Root Morphology and Rhizosphere Characteristics Are Related to Salt Tolerance of Suaeda salsa and Beta vulgaris L.

Abstract

Halophytes are capable of resisting salinity, and their root system is the part in direct contact with the saline soil environment. The aim of this study was to compare the responses of root morphology and rhizosphere characteristics to salinity between a halophyte, Suaeda salsa (suaeda), and a glycophyte, Beta vulgaris L. (sugar beet). The soil salt content was set to four levels (0.7, 1.2, 1.7, and 2.7%) by NaCl-treated plants. We investigated the soil pH, EC, nutrients and soil, plant ion (Na+, Cl−, K+, and Mg2+) concentration to evaluate the rhizospheric processes, and salt tolerance of suaeda by the root mat method. The highest biomass was in the 1.2% salt level for suaeda and in the 0.7% salt level for sugar beet. The root length and root surface area of suaeda showed similar trends to biomass, but the root diameter decreased by 11.5–17.9% with higher salinity. The Na+, Cl−, and K+ accumulations in the shoot of suaeda displayed higher than that in sugar beet, while the Mg2+ accumulation was lower in suaeda than that in sugar beet. High salinity resulted in increased pH and EC values in the rhizosphere for suaeda, but lower values of these parameters for sugar beet. Under high salinity, the Olsen phosphorus content was 0.50 g·kg−1 and 0.99 g·kg−1 higher in the rhizosphere than in the non-rhizosphere for suaeda and sugar beet. We concluded that the two species [halophyte, Suaeda salsa (suaeda), and a glycophyte, B. vulgaris L. (sugar beet)] showed diverse approaches for nutrient absorption under salinity stress. Suaeda altered its root morphology (smaller root diameter and longer roots) under salt stress to increase the root surface area, while sugar beet activated rhizospheric processes to take up more nutrients.

Nitrogen–Salt Interaction Adjusts Root Development and Ion Accumulation of the Halophyte Suaeda salsa

“…Additionally, an appropriate N level benefits halophytes, allowing them to increase their salt-tolerance capabilities. In addition, this study showed that a greater root length occurred at the 1.0% salt level, which was similar to the results of Wang et al [ 25 ]. This suggested that a certain amount of salt promotes the root formation of halophytic plants, whereas levels exceeding the threshold inhibit root formation.…”

“…To adapt to the non-homogeneity of nutrients and salt, root growth might show a strong plasticity response [ 24 ]. Moderate salt levels displayed a positive effect on root development for halophyte, but the stress from higher salt levels causes a negative effect, where it obtains more nutrients by increasing fine root presence in the subsoil [ 25 ]. N application would be bound to alter nutrient distributions in the topsoil and subsoil, which might produce an important influence on root architecture.…”

Salt and Drought Stress Responses in Cultivated Beets (Beta vulgaris L.) and Wild Beet (Beta maritima L.)

“…Despite the different results on root morphology of beet cultivars [61,81], alterations in root length are important adaptive strategies for plant stress tolerance [11,25,153]. Sugar beet and fodder beet are deep-rooted crops [40,48,63], and under water deprivation, fodder beet is able to extract water from bottom soil layers [63].…”

“…Sugar beet and fodder beet are deep-rooted crops [ 40 , 48 , 63 ], and under water deprivation, fodder beet is able to extract water from bottom soil layers [ 63 ]. However, sugar beet plants exposed to salt or drought stress displayed lower root length as compared to unstressed plants [ 54 , 153 ]. Among different sugar beet genotypes, salt-tolerant one (H30917) displayed longest root length as compared to other genotypes under salt stress [ 25 ].…”

“…Upon exposure to drought stress, the tolerant cultivar, 24367 produced more fibrous roots and displayed much reduction in shoot/root ratio and higher RWC levels compared to the sensitive cultivar, N6 [ 42 ]. In a very recent study, the shoot/root ratio decreased in sugar beet as the severity of salt stress increased [ 153 ]. Similarly, among salt/drought-tolerant wild beet varieties (CMP, OEI, and VMT), the CMP shows higher root/shoot ratio than the less tolerant ecotypes, which suggests that this wild beet ecotype can be useful for generating stress-tolerant beets [ 38 ].…”