PNNL

Abstract

Fine roots, the highly structured organs of trees responsible for the uptake and transport of resources, also directly or indirectly account for a majority of C sequestered in forest ecosystems. As they encounter frequent biotic and abiotic stresses in the soil environment, fine roots exhibit high plasticity to adapt to these stressful conditions. Although the morphological and physiological plasticity of roots has been well studied, less explored are the accompanying changes in the chemical construct of fine roots which we refer to as ‘chemical plasticity.' The chemical plasticity not only helps plants to adapt to environmental stress but also further alter their decomposability and potential to contribute to soil carbon. Here, we investigated the chemical plasticity of the different fine root orders of Quercus alba (white oak) and Quercus rubra (red oak) subjected to drought stress. Drought stress altered the quantity and composition of tannins; the quantity of condensed tannins increased while ellagitannins decreased in the 1+2 order roots exposed to drought compared to that in the ambient treatment which may have facilitated the higher ectomycorrhizal colonization in these fine roots. Unlike tannins, the total quantity of SVC lignins did not vary with drought. Our study also revealed for the first time that despite the lower quantity of SVC lignins in the 1+2 order roots, compared to the 3rd and 4th orders, the G lignins and bound phenolics that increase the integration of lignins with polysaccharides were higher in the 1+2 orders indicating that the 1+2 orders are better protected from biotic and abiotic stress due to their chemical construct which has implications for both plant adaptation and soil carbon sequestration. Our study for the first time revealed that the chemical construct of different heteropolymers such as lignins and tannins varied differently across root orders and when exposed to drought stress indicating the importance of chemical plasticity of fine roots to adapt to soil biotic and abiotic environment.