Analysis of Water Supply of Plants under Saline Soils Conditions and Conclusions for Research on Crop Salt Tolerance (original) (raw)
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Root Morphology is a Key Factor to Improve Salt Tolerance of Soil-Grown Irrigated Crops
Abstract One promising strategy to combat agricultural losses caused by increasing soil salinity is the development of crops that are more tolerant to saline growth conditions. In the past decades research of plant salt tolerance focussed on the understanding of biochemical and physiological mechanism mainly happening inside organs of plants differing in their salt tolerance and growing under well-controlled soil-less conditions. This approach expanded our knowledge on hundreds of metabolic processes and detrimental effects significantly, but unfortunately most results did not contribute to improve salt tolerance of field-grown crops. Assuming that the cultivation of plants under hydroponic conditions was a major limitation, the focus of the presented approach to is soil-based. The classical concept of crop salt tolerance rating applied in irrigated agriculture is also soil-based, but considers only the vertical distribution of salts in the rooted soil layer, which results from controlled application of brackish waters. However, this concept does not consider that transpiration during periods of water depletion causes a separation of soil salinity between the rhizospheric soil volume occupied by roots and root hairs and the soil volume outside the rhizocylinder, the bulk soil. Basically, plant transpiration and exclusion of salts from root uptake divide the rooted soil layer into three fractions: (a) the rhizospheric soil, where soil meets root and where root water uptake and salt exclusion affect a build-up of soil water salinity, (2) the bulk soil, where soil water salinity is rarely affected, and (3) a transition zone between. Roots differ greatly in their ability to resist increasing soil water salinity and to form rhizospheric soil volumes. Pot experiments have shown that water uptake from soils of the same soil water salinity was about 350% higher by young rape plants (large rhizocylinder) as compared to young leek plants (small rhizocylinder). The results indicate a strong evidence that there is a strong relationship between root water uptake from saline soils and the soil volume directly affected by roots, the rhizocylinder. It is concluded that root morphology plays an important role for the salt tolerance of soil-grown crops. A model calculation shows the potential to improve salt tolerance of maize by modification of root morphology.
Root Morphology is a Key Factor to Improve Salt Tolerance of Soil-Grown Crops
One promising strategy to combat agricultural losses caused by increasing soil salinity is the development of crops that are more tolerant to saline growth conditions. In the past decades research of plant salt tolerance focussed on the understanding of biochemical and physiological mechanism mainly happening inside organs of plants differing in their salt tolerance and growing under well-controlled soil-less conditions. This approach expanded our knowledge on hundreds of metabolic processes and detrimental effects significantly, but unfortunately most results did not contribute to improve salt tolerance of field-grown crops. Assuming that the cultivation of plants under hydroponic conditions was a major limitation, the focus of the presented approach to is soil-based. The classical concept of crop salt tolerance rating applied in irrigated agriculture is also soil-based, but considers only the vertical distribution of salts in the rooted soil layer, which results from controlled application of brackish waters. However, this concept does not consider that transpiration during periods of water depletion causes a separation of soil salinity between the rhizospheric soil volume occupied by roots and root hairs and the soil volume outside the rhizocylinder, the bulk soil. Basically, plant transpiration and exclusion of salts from root uptake divide the rooted soil layer into three fractions: (a) the rhizospheric soil, where soil meets root and where root water uptake and salt exclusion affect a build-up of soil water salinity, (2) the bulk soil, where soil water salinity is rarely affected, and (3) a transition zone between. Roots differ greatly in their ability to resist increasing soil water salinity and to form rhizospheric soil volumes. Pot experiments have shown that water uptake from soils of the same soil water salinity was about 350% higher by young rape plants (large rhizocylinder) as compared to young leek plants (small rhizocylinder). The results indicate a strong evidence that there is a strong relationship between root water uptake from saline soils and the soil volume directly affected by roots, the rhizocylinder. It is concluded that root morphology plays an important role for the salt tolerance of soil-grown crops. A model calculation shows the potential to improve salt tolerance of maize by modification of root morphology.
In the past decades crop salt tolerance research focussed mainly on two important aspects: (a) study of the effects of vertical salt distribution in the rooted soil layer on crop salt tolerance, which is applied to manage crop growth on saline soils, (b) and to understand biochemical and physiological effects of salinity on plants at cell, tissue, organ and whole plant level as basic information to develop more salt tolerant plants. Unfortunately most biochemical and physiological findings were little relevant to improve plant growth under saline soils conditions. The objective of this paper is to point out an aspect that was rarely considered in the past decades, it is the effect of the transpiration driven lateral salt distribution around roots on crop salt tolerance. It is supposed that root morphology is a most important feature, which affects the process of salt accumulation around roots and thus water uptake from saline soils. Shoot transpiration causes a much steeper increase...
Root characteristics in salt tolerance
Root Research, 2003
The mechanisms of salt tolerance in plants were reviewed focusing on root characteristics of salt-tolerant cultivars under saline conditions. The salt-tolerant traits were characterized as greater root growth, higher efficiency in water uptake, lower Na+ permeability, better root osmotic adjustment, and higher root pressure. The roles of these characteristics in plant growth and crop production under saline conditions were discussed.
Agricultural Water Management, 2001
This publication is a complement to a previous publication on salt tolerance classi®cation, using the observations of a long-term experiment on the use of saline water. Three classi®cation methods were compared, based, respectively, on the electrical conductivity of the saturated paste extract, the relative evapotranspiration de®cit and the water stress day index. Among the eight crops grown during the experiment, broadbean, soybean and tomato were clearly distinguished by the methods based on the relative evapotranspiration de®cit and the water stress day index as more sensitive then durum wheat, maize, potato, sugar beet and sun¯ower. Their greater sensitivity may be explained by the salt sensitivity of rhizobium bacteria affecting the nitrogen supply, by the degree of osmotic adjustment or by the prolongation of the¯owering period.
Control of salt transport from roots to shoots of wheat in saline soil
Functional Plant Biology, 2004
Wheat genotypes with 5-fold difference in shoot Na+ concentrations were studied over a salinity range of 1–150 mm NaCl and CaCl2 of 0.5–10 mm to assess their performance in saline and sodic soils. All genotypes had a maximum shoot Na+ concentration at 50 mm external NaCl when the supplemental Ca2+ provided an activity of 1 mm or more. Shoot Na+ concentrations either stayed constant from 50 to 150 mm external NaCl, or decreased in some genotypes at the higher salinity. Calculated rates of root uptake, and root : shoot transport, were at a maximum at 50 mm NaCl in all genotypes, and decreased at higher NaCl in some genotypes, indicating feedback regulation. K+ showed a pattern inverse to that of Na+. Cl– uptake and transport rates increased linearly with increasing salinity, and differed little between genotypes. Increasing external Ca2+ concentration reduced the accumulation of Na+ in the shoot, the effects being greater in the low Na+ genotypes, and greater as the salinity increased...
ROOT MORPHOLOGY AND SEEDLING GROWTH OF THREE MALVACEOUS SALT TOLERANT PLANTS AT SALINE RHIZOSPHERE
The effects of salinity were studied on root morphology and seedling growth in thirty five day old Gossypium hirsutum, Kosteletzkya virginica and Thespesia populnea under different concentrations of sea salt solution i.e. non saline control (EC iw : 0.4 dS.m-1), 0.5% sea salt (EC iw : 6.2 dS.m-1), 1.0% sea salt (EC iw : 12.95 dS.m-1). Results showed that primary root length was reduced in K. virginica at 1.0% sea salt, while it remained almost unaffected in the other two plants at this salinity in comparison to control. Number of secondary roots increased in G. hirsutum and T. populnea but in K. virginica they show a slight decrease. All the three plants showed promotion in the length of secondary roots at 0.5% salinity. Number of tertiary roots was enhanced in T. populnea at 0.5% salinity level, whereas the other two plants exhibit inhibition of tertiary roots. Root biomass was increased in G. hirsutum at 0.5% salinity but decreased at higher salinity. K. virginica and T. populnea showed decrease with the increasing salinity. Fresh and dry shoot biomass and plant height showed a gradual decrease in response to increasing salinity in all the three species. The number of leaves decreased gradually in K. virginica and T. populnea as the salinity of the rooting medium increased, whereas, in G. hirsutum, the number of leaves decreased under saline condition but the number of leaves were more or less same under two salinity levels. Leaf area per plant of K. virginica and G. hirsutum gradually reduced with increasing salinity. In T. populnea leaf area increased at 0.5% salinity and decreased at 1.0% salinity level. T. populnea showed more uptake of Na + and K + under non saline condition as compared to the other two plants. Uptake of Na + increased with increasing salinity in all the three plants. K + concentration increased in roots of T. populnea and G. hirsutum and decreased in K. virginica at 0.5% salinity. At 1.0% salinity level K + concentration substantially decreased in all the three plants. The results showed that K. virginica was comparatively more tolerant under saline condition, where as G. hirsutum showed the comparatively least tolerance. Over all salt tolerance during growth of above mentioned three plants at higher level of salinity show that G. hirsutum was more tolerant, where as K. virginica showed the least tolerance at seedling stage.
Journal of Experimental Botany, 2016
The aim of this study was to investigate the effect of salinity stress on root growth at the phytomer level in wheat to provide novel site-specific understanding of salinity damage in roots. Seedlings of 13 wheat varieties were grown hydroponically. Plants were exposed to three concentrations of NaCl, 0 (control), 50 and 100 mM, from 47 days after sowing. In a destructive harvest 12 days later we determined the number of live leaves, adventitious roots, seminal roots and newly formed roots at the youngest phytomer; length and diameter of main axes; and length and diameter of root hairs and their number per millimetre of root axis. Elongation rate of main axes and root hair density were then derived. Root surface area at each root-bearing phytomer (Pr) was mechanistically modelled. New root formation was increased by salt exposure, while number of live leaves per plant decreased. The greatest salinity effect on root axis elongation was observed at the youngest roots at Pr1 and Pr2. Both the 50 mM and the 100 mM levels of salinity reduced root hair length by approximately 25% and root hair density by 40% compared with the control whereas root hairs alone contributed around 93% of the estimated total root surface area of an individual tiller. Decrease in main axis length of new roots, root hair density and root hair length combined to reduce estimated root surface area by 36-66% at the higher NaCl concentration. The varietal response towards the three salinity levels was found to be trait-specific. The data highlight reduction in root surface area as a major but previously largely unrecognized component of salinity damage. Salinity resistance is trait-specific. Selection for retention of root surface area at a specific phytomer position following salt exposure might be useful in development of salinity-tolerant crop varieties.