Linking fine root morphology, hydraulic functioning, and shade tolerance of trees

Authors: ZADWORNY, MARCIN - Polish Academy Of Sciences; Comas, Louise; EISSENSTAT, DAVID - Pennsylvania State University

Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2018
Publication Date: 4/20/2018
Citation: Zadworny, M., Comas, L.H., Eissenstat, D.M. 2018. Linking fine root morphology, hydraulic functioning, and shade tolerance of trees. Annals of Botany. 122(2):239-250. doi:10.1093/aob/mcy054.
DOI: https://doi.org/10.1093/aob/mcy054

Interpretive Summary: Understanding root traits and trade-offs in their functioning is important for understanding plant functioning in natural ecosystems as well as agricultural systems. The aim of the present study was to determine the relationship between root morphology and the hydraulic characteristics of fine roots for species differing in shade tolerance. Root morphological, anatomical, and hydraulic traits were measured in tree species with different levels of shade tolerance and life history strategies. Compared to shade-tolerant species, shade-intolerant species produced thinner absorptive roots with smaller diameter xylem conducting elements and underwent secondary development less frequently, suggesting they had shorter lifespan. Shade-tolerant species had greater root specific hydraulic conductance among these roots due to having larger diameter xylem, although these roots had a lower calculated critical tension for conduit collapse. In addition, shade-intolerant species exhibited greater variation in hydraulic conductance across different root growth rings produced in different years as compared to shade-tolerant species. Collectively, these data suggest that shade-intolerant species are more plastic than shade-tolerant species in their ability to develop a root system of sufficient hydraulic capacity to fulfill the rapid water uptake needed for rapid shoot growth while still producing thin absorptive roots that can proliferate quickly for nutrient foraging.

Technical Abstract: Understanding root traits and trade-offs in their functioning is important for understanding plant functioning in natural ecosystems as well as agricultural systems. The aim of the present study was to determine the relationship between root morphology and the hydraulic characteristics of fine roots (< 2 mm) for species differing in shade tolerance (low, moderate and high). The morphological, anatomical, and hydraulic traits across five distal root orders were measured in species with different levels of shade tolerance and life history strategies. Species included Acer negundo, Acer rubrum, Acer saccharum, Betula alleghaniensis, Betula lenta, Quercus alba, Quercus rubra, Pinus strobus, and Pinus virginiana. Compared to shade-tolerant species, shade-intolerant species produced thinner absorptive roots with smaller xylem lumen diameters and underwent secondary development less frequently, suggesting they had shorter lifespan. Shade-tolerant species had greater root specific hydraulic conductance among these roots due to having larger diameter xylem, although these roots had a lower calculated critical tension for conduit collapse. In addition, shade-intolerant species exhibited greater variation in hydraulic conductance across different root growth rings in woody transport roots of the same root order as compared to shade-tolerant species. Collectively, these data suggest that shade-intolerant species are more plastic than shade-tolerant species in their ability to develop a root system of sufficient hydraulic capacity to fulfill the rapid water uptake needed for rapid shoot growth while still producing thin absorptive roots that can proliferate quickly for nutrient foraging.