ABSTRACT: Knowledge about the root system structure and the uptake efficiency of root orders is critical to understand the adaptive plasticity of plants towards salt stress. Thus, this study is describing the phenological and physiological plasticity of Citrus volkameriana rootstocks under severe NaCl stress on the level of root orders.
Phenotypic root traits known to influence uptake processes, e.g. frequency of root orders, specific root area, cortical thickness and xylem traits, did not change homogeneously throughout the root system but changes under stress were root order-specific. Chloride accumulation significantly increased with decreasing root order and the Cl concentration in lower root orders exceeded those in leaves. Water flux densities of first order roots decreased to <20% under salinity and did not recover after stress release. The water flux densities of higher root orders changed marginally under salinity and increased two to six-fold in second and third root orders after short-term stress release.
Changes in root order frequency, morphology and anatomy indicate rapid and major modification of Citrus volkameriana root systems under salt stress. Reduced water uptake under salinity was related to changes of water flux densities among root orders and to reduced root surface areas. The importance of root orders for water uptake changed under salinity from root tips towards higher root orders. The root order-specific changes reflect differences in vulnerability (indicated by the salt accumulation) and ontogenetic status and point to functional differences among root orders under high salinity.
Journal of Experimental Botany 01/2012; 63(7):2717-2727. · 5.36 Impact Factor