the specific root length (SRL) of first- to fifth-order roots increased linearly but root tissue density (RTD) decreased non-linearly; the root diameter (RD) and cortex thickness (CT) of second-order roots and the stele-to-root diameter ratio (SDR) of third- and fourth-orders increased; the difference values in SRL and SDR among root orders increased. CT of first-order roots increased with soil water content but SDR decreased. CT of third-order roots was affected by both soil water and N content. Furthermore, with increasing tree age, there was a trade-off between SRL and RTD of the first five orders and a collaborated increase in RD and stele diameter (SD); RD and CT of first- and second-orders also increased collaboratively.Conclusions Our study not only reflects changes in fine root strategies at different ontogeny stages, but also reveals differences in the plasticity of fine roots to the surrounding environment at different root orders. Moreover, covariation in multiple intraspecific trait syndromes with tree age suggests multiple ongoing strategies to adjust to changing environments, while highlighting the inherent heterogeneity within fine roots.