Water‐stress mitigation by selenium in Trifolium repens L.

This study was designed to examine whether external selenium (Se) may improve the tolerance of Trifolium repens L. to polyethylene glycol (PEG)–induced water deficit, and to determine the physiological mechanisms of the possibly enhanced tolerance. Trifolium repens seedlings were subjected to PEG‐induced water deficit alone or combined with 5 μM Na₂SeO₄ for 24, 48, and 72 h. During the experimental period, the fresh weight (FW) of T. repens seedlings and the relative water content (RWC) of the leaves decreased gradually, and the chlorophyll concentration increased after 24 and 48 h, but decreased after 72 h. The PEG+Se‐treated plants had higher FW, RWC, and chlorophyll concentration than the PEG‐treated plants. Smaller amounts of thiobarbituric acid‐reactive substances (TBARS) and H₂O₂ accumulated in PEG+Se‐treated plants than in plants treated only with PEG. The activity of superoxide dismutase (SOD) increased gradually during the water‐deficit period, and Se application promoted SOD activity further. Catalase (CAT) activity remained unchanged after 24 and 48 h and insignificantly increased after 72 h of water deficit, whereas ascorbate peroxidase (APOX) activity increased linearly and glutathione reductase (GR) activity increased slightly over the course of treatment. Whereas the Se application exhibited no effect on the CAT activity, seedlings treated with PEG+Se had higher APOX activity during the whole experimental period and a higher GR activity after 48 and 72 h than PEG‐treated plants. These results suggest that exogenous Se treatment enhanced T. repens tolerance to PEG‐induced water deficit, and this enhancement was related to alleviation of lipid peroxidation and activation of antioxidant enzymes such as SOD, APOX, and GR.     

Sodium‐calcium interactions with growth,water, and photosynthetic parameters in salt‐treated beans

Calcium (Ca²⁺) amelioration of the plant's growth response to salinity depends on genetic factors. In this work, supplemental Ca²⁺ did not improve growth in Phaseolus vulgaris L. cv. Contender under high‐saline conditions and negatively affected several physiological parameters in nonsalinized plants. The response to supplemental Ca²⁺ was examined using plants grown in 25% modified Hoagland solution at different Na⁺ : Ca²⁺ ratios. In control plants (1 mM Ca²⁺; 1 mM Na⁺) surplus Ca²⁺ (4 or 10 mM) was associated with stomatal closure, decrease of hydraulic conductivity, sap flow, leaf specific dry weight, leaf K⁺ and leaf Mg²⁺ concentrations, and inhibition of CO₂ assimilation. Leaf water content was enhanced, while water‐use efficiency and dry matter were unaffected during the 15 d experimental period. The Ca²⁺ effect was not cation‐specific since similar results were found in plants supplied with high external Mg²⁺ or with a combination of Ca²⁺ and Mg²⁺. Relative to control plants, salinization (50 and 100 mM NaCl) caused a decrease in dry matter, hydraulic conductivity, sap flow, leaf Mg²⁺ activity, and inhibition of stomatal opening and CO₂ assimilation. However, NaCl (50 and 100 mM NaCl) enhanced leaf K⁺ concentration and water‐use efficiency. At 100 mM NaCl, leaf water content also significantly increased. Supplemental Ca²⁺ had no amelioration effect on the salt‐stress response of this bean cultivar. In contrast, the 50 mM–NaCl treatment improved stomatal conductance and CO₂‐assimilation rate in plants exposed to the highest Ca²⁺ concentration (10 mM). Phaseolus vulgaris is classified as a very NaCl‐sensitive species. The similarities in the effects caused by supplemental Ca²⁺, supplemental Mg²⁺, and NaCl salinity suggest that P. vulgaris cv. Contender has a high non‐ion‐specific salt sensitivity. On the other hand, the improvement in gas‐exchange parameters in Ca²⁺‐supplemented plants by high NaCl could be the result of specific Na⁺‐triggered responses, such as an increase in the concentration of K⁺ in the leaves.     

硅对植物体中某些营养物质穿细胞及质外体吸收的影响

The positive effects of silicon（Si） on growth of plants have been well documented;however,the impact of Si on plant nutrient uptake remains unclear.The growth,nutrient content and uptake of wheat（Triticum aestivum L.）,canola（Brassica napus L.） and cotton（Gossypium hirsutum L.） plants were evaluated with or without application of 1.5 mmol L^-1 Si.Application of Si increased dry weights by 8%,30%and 30%and relative growth rate（RGR） by 10%,13%and 17%in the cotton,canola and wheat plants,respectively.The plant relative water content（RWC） was also increased,but the plant transpiration was decreased by Si application.The uptake and content of Ca²⁺ were 19%and 21%lower in the cotton and wheat plants with Si than those without Si,respectively;however,Si application increased both K⁺ and Fe uptake and contents in all plant species.Silicon application reduced B uptake and content only in cotton and increased P and Zn²⁺ contents in all three plant species.The decrease in Ca²⁺ uptake by Si application was sustained even in the presence of metabolic inhibitors 2,4-dinitrophenol and sodium cyanide.Uptake of Ca²⁺ by Si application was enhanced or did not change when plant shoots were saturated with water vapor or their roots were exposed to low temperature.Thus,Si application increased the uptake of transcellularly transported elements like K⁺,P,Zn²⁺ and Fe.In contrast,Ca2+ uptake which occurred via both apoplastic and transcellular pathways was decreased by Si application,possibly through reduction of apoplastic uptake.More efficient nutrient uptake might be another promoting effect of Si on plant growth.     

High monosilicic acid supply rapidly increases Na accumulation in maize roots by decreasing external Ca2+ activity

Both calcium (Ca²⁺) and silicon (Si) improve plant performance under salt (NaCl) stress. Although these two mineral elements share numerous similarities, the information on how their extracellular interactions in the root apoplast affect uptake of sodium (Na⁺) is still lacking. Here, we investigated the effect of high Si supply in the bioavailable form of monosilicic acid (H₄SiO₄) on the activity of Ca²⁺ in the external root solution, and subsequent root uptake and compartmentation of Na in maize (Zea mays L.). In the short‐term experiments (6 h), 14‐d‐old maize plants were exposed to various concentrations of Ca²⁺ at three different pH‐values (6.5, 7.5, and 8.5) and two Si concentrations, i.e., low (1 mM) and high (4 mM) supply of H₄SiO₄. The activity of Ca²⁺ and Na⁺ in the external solution as well as the root concentrations of total and cell sap and BaCl₂‐exchangeble apoplastic fractions of both elements were analyzed. The pH of the nutrient solution affected neither the ion activities nor the root accumulation of both Ca²⁺ and Na⁺. At higher pH values (7.5 and 8.5) the interactions of Ca²⁺ and Si at high Si supply led to a decrease of Ca²⁺ activity and, hence, an increase of Na⁺ : Ca²⁺ activity ratio in the external root solution. Concomitantly, despite the elevated exchangeable apoplastic fraction of both Ca²⁺ and Na⁺, the total and cell sap concentrations were remarkably decreased for Ca²⁺ and increased for Na⁺ by the addition of 4 mM H₄SiO₄. This work demonstrates that at high Si supply extracellular Ca‐Si interactions leading to lowered activity of Ca²⁺ might rapidly compromise the ameliorative effect of Ca²⁺ on Na⁺ accumulation in roots. Practically, Si over‐fertilization of saline and, in particular, sodic soils may further promote the accumulation of Na⁺ in root tissues hours after Si application and, hence, increase a potential risk of Na⁺ toxicity.     

Morpho-physiological and yield responses to exogenous moringa leaf extract and salicylic acid in maize (Zea mays L.) under water stress

Two field experiments were executed to investigate the effects of foliar-applied moringa (Moringa oleifera) leaf extract (MLE; 1:30 w/v) and salicylic acid (SA; 0.5 mmol), singly or in combination, on growth, physio-biochemical, yield attributes and water use efficiency (WUE) of maize (Zea mays L., Three Ways Cross 329) under full and deficit irrigation conditions. Deficit irrigation was carried out by withholding water for 36 d from 12 to 48 days after sowing (DAS). At vegetative stage, deficit irrigation signi?cantly decreased all growth criteria, chlorophyll a concentration, and relative water content (RWC). In contrast, deficit irrigation considerably increased the concentrations of carotenoids, proline, membrane permeability (MP) and malondialdehyde (MDA). Similarly, grain yield, most yield components and WUE were significantly depressed in drought-stressed plants. However, foliar-applied treatments particularly MLE+SA signi?cantly increased growth traits, photosynthetic pigments, RWC and proline accumulation associated with a simultaneous decrease in MP and MDA concentration under full and deficit irrigation conditions. The application of MLE+SA markedly increased grain yield, yield components and WUE over control (spray tap water). Overall, the combined application of MLE and SA could be used for alleviating the adverse effects of growth, physiology, yield criteria and WUE in drought-stressed maize plants.     

Improvement in the Adaptation of Lygeum Spartum L. to Salinity In the Presence of Calcium

Lygeum spartum L. has been recently introduced in areas where salinity is high in soils. However, there are no studies about the physiological response of these plants to salt excess. The effect of sodium chloride (NaCl) on plant growth and water status was studied. Also, the effect of calcium (Ca) addition to salinity conditions was analyzed because of the coexistence of salinity and calcareous soils. Dry weight (DW), transpiration, and osmotic potential (Ψπ) decreased with elevated NaCl and were restored with Ca²⁺, whereas moderate salinity had no effect. Fresh weight (FW), water potential (Ψω), and root hydraulic conductance (L ₀) decreased with salinity; Ca²⁺ supply had an ameliorative effect at moderate salinity. Sodium (Na⁺) increased in leaf sap at high levels of NaCl and was decreased by Ca²⁺. Lygeum spartum showed a resistance to moderate salinity, but the effect of Ca²⁺ depends on salinity intensity. Thus, the role of Ca²⁺ in the tolerance to salinity was emphasized.     

CHARACTERIZATION OF THE PHYSIOLOGICAL RESPONSE OF THE HIGHLY-TOLERANT TOMATO CV. ‘PONCHO NEGRO’ TO SALINITY AND EXCESS BORON

The variety of tomato (Solanum lycopersicum) called ‘Poncho Negro’ by farmers represents an important source of genetic resources of agricultural interest, because it has managed to thrive at levels of salinity and excess B that other varieties of the same species find impossible. This work was conducted under controlled growth conditions in a greenhouse, evaluating and obtaining plant material that served for physiological, chemical, and biochemical determinations. Stress conditions were supplied by irrigation, using different concentrations of sodium chloride (NaCl; 75 and 150 mM) and excess boron (B; 5 and 20 mg L^?1). The rate of net carbon dioxide (CO₂) assimilation, the quantum efficiency of photosynthesis and the relative water content (RWC) were measured. In addition, B, sodium (Na⁺), potassium (K⁺), and calcium (Ca²⁺), soluble sugars, and proline were quantified. The results suggest that ‘Poncho Negro’ accumulated Na⁺ mainly in the roots, partly limiting its entry into the aerial parts. In addition, it should be noted that the interaction of B and salinity reduced the movement of Na⁺ to the leaves. The ability of cv. ‘Poncho Negro’ to minimize leaf Na⁺ accumulation, accumulate more leaf B than control plants, and maintain its K⁺ level, when grown with an excess of B, possibly allowed the observed increase in the rate of photosynthesis. In addition, these tomato plants used proline and soluble sugars as osmo-regulators under high-B and saline conditions. Under all stress conditions studied, this variety of tomato was able to regulate its water content, with RWC values of approximately 86%.     

Regulation of xylem transport of calcium from roots to shoot of maize by growth-related demand

The aim of the present experiments was to study the effect of growth-related nutrient demand on Ca²⁺ translocation from roots to shoot of maize (Zea mays L.). The plants were grown under controlled environmental conditions in nutrient solution with constant Ca²⁺ supply. The growth-related demand for Ca²⁺ and other nutrients was modified by growing the plants with their apical shoot meristem either at air temperature (24°C/20°C day/night) or at 14°C. Reduction of the shoot meristem temperature (SMT) to 14°C decreased shoot growth without affecting root growth in the first five days, which diminished the growth-related demand of the shoot for nutrients per unit of roots. This decrease in shoot demand led to a reduction not only of Ca²⁺ translocation rates in intact transpiring plants but also of Ca²⁺ fluxes in the xylem exudate of decapitated plants. This indicates that the decrease in xylem flux of Ca²⁺ at low SMT was not only the result of low transpiration-related water flux, and thus possibly low apoplasmic bypass transport of Ca²⁺ into the stele. In decapitated plants precultured at low SMT, the water flux through the roots was diminished even more than Ca²⁺ flux, leading to a significant increase in the Ca²⁺ concentration of the exudate, and thus presumably an increase in the Ca²⁺ gradient between cytosol and apoplast of stelar parenchyma cells. When the osmotically driven water flux was reduced by addition of mannitol to the nutrient solution, Ca²⁺ concentration in the exudate markedly increased, whereas Ca²⁺ translocation was only slightly affected. From these results it is suggested that the decrease in Ca²⁺ translocation rates at low shoot demand was not related to low water flux but to direct effects on the capacity of Ca²⁺ transport mechanisms in the roots.     

Chromium Alters Iron Nutrition and Water Relations of Spinach

Spinach (Spinacea oleracea L. cv. ‘Banarasi’), known to be responsive to potentially toxic elements, was investigated for chromium (Cr^{6 +}) effect on iron metabolism and water relations. After 40 days growth in sand culture, a set of plants was supplied with 100 and 400 μM Cr^{6 +} (potassium dichromate, K₂Cr₂O₇), superimposed over the complete nutrient solution (control). Excess Cr^{6 +} produced visual symptoms of toxicity and increased accumulation of Cr, more in roots than in leaves. Decreased concentration of chlorophylls and the activities of heme enzymes, catalase and peroxidase in excess Cr^{6 +} may suggest interference of Cr in iron metabolism of plants. These changes associated with decrease in iron (Fe) accumulation in Cr^{6 +} treated plants, indicate that by reducing absorption of Fe, Cr^{6 +} impairs the Fe requiring steps of chlorophyll and heme biosynthesis. In spite of lower water saturation deficit, the leaves of Cr^{6 +} treated plants showed a decrease in leaf water potential, associated with increase in diffusive resistance and lowering of transpiration rate along with proline accumulation indicates water stress. The changes observed in water stress parameters in Cr^{6 +} treated plants indicate that excess supply of Cr^{6 +} reduces the physiological availability of water.     

Effect of Calcium and Potassium Nutrition on Yield,Ion Content,and Salt Tolerance of Brassica campestris (rapa)

When plants encounter salinity, growth is reduced initially by water stress and subsequently by toxic levels of ions and by interference with nutrient acquisition and translocation. Calcium (Ca^{2 +}) in particular seems to have an important role in salt tolerance and there are reports of a beneficial effect of increasing Ca^{2 +} availability. Higher potassium (K⁺) concentrations in plants may also improve salinity tolerance as sodium (Na)⁺/K⁺ ratios have been shown to be important. Previous work with a range of Acacia species has suggested that endogenous seed Ca^{2 +} and K⁺ concentrations might influence salinity tolerance at germination, but this has not previously been tested with a single species. The objectives of this investigation were thus to determine whether (1) altered Ca^{2 +} and K⁺ nutrition of Brassica campestris (rapa) L. plants affects the yield and ion content of their seeds, and (2) seeds with different Ca^{2 +} and K⁺ contents differ in their salinity tolerance. Plants were grown in a growth room or greenhouse in (1) Gem® horticultural sand (2) Silvaperl® perlite and sand (2:1), or (3) Shamrock® Medium General Purpose Irish Sphagnum Peat and Vermiperl® vermiculite (1:1). Plants in each growth substrate were supplied with nutrient solutions based on a modified Hoagland's solution as a control, low Ca^{2 +} and low K⁺ solutions containing those elements at half the control strength, but all other mineral elements as far as possible at control strength, and high Ca^{2 +} and high K⁺ solutions containing those elements at double control strength but all other mineral elements, as far as possible, at control strength. An increase in substrate available Ca^{2 +} and K⁺ resulted in increased Ca^{2 +} and K⁺ concentration in seeds, respectively, and was accompanied by a reduction in seed K⁺ and Ca^{2 +}, respectively. The Ca^{2 +} and K⁺ concentrations of seeds affected their salinity tolerance. Increases in seed Ca^{2 +}, K⁺ or Ca^{2 +}+ K⁺ concentrations decreased salinity tolerance at germination. The results, especially in terms of Ca^{2 +} nutrition, contradict previous results of an increased salinity tolerance with increased Ca^{2 +} and/or K⁺ concentrations.     

Effects of aluminium on growth and nutrition in birch seedlings under magnesium- or calcium-limiting growth conditions

Growth and nutrition of birch seedlings (Betula pendula Roth) with and without 0.5 mM Al³⁺ were studied. The seedlings were cultivated at growth-limiting Mg- or Ca-conditions by adding one of these elements at relative addition rates (R_Mg, R_Ca) of 0.15 day^?1. The concentration of Ca²⁺ in the Mg-limited treatments was 0.01.0.1 or 1 mM and Mg²⁺ was given in equal molarities in the Ca-limited treatments. The relative growth rates, R_G, of the plants and plant parts attained values close to R_Mg or R_Ca and were not affected by the concentration of Ca²⁺, Mg²⁺ or Al³⁺ in the culture solution. Uptake of Ca, at Ca-limitation, increased significantly in the roots after addition of Al, and decreased in all plant parts when the Mg concentration of the culture solution was raised. Less clear effects were found on Mg uptake at Mg-limitation. The inhibitory effect of Al on Mg uptake decreased with time as a result of the growth technique. The root mass fraction was significantly larger in plants limited in Ca (24%) than in plants limited in Mg (20%). The usefulness in using the balance between Ca and Al or ratios between Ca, Mg, K and Al as diagnostic tools for assessing the nutritional status of trees is discussed.     

Salt Stress Induces Accumulation of γ–Aminobutyric Acid in Germinated Foxtail Millet (Setaria italica L.)

Effects of NaCl treatments on sprout length, the contents of soluble protein, free amino acids, and γ‐aminobutyric acid (GABA) and on glutamate decarboxylase (GAD) activity in germinated foxtail millet were investigated, and the regulating effects of exogenous Ca²⁺, along with lanthanum chloride (LaCl₃, a specific inhibitor of the Ca²⁺ pathway) and ethylene glycol tetraacetic acid (EGTA, a chelator of Ca²⁺) under salt stress, on GABA accumulation in germinated millet were examined in this paper. The results showed that NaCl treatments caused a decrease in sprout length of millet. Low concentration of NaCl treatments increased soluble protein content, but high concentration decreased soluble protein content. The level of free amino acids, GAD activity, and GABA content increased significantly under NaCl stress. Exogenous Ca²⁺ application under NaCl stress further increased GAD activity and GABA content; the optimal concentration of Ca²⁺ for GAD activity and GABA accumulation was 5.0mM under 100mM NaCl for 48 hr, at which GABA content was 31.92 mg/100 g, a 1.41‐fold increase as compared with that in seeds under NaCl stress (22.64 mg/100 g). GAD activity and GABA accumulation in germinated millet decreased when treated with LaCl₃ or EGTA under NaCl stress. Our results suggest that salt stress combined with Ca²⁺ treatment may be used for preparation of millet with higher GABA content, which can be used as a natural resource for functional foods.     

Ethylene evolution and ammonium accumulation by tomato plants under water and salinity stresses. Part II

Foliar wilting, epinasty, abscission, chlorosis, and necrosis are common symptoms in plants affected by water and salinity stresses. Ethylene evolution and ammonium accumulation frequently accompany the expression of the symptoms of stresses from various origins. These symptoms and physiological phenomena have been associated with other environmental stresses, such as ammonium toxicity. Intact and excised tomato plants (Lycopersicon esculentum Mill. ‘Heinz 1350’ and neglecta‐1) were subjected to stresses of waterlogging, water‐deficit, or saline conditions (NaCl or CaCl₂). In soil culture in the greenhouse, tomato plants subjected to waterlogging developed epinasty and chlorosis and had increased ethylene evolution and ammonium accumulation. The application of aminooxyacetic acid (AOA) ameliorated the symptoms and reduced ethylene evolution and ammonium accumulation. Tomato subjected to drought developed chlorosis and had enhanced ammonium accumulation, but no increased ethylene evolution was observed. The chlorotic and necrotic symptoms were observed for plants receiving NaCl or CaCl₂. Application of ammonium nutrition or water stress aggravated the development of toxic symptoms. Ammonium accumulation and ethylene evolution were enhanced with intact plants or excised seedlings under these stresses. Application of AOA through stems of excised seedlings suppressed the enhancement. ‘Heinz 1350’ receiving CaCl₂ accumulated more Ca⁺⁺ and had higher ethylene evolution than those receiving NaCl or the neglecta‐1 receiving CaCl₂. Neglecta‐1 accumulated more Na⁺ with the NaCl treatment and had higher ethylene evolution than ‘Heinz 1350’. The results indicate that environmental stresses stimulate ammonium accumulation and initiate ethylene evolution, which may function in development of stress induced symptoms.     

Effects of Multiple Reference Plants,Season, and Irrigation on Biological Nitrogen Fixation by Pasture Legumes using the Isotope Dilution Method

Abstract

The popular and widely used ¹⁵nitrogen (N)–isotope dilution method for estimating biological N fixation (BNF) of pasture and tree legumes relies largely on the ability to overcome the principal source of error due to the problem of selecting appropriate reference plants. A field experiment was conducted to evaluate the suitability of 12 non‐N₂‐fixing plants (i.e., nonlegumes) as reference plants for estimating the BNF of three pasture legumes (white clover, Trifolium repens L.; lucerne, Medicago sativa; and red clover, Trifolium pratense L.) in standard ryegrass–white clover (RWC) and multispecies pastures (MSP) under dry‐land and irrigation systems, over four seasons in Canterbury, New Zealand. The ¹⁵N‐isotope dilution method involving field ¹⁵N‐microplots was used to estimate BNF. Non‐N₂‐fixing plants were used either singly or in combination as reference plants to estimate the BNF of the three legumes. Results obtained showed that, on the whole, ¹⁵N‐enrichment values of legumes and nonlegumes varied significantly according to plant species, season, and irrigation. Grasses and herb species showed higher ¹⁵N‐enrichment than those of legumes. Highest ¹⁵N‐enrichment values of all plants occurred during late summer under dry‐land and irrigation conditions. Based on single or combined non‐N₂‐fixing plants as reference plants, the proportion of N derived from the atmosphere (% Ndfa) values were high (50 to 90%) and differed between most reference plants in the MSP pastures, especially chicory (Cichorium intybus), probably because it is different in phenology, rooting depth, and N‐uptake patterns compared to those of legumes. The percent Ndfa values of all plants studied also varied according to plant species, season, and irrigation in the MSP pastures. Estimated daily amounts of BNF varied according to pasture type, time of plant harvest, and irrigation, similar to those shown by percent Ndfa results as expected. Irrigation increased daily BNF more than 10‐fold, probably due to increased dry‐matter yield of pasture under irrigation compared to dry‐land conditions. Seasonal and irrigation effects were more important in affecting estimates of legume BNF than those due to the appropriate matching of N₂‐fixing and non‐N₂‐fixing reference plants.     

COMPARISON OF OSMOTIC REGULATION IN DEHYDRATION- AND SALINITY-STRESSED SUNFLOWER SEEDLINGS

Plant dry matter accumulation rate (DMAR), relative water content (RWC), electrolyte leakage percentage (ELP), chlorophyll content, osmotic adjustment ability (OAA), and osmotica accumulation in leaves of sunflower (Helianthus annuus L.) seedlings under different levels of dehydration and salinity stress induced by iso-osmotic PEG (polyethylene glycol) or sodium chloride (NaCl) were evaluated. Plants were subjected to four stress treatments for 10 days: ?0.44 MPa PEG6000, ?0.44 MPa NaCl, ?0.88 MPa PEG6000, ?0.88 MPa NaCl. Results showed that PEG and NaCl treatments decreased the plant's DMAR and RWC, and NaCl treatments had more severe inhibitory effect on the plants than PEG treatments. Leaf ELP in sunflower seedlings increased after NaCl and PEG treatments. However, leaf ELP under salt stress was higher than that under dehydration stress (PEG treatment). All stress treatments increased OAA in plant leaves. Leaf OAA was enhanced significantly as PEG concentration increases, while leaf OAA was less enhanced at higher concentration of NaCl. OAA of sunflower leaves under dehydration stress was due to an increase in potassium (K⁺), calcium (Ca²⁺), amino acid, organic acid, magnesium (Mg²⁺), and proline content. OAA of sunflower leaves under moderate salt stress was owing to an increase in K⁺, chlorine (Cl^?), amino acid, organic acid, sodium (Na⁺), and proline content, and was mainly due to an accumulation of K⁺, Cl^?, Na⁺, and proline under severe salt stress.     

Impact of a biochar or a biochar-compost mixture on water relation, nutrient uptake and photosynthesis of Phragmites karka

Soil water and nutrient status are both of major importance for plant appearance and growth performance. The objective of this study was to understand the effect of biochar (1.5%) and a biochar-compost mixture (1.5% biochar + 1.5% compost) on the performance of Phragmites karka plants grown on a synthetic nutrient-poor sandy clay soil (50% sand, 30% clay, and 20% gravel). Indicators of plant performance, such as growth, lignocellulosic biomass, water status (leaf water potential, osmotic potential, and turgor potential), mineral nutrition status, leaf gas exchange, and chlorophyll fluorescence, and soil respiration (carbon dioxide (CO₂) flux) were assessed under greenhouse conditions. Biochar-treated plants had higher growth rates and lignocellulosic biomass production than control plants with no biochar and no compost. There was also a significant increase in soil respiration in the treatments with biochar, which stimulated microbial interactions. The increase in soil water-holding capacity after biochar amendment caused significant improvements in plant water status and plant ion (K⁺, Mg²⁺, and Ca²⁺) contents, leading to an increase in net photosynthesis and a higher energy-use efficiency of photosystem II. Biochar-treated plants had lower oxidative stress, increased water-use efficiency, and decreased soil respiration, and the biochar-compost mixture resulted in even greater improvements in growth, leaf turgor potential, photosynthesis, nutrient content, and soil gas exchange. Our results suggest that biochar and compost promote plant growth with respect to nutrient uptake, water balance, and photosynthetic system efficiency. In summary, both the soil amendments studied could increase opportunities for P. karka to sequester CO₂ and produce more fodder bio-active compounds and biomass for bio-energy on nutrient-poor degraded soils.     

Bioremediation of heavy metals from municipal sewage by cyanobacteria and its effects on growth and some metabolites of Beta vulgaris

The present research was done to study the ability of cyanobacterial species for removing heavy metals from sewage. As well, to estimate the growth and some metabolites of Beta vulgaris irrigated with sewage treated by cyanobacterial species. The best removal results were obtained by Anabaena oryzae compared to the other studied cyanobacteria. Whereas A. oryzae showed high removal efficiency for cadmium (Cd²⁺) followed by lead (Pb²⁺), zinc (Zn²⁺), iron (Fe²⁺), copper (Cu²⁺) and manganese (Mn²⁺) (88.5, 83.1, 68.8, 62.0, 55.2 and 42.4%, respectively). Irrigation of plants by untreated or treated sewage generally caused stimulation in the total proteins, proline, carbohydrates and ascorbic acid. B. vulgaris grown in soil irrigated with untreated sewage showed maximum catalase, peroxidase activity, hydrogen peroxide (H₂O₂) and lipid peroxidation compared to the other treatments. The heavy metals availability was relatively low in the plant irrigated with treated sewage by cyanobacterial species, so the antioxidants requirement was low and hence the induction of antioxidants was lower compared to the plant irrigated with untreated sewage.     

Effects of biofertilizers and cycocel on some physiological and biochemical traits of wheat (Triticum aestivum L.) under salinity stress

In order to study the effects of biofertilizers and cycocel on some physiological and biochemical characteristics of wheat (Triticum aestivum L.) under salinity condition, a factorial experiment was conducted based on randomized complete block design with three replications under greenhouse condition in 2015. Treatments were included salinity in four levels [no salt (control or S₀), salinity 30 (S₁), 60 (S₂) and 90 (S₃) mM NaCl equivalent of 2.76, 5.53 and 8.3 dS m^?1, respectively], four biofertilizers levels [no biofertilizer (F₀), seed inoculation by Azotobacter chrocoocum strain 5 (F₁), Pseudomonas putida strain 186 (F₂), both inoculation Azotobacter + Pseudomonas (F₃)] and three cycocel levels [without cycocel as control (C₀), application of 600 (C₁) and 1000 (C₂) mg L^?1]. Results showed that salinity severe stress (90 mM) decreased chlorophyll content, relative water content (RWC), total chlorophyll, photochemical efficiency of PSII and yield of wheat. Whereas, soluble sugars and proline content, electrical conductivity (EC), the activity of catalase (CAT), peroxidase (POD), polyphenol oxidase (PPO) enzymes were increased. Similar results were observed in CAT, POD and PPO activities due to inoculation by biofertilizers and cycocel. Salinity at 30 mM increased the photochemical efficiency of PSII and chlorophyll content in plants grown under biofertilizer and cycocel treatment but with increasing salinity up to 90 mM mentioned parameters were decreased. The highest proline and soluble carbohydrate at all salinity levels were observed in plants treated in the highest cycocel level and Azotobacter+ Pseudomonas application. Generally, it was concluded that biofertilizers and cycocel can be used as a proper tool for increasing wheat yield under salinity condition.     

Responses of Batis maritima plants challenged with up to two‐fold seawater NaCl salinity

Batis maritima is a promising halophyte for sand‐dune stabilization and saline‐soil reclamation. This species has also applications in herbal medicine and as an oilseed crop. Here, we address the plant response to salinity reaching up to two‐fold seawater concentration (0–1000 mM NaCl), with a particular emphasis on growth, water status, mineral nutrition, proline content, and photosystem II integrity. Plant biomass production was maximal at 200 mM NaCl, and the plants survived even when challenged with 1000 mM NaCl. Plant water status was not impaired by the high accumulation of sodium in shoots, suggesting that Na⁺ compartmentalization efficiently took place in vacuoles. Concentrations of Mg²⁺ and K⁺ in shoots were markedly lower in salt‐treated plants, while that of Ca²⁺ was less affected. Soluble‐sugar and chlorophyll concentrations were hardly affected by salinity, whereas proline concentration increased significantly in shoots of salt‐treated plants. Maximum quantum efficiency (F_v/F_m), quantum yield of PSII (Φ_PSII), and electron‐transport rate (ETR) were maximal at 200–300 mM NaCl. Both nonphotochemical quenching (NPQ) and photochemical quenching (qP) were salt‐independent. Interestingly, transferring the plants previously challenged with supraoptimal salinities (400–1000 mM NaCl) to the optimal salinity (200 mM NaCl) substantially restored their growth activity. Altogether, our results indicate that B. maritima is an obligate halophyte, requiring high salt concentrations for optimal growth, and surviving long‐term extreme salinity. Such a performance could be ascribed to the plant capability to use sodium for osmotic adjustment, selective absorption of K⁺ over Na⁺ in concomitance with the stability of PSII functioning, and the absence of photosynthetic pigment degradation.     

Effects of Ca,Mg, K,Na, and pH on Copper Toxicity to Pakchoi (Brassica chinensis L.)

The influence of calcium, magnesium, sodium, and potassium (Ca²⁺, Mg²⁺, Na⁺, K⁺) ions and pH on copper (Cu) toxicity to pakchoi (Brassica chinensis L.) was independently estimated by measuring root elongation in nutrient solutions. Increases in Ca²⁺, Mg²⁺, and hydrogen (H⁺) significantly increased the 5-d EC50Cu_T (expressed as total soluble Cu) by a factor of 12 for all treatments, which clearly demonstrated the limitation of using total Cu concentration to predict Cu toxicity to pakchoi. EC50{Cu²⁺} (expressed as free Cu²⁺ activity) was not significantly influenced by changing the Ca²⁺, Mg²⁺, and H⁺ activities. The nonlinear relationship between EC50{Cu²⁺} and cations indicated that competition for binding sites between Cu²⁺ and cations was not a significant factor in determining toxicity of Cu²⁺ for pakchoi. The lower variation of EC50{Cu²⁺} suggests that free Cu²⁺ activity was a better predictor of toxicity to pakchoi than EC50Cu_T.