Fine roots (traditionally defined as ≤2mm diameter), are highly structured organs of plants responsible for water and nutrient uptake. Fine roots reside in a soil environment that is highly heterogeneous in the availability of water. Projected increase in warming and frequent droughts would further exacerbate moisture limitation in soils. Well studied are the morphological adaptations of roots in response to these environmental stresses. However, roots also undergo changes in the content and composition of heteropolymers that further alter their decomposability and potential to contribute to soil carbon. We studied the morphological and chemical plasticity of different orders of fine root of Quercus rubra and Q. albasubjected to drought conditions using microscopic and mass spectrometric techniques.
Results/Conclusions
Roots exposed to drought had higher specific root length had higher mycorrhizal association compared to roots produced under ambient conditions. The morphological changes and mycorrhizal associations altered the anatomy, chemical composition and organization of biopolymers within the fine root matrix. The first and second order roots of Quercus alba exposed to drought conditions had lower SVC lignin content [sum of vanillyls (V; synonym guaiacyl, G), syringyl (S), cinnamyl (C) phenols], but twofold higher abundance of crosslinking H-units than the roots developed under ambient moisture. Similarly, tannin content of the root formed under drought treatment were higher and most of the tannins were associated with cell walls. Our results indicate that the roots formed under drought could potentially be more resistant to decomposition than roots formed under optimal moisture. As a majority of soil carbon are fine root derived these changes in the chemistry of fine roots would have far reaching implications for soil carbon storage under future climates.