Phenotypic plasticity and water flux rates of Citrus root orders under salinity

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 describes 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, for example frequency of root orders, specific root area, cortical thickness, and xylem traits, did not change homogeneously throughout the root system, but changes after 6 months under 90 mM NaCl 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 2- to 6-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 C. 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.

It’s Complicated: Intraroot System Variability of Respiration and Morphological Traits in Four Deciduous Tree Species

“…The standard root order classes were not analyzed, because the datasets were nearly identical with the root diameter classes because of their diameter distributions. To determine species-specific RR Branch DWT , the average RR (RR DWT ) per root order class was weighted by the respective biomass (Rewald et al [2012] discuss a similar calculation with regard to branch water flux densities). This was done separately for the five dissected root systems per species, allowing us to use five true replicates per species for statistical analysis.…”

“…Although positive correlations between fine RR and nitrogen contents have been established, with young roots having greater nitrogen contents, much of the variation in RR rate within a diameter class must be caused by other factors (Pregitzer et al, 1998). In the last decade, evidence increased that root traits often vary according to the position of individual roots segments among the root branching hierarchy (Pagès and Kervella, 1990;Pregitzer et al, 2002;Wang et al, 2006;Guo et al, 2008aGuo et al, , 2008bValenzuela-Estrada et al, 2008;Beyer et al, 2013) and that analysis by root order is one powerful approach to understand complex woody root systems under stress (Rewald et al, 2012). Thus, it is surprising that few attempts (Jia et al, 2013) have been made to test if root order-based classification is covering root system heterogeneity in respiration in a meaningful way and morphological parameters on which it may be based.…”

Eficiência do hidrogel e respostas fisiológicas de mudas de cultivares apirênicas de citros sob défice hídrico

“…A capacidade de esta cultivar manter potenciais hídricos foliares adequados pode ser atribuída a características bioquímicas relacionadas à manutenção da capacidade de transporte de fotoassimilados da parte aérea para as raízes, possibilitando a absorção de água (Rewald et al 2012).…”

Root System Response to Drought and Salinity: Root Distribution and Water Transport

“…Such mechanisms can be functional and/or structural and include root architectural changes. In this sense, Rewald et al (2012) described the phenological and physiological plasticity of Citrus volkameriana rootstocks under severe salt stress, identifying a rapid and major modification of the root system involving a decrease in the surface root area and the number of lateral roots. This was indicative of a decrease in functionality in terms of uptake as several studies on woody species have remarked (Eshel and Waisel 1996;Croser et al 2001;Korn 2004).…”