Changes in root characteristics, gas exchange and water use efficiency following water stress and rehydration of Alfalfa and Sorghum

Abstract Soil water stress has paramount effects on water uptake by roots and its use by shoots. In this study, we determined changes in root hydraulic conductivity (Lp r ) and morphology under drought stress and how they regulate shoot gas exchange and water use efficiency in alfalfa and sorghum, two crops with contrasting adaptations to drought, the former exhibiting strong drought avoidance and the later strong drought tolerance. Seedlings of two alfalfa cultivars differing in drought avoidance and one highly drought tolerant sorghum cultivar were subjected to PEG-6000-induced water stress and then rehydrated. The Lp r declined rapidly after the PEG treatment but largely recovered within 48 hours of rehydration; however, inter-specific and cultivar differences were significant. The rapid change in Lp r also led to equally rapid changes in leaf water potential, gas exchange and consequently, the instantaneous water use efficiency (WUE i ) in both species. A reasonable correlation was found between Lp r and WUE i . Treatment with Hg 2+ indicated that the water stress-induced changes in Lp r were due to the involvement of aquaporins. One year old alfalfa and sorghum cultivars subjected to moderate and severe drought stress at the field level had altered root morphology and reduced biomass production and water dissipation but increased water use efficiency of biomass production (WUE b ). These changes were dependent on stress level, species and cultivars. However, not all the root morphological changes contributed to improved water use. For example, the decrease in taproot length negatively affected the WUE b of alfalfa whereas the increase in root surface area was positively related only to the WUE b of sorghum. The difference in drought tolerance between species or cultivars was related to their ability to recover the lost Lp r and CO 2 assimilation after rehydration, as well as the ability to effectively regulate root morphological changes to increase WUE. Keywords: Root hydraulic conductivity, drought tolerance (DT), gas exchange, water use efficiency(WUE), alfalfa(A) and sorghum (S). Abbreviations: Lp r -root hydraulic conductivity; WUE i -instantaneous water use efficiency; WUE b -water use efficiency of biomass production; R/S-ratio of root and shoot; MC-mercury chloride; β-ME-β-mercaptoethanol; RVR-the relative variation rate; Ψ leaf -leaf water potential; Pn-including net CO 2 assimilation rate; Gs-stomatal conductance; Tr-transpiration rate; C i -intercellular CO 2 -concentration; WDT-water dissipation by transpiration; DSI above or DSI below -the above-or belowground dry substance stress index; RGR-the relative growth rate root length, SR-root surface area; NR-number of roots (Diameter≥ 1mm); WR-width of tap/seminal roots; LTR-the length of taproot; TLR-total length of roots; MS-Moderate stress; SS-Severe stres

Salinity Effects on Morpho-Physiological and Yield Traits of Soybean (Glycine max L.) as Mediated by Foliar Spray with Brassinolide

Salinity episodes that are common in arid regions, characterized by dryland, are adversely affecting crop production worldwide. This study evaluated the effectiveness of brassinolide (BL) in ameliorating salinity stress imposed on soybean at four levels (control (1.10), 32.40, 60.60 and 86.30 mM/L NaCl) in factorial combination with six BL application frequency (control (BL0), application at seedling (BL1), flowering (BL2), podding (BL3), seedling + flowering (BL4) and seedling + flowering + podding (BL5)) stages. Plant growth attributes, seed yield, and N, P, K, Ca and Mg partitioning to leaves, stems and roots, as well as protein and seed-N concentrations, were significantly (p ≤ 0.05) reduced by salinity stress. These trends were ascribed to considerable impairments in the photosynthetic pigments, photosynthetically active radiation, leaf stomatal conductance and relative water content in the leaves of seedlings under stress. The activity of peroxidase and superoxidase significantly (p ≤ 0.05) increased with salinity. Foliar spray with BL significantly (p ≤ 0.05) improved the photosynthetic attributes, as well as nutrient partitioning, under stress, and alleviated ion toxicity by maintaining a favourable K+/Na+ ratio and decreasing oxidative damage. Foliar spray with brassinolide could sustain soybean growth and seed yield at salt concentrations up to 60.60 mM/L NaCl

Effects of non-uniform root zone salinity on water use, Na+ recirculation, and Na+ and H+ flux in cotton

A new split-root system was established through grafting to study cotton response to non-uniform salinity. Each root half was treated with either uniform (100/100 mM) or non-uniform NaCl concentrations (0/200 and 50/150 mM). In contrast to uniform control, non-uniform salinity treatment improved plant growth and water use, with more water absorbed from the non- and low salinity side. Non-uniform treatments decreased Na+ concentrations in leaves. The [Na+] in the ‘0’ side roots of the 0/200 treatment was significantly higher than that in either side of the 0/0 control, but greatly decreased when the ‘0’ side phloem was girdled, suggesting that the increased [Na+] in the ‘0’ side roots was possibly due to transportation of foliar Na+ to roots through phloem. Plants under non-uniform salinity extruded more Na+ from the root than those under uniform salinity. Root Na+ efflux in the low salinity side was greatly enhanced by the higher salinity side. NaCl-induced Na+ efflux and H+ influx were inhibited by amiloride and sodium orthovanadate, suggesting that root Na+ extrusion was probably due to active Na+/H+ antiport across the plasma membrane. Improved plant growth under non-uniform salinity was thus attributed to increased water use, reduced leaf Na+ concentration, transport of excessive foliar Na+ to the low salinity side, and enhanced Na+ efflux from the low salinity root

An Evaluation of Input–Output Value for Sustainability in a Chinese Steel Production System Based on Emergy Analysis

The social investment, natural resource consumption, and pollutant emissions involved in steel production can be evaluated comprehensively using the emergy analysis. We explored the sustainability of the steel production system from four aspects: input index, output index, input⁻output index, and sustainability index. The results showed that the maximum inputs were the intermediate product/recyclable materials produced within the production line; energy sources were mainly non-renewable and the emergy value of pollutants discharged was rather low. The environmental load rate of the pelletizing and sintering processes were the highest and the proportion of recycled materials for puddling and steel-making were the highest. The emergy investment rate of rolling was the highest; the emergy value of the pollutants discharged in each process was very small, and the emergy yield ratio was highest in the rolling process. Pelletizing, sintering, and steel-making were input consuming processes, but the sustainability index of puddling and rolling processes was sound. The whole process line can be sustainable, considering the useful intermediate and recyclable products

Using Modified Remote Sensing Imagery to Interpret Changes in Cultivated Land under Saline-Alkali Conditions

Managing the rapidly changing saline-alkali land under cultivation in the coastal areas of China is important not only for mitigating the negative impacts of such land on the environment, but also for ensuring long-term sustainability of agriculture. In this light, setting up rapid monitoring systems to assist decision-making in developing sustainable management plans is therefore an absolute necessity. In this study, we developed a new interpretation system where symbols are used to grade and classify saline-alkali lands in space and time, based on the characteristics of plant cover and features of remote sensing images. The system was used in combination with the maximum likelihood supervised classification to analyze the changes in cultivated lands under saline-alkali conditions in Huanghua City. The analysis revealed changes in the area and spatial distribution of cultivated under saline-alkali conditions in the region. The total area of saline-alkali land was 139,588.8 ha in 1992 and 134,477.5 ha in 2011. Compared with 1992, severely and moderately saline-alkali land areas decreased in 2011. However, non/slightly saline land areas increased over that in 1992. The results showed that the salinization rate of arable lands in Huanghua City decreased from 1992 to 2011. The moderately saline-alkali land southeast of the city transformed into non/slightly saline-alkaline. Then, severely saline-alkali land far from the coastal zone west of the city became moderately saline-alkaline. Spatial changes in cultivated saline-alkali lands in Huanghua City were such that the centers of gravity (CG) of severely and non/slightly saline-alkali land moved closer the coastline, while that of the moderately saline-alkali land moved from southwest coastal line to northwest. Factors influencing changes in cultivated lands in the saline-alkali ecosystem included climate, hydrology and human activity. Thus, studies are required to further explore these factors in order to build a better understanding into the relative contributions of the changes saline-alkali state on the functions of coastline ecosystems

Calcium effects on root cell wall composition and ion contents in two soybean cultivars under salinity stress

It has been widely suggested that calcium (Ca) application ameliorates salt stress, but characteristic changes in root cell wall due to Ca application under saline conditions are poorly documented. Our objectives were: (1) to determine the effect of Ca on root cell wall composition, using two soybean cultivars differing in sensitivity to salt stress and (2) to understand the relationship between the internal effects of sodium-calcium interaction on the root cell wall. Uniform seedlings were transplanted into mixed solutions of NaCl (0, 40 mM,) and CaCl2 (0, 0.5, 2 mM). Root lengths were measured after an exposure of 14, 24 and 40 h to the treatments and cell wall analysis performed for total sugars, uronic acid and ion contents. Without salinity stress, Ca application caused no significant changes in root growth and cell wall constituents in both cultivars. However, it did ameliorate the decrease in the amount of cell wall under stress, especially the pectin fraction. Both cell wall and cellular Ca2+ and K+ contents were significantly increased by additional Ca2+ under saline condition. Therefore, by applying Ca2+, the maintenance of pectin level and increase in cell wall Ca2+ may contribute to the restoration of root growth under salinity. Calcium application significantly increased the pectin level under salinity and soybean root growth also showed notable restoration. One way Ca ameliorates salt toxicity may be by maintaining the composition of the cell wall. This ameliorative effect was more conspicuous in the salt-tolerant cultivar, Dare, than the salt-sensitive cultivar, Touzan 69

Transcriptome Analysis Unravels Key Factors Involved in Response to Potassium Deficiency and Feedback Regulation of K+ Uptake in Cotton Roots

To properly understand cotton responses to potassium (K+) deficiency and how its shoot feedback regulates K+ uptake and root growth, we analyzed the changes in root transcriptome induced by low K+ (0.03 mM K+, lasting three days) in self-grafts of a K+ inefficient cotton variety (CCRI41/CCRI41, scion/rootstock) and its reciprocal grafts with a K+ efficient variety (SCRC22/CCRI41). Compared with CCRI41/CCRI41, the SCRC22 scion enhanced the K+ uptake and root growth of CCRI41 rootstock. A total of 1968 and 2539 differently expressed genes (DEGs) were identified in the roots of CCRI41/CCRI41 and SCRC22/CCRI41 in response to K+ deficiency, respectively. The overlapped and similarly (both up- or both down-) regulated DEGs in the two grafts were considered the basic response to K+ deficiency in cotton roots, whereas the DEGs only found in SCRC22/CCRI41 (1954) and those oppositely (one up- and the other down-) regulated in the two grafts might be the key factors involved in the feedback regulation of K+ uptake and root growth. The expression level of four putative K+ transporter genes (three GhHAK5s and one GhKUP3) increased in both grafts under low K+, which could enable plants to cope with K+ deficiency. In addition, two ethylene response factors (ERFs), GhERF15 and GhESE3, both down-regulated in the roots of CCRI41/CCRI41 and SCRC22/CCRI41, may negatively regulate K+ uptake in cotton roots due to higher net K+ uptake rate in their virus-induced gene silencing (VIGS) plants. In terms of feedback regulation of K+ uptake and root growth, several up-regulated DEGs related to Ca2+ binding and CIPK (CBL-interacting protein kinases), one up-regulated GhKUP3 and several up-regulated GhNRT2.1s probably play important roles. In conclusion, these results provide a deeper insight into the molecular mechanisms involved in basic response to low K+ stress in cotton roots and feedback regulation of K+ uptake, and present several low K+ tolerance-associated genes that need to be further identified and characterized

Effects of Zeolite on soil nutrients and growth of barley following irrigation with saline water

The 3rd International Conference on Water Resources and Arid Environments (2008) and the 1st Arab Water Forum .Soil salinity is a major abiotic factor limiting crop production but an amendment with synthetic zeolite may mitigate effects of salinity stress on plants. The objective of the study was to determine the effects of zeolite on soil properties and growth of barley irrigated with diluted seawater. Barley was raised on a sand dune soil treated with calcium type zeolite at the rate of 1 and 5% and irrigated every alternate day with seawater diluted to electrical conductivity (EC) levels of 3 and 16 dS m-1. Irrigation with 16 dS m-1 saline water significantly suppressed plant height by 25%, leaf area by 44% and dry weight by 60%. However, a substantial increase in plant biomass of salt stressed barley was observed in zeolite-amended treatments. The application of zeolite also enhanced water and salt holding capacity of soil. Post-harvest soil analysis showed high concentrations of Ca2+, Mg2+, Na+ and K+ due to saline water especially in the upper soil layer but concentrations were lower in soils treated with zeolite. The overall results indicated that soil amendment with zeolite could effectively ameliorate salinity stress and improve nutrient balance in a sandy soil