Invertase activity limits grain yield of maize under salt stress

Salt stress reduces grain yield of maize (Zea mays L.) due to poor kernel setting but not due to decreased grain filling. In the present study, it was tested whether acid invertase activity is decreased in developing kernels of maize under salt stress, and if assimilate supply is limited. The relatively salt‐sensitive maize hybrid Pioneer 3906 was compared with the more salt‐resistant hybrid SR 12. Salt stress caused a significant decrease in grain yield which was due to a 50% decrease in kernel number. No source limitation was observed, as the sucrose concentrations in kernels were significantly increased under salt stress for both genotypes. In contrast, glucose and fructose concentrations in kernels were significantly decreased. Salt stress caused a significant inhibition of soluble acid invertase activity to 19% in hydroponics 5 d after pollination (5 DAP) and to 50% in the soil culture experiment (2 DAP). The decrease in enzyme activity was the same for both genotypes. In the soil experiment, the highest soluble acid invertase activity was found 2 DAP with a steep decline until 8 DAP in Pioneer 3906. It is concluded that a decrease in acid invertase activity is a key factor associated with limited kernel setting under salt stress but additional factors may be responsible for genotypic differences.     

Effect of phosphogypsum application and bacteria co-inoculation on biochemical properties and nutrient availability to maize plants in a saline soil

Phosphogypsum (PG), which contains Ca, P and S and has an acidic effect, may be applied to manage soil constraints such as alkalinity and salinity. For increasing nutrients bioavailability, biofertilizers are commonly applied. Therefore, the aim of this study was to assess PG effect either alone or in combination with the mixed co-inoculation of plant growth promoting rhizobacteria on a saline soil. In a greenhouse pot experiment with maize (Zea mays L.), the inoculated and non-inoculated saline soils were treated with PG at 10 g kg^?1 (PG10), 30 g kg^?1 (PG30), and 50 g kg^?1 (PG50). The soil pH, electrical conductivity (EC_e), and macro-(NPK) and micronutrients (Fe, Mn, Zn, and Cu) availability to mays were examined. Applying PG reduced soil pH and co-inoculation induced significant decreases in soil EC_e. Applying PG increased significantly soil available P. Applying PG combined with co-inoculation effectively increased the soil available K. The soil available micronutrients decreased significantly with PG. However, the inoculated maize treated with PG showed significant higher dry weight (82.1–127.4%) and nutrients uptake than the control. It could be concluded that PG along with co-inoculation may be an important approach for alleviating negative effects of salinity on plant growth.     

Comparison of nutrient uptake and antioxidative response among four Labiatae herb species under salt stress condition

Herbs of the Labiatae have relatively low salt tolerance. They are widely grown in drylands, but salt stress there is a typical problem and may reduce yields. To examine their salt tolerance mechanisms, we grew basil, sage, thyme, and oregano in nutrient solution containing 50 mM NaCl and determined the biomass; contents of Na, K, and Mg in leaf blades, stems, and roots; contents of total chlorophyll, malondialdehyde (MDA), hydrogen peroxide in leaf blades; and activities of antioxidative enzymes in leaf blades. The salt tolerance decreased in the order of basil ≈ sage > thyme > oregano. The good salt tolerance of basil was explained by a significant increase in the activity of catalase, in addition to the low Na/K ratio of leaf blades due to the retention of Na in stems and roots and of K in leaf blades. The good salt tolerance of sage was explained by the low Na/K ratio in leaf blades and the prevention of lipid peroxidation by high antioxidative enzyme activities, despite its poorer management of nutrient uptake. In thyme, although catalase activity increased significantly to alleviate salt-induced oxidative stress caused by Na influx into all parts, low K and Mg allowed shoot weight in particular to decrease. In oregano, antioxidative responses appeared as significant increases in ascorbate peroxidase and glutathione reductase activity, and K was accumulated in leaf blades, but serious salt-induced oxidative stress caused by high Na influx into all parts reduced the growth of all parts. These results show that despite similar responses among species, salt tolerance is not necessarily the same. In this experiment, we revealed the salt tolerance mechanism of each of four Labiatae herbs by revealing their strengths and weaknesses in nutrient uptake and antioxidative responses.     

Grain filling and yield of mung bean affected by salicylic acid and silicon under salt stress

Two experiments were carried out in 2013 and 2014, to investigate changes in grain filling rate (GFR), grain filling duration (GFD) and yield of mung bean in response to salicylic acid (SA) and silicon (Si) under salt stress (0, 3, 6 and 9 dS m^?1). In experiment 1, four levels of SA (0, 0.5, 1 and 1.5 mM), but in experiment 2, two levels of SA (0 and 1 mM) and Si (0 and 2 mM) were applied. In experiment 1, GFR, GFD, yield components, biological and grain yields and harvest index were decreased with increasing salt stress. Application of different levels of SA, especially 1 mM, increased GFR, but decreased GFD. In experiment 2, GFD under salinity was shorter than that under non-saline condition, resulting in comparatively smaller grains. Application of Si and particularly SA accelerated grain development under all salinity treatments. The superiority of SA treated plants in GFR, grain weight and grains per plant resulted in greater grain yield per plant under saline and non-saline conditions.     

Silicon effect on growth,nutrient uptake,and yield of peanut (Arachis hypogaea L.) under aluminum stress

Abstract

The objective of this study was to investigate the effect of silicon (Si) on growth, nutrient uptake, and yield of peanut under aluminum (Al) stress. Peanut (Arachis hypogaea L. cv. Zhonghua 4) raised with or without Si (1.5?mM) in the growth chamber under 0 and toxic Al (0.3?mM) levels. Aluminum stress significantly decreased the biomass and root dry weight by 12.9% and 10.7%, and the pod yield, number of mature pod per plant and seed number of per pod by 16.7%, 10.7%, and 13.9%. The content of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) was significantly decreased, but that of Al increased markedly in shoots and roots of peanut after Al exposure at seedling, flower-needle and pod-setting stage. Under Al stress condition, Si application protected peanut by improving nutrient uptake at different growth stages and favoring the partitioning of dry mass to pod and the allocation of tissue N, P, K, Ca, and Mg to shoots and pod and decreasing Al uptake and accumulation.     

Silicon modulates the activity of antioxidant enzymes and nitrogen compounds in sunflower plants under salt stress

Sunflower (Helianthus annuus L.) is an important oilseed crop with clear sensibility to salt stress. In this study, we evaluated silicon (Si) effect on the nitrogen metabolism and antioxidant enzyme activity in sunflower plants subjected to salinity. A 4 × 4 factorial arrangement of treatments in a completely randomized design with four replicates was used, consisting of four concentrations of Si (0.0; 1.0; 1.5; and 2.0 mM) and four concentrations of NaCl (0; 50; 100; and 150 mM) in the nutrient solution. The salinity reduced the nitrate content, but the increasing Si concentration in the medium improved the nitrate uptake, leading this ion to accumulate in salt-stressed plants, particularly in the roots. The nitrate reductase activity and the proline and soluble N-amino contents were also significantly increased by Si in salt conditions. The salinity increased electrolyte leakage and reduced the activity of enzymes superoxide dismutase, ascorbate peroxidase and catalase in sunflower plants, but these decreases were reversed by Si at 2 mM, thus alleviating the effects of salinity on these variables. We conclude that Si is able to positively modulate nitrogen metabolism and antioxidant enzyme activities in sunflower plants in order to alleviate the harmful effects of salinity.     

Decline in leaf growth under salt stress is due to an inhibition of H+‐pumping activity and increase in apoplastic pH of maize leaves

In this study, salt‐induced changes in the growth rate of maize (Zea mays L.) were investigated during the first phase of salt stress. Leaf growth was reduced in the presence of 100 mM NaCl, and effects were more pronounced for the salt‐sensitive cv. Pioneer 3906 in comparison to the hybrid SR03. While hydrolytic activity of plasma membrane remained unaffected, H⁺‐pumping activity was reduced by 47% in Pioneer 3906, but was unchanged in SR03. Changes in apoplastic pH were detected by ratiometric fluorescence microscopy using the fluorescent dye fluorescein isothiocyanate‐dextran (50 mM). Pioneer 3906 responded with an increase of 0.2 pH units in contrast to SR03 for which no apoplastic alkalization was found. With respect to the hypothesis that the apoplastic pH is influenced by salinity, it is suggested that salt resistance is partly achieved due to efficient H⁺‐ATPase proton pumping, which results in cell‐wall acidification and loosening.     

硅促进盐胁迫下黄瓜NHX1基因表达及Na+在液泡中的区隔化效应

  【目的】   硅可提高植物的耐盐性,但不同植物中硅提高耐盐性的机理并不相同。探究硅对盐胁迫下黄瓜幼苗的氧化损伤、Na+积累和激素水平的影响,以阐明硅提高黄瓜耐盐性的机制。   【方法】   以基因型为Mch-4的黄瓜幼苗为试材,进行水培试验。营养液中NaCl的胁迫浓度为65 mmol/L,施硅水平为Na₂SiO₃·9H₂O 0.3 mmol/L。在处理10天后,测定黄瓜幼苗生物量、Na+含量与分配、Na+转运相关基因表达水平及激素含量。   【结果】   施硅可改善盐胁迫下黄瓜幼苗的生长,减轻植株的氧化损伤。硅对盐胁迫下黄瓜根系和叶片Na+含量无明显影响,可显著降低根和叶中质膜Na+/H+反向转运蛋白基因SOS1的表达量,对高亲和力钾转运蛋白基因HKT1的表达均影响不大,但促进了液泡膜Na+/H+反向转运蛋白基因NHX1的表达。对盐胁迫下黄瓜叶片Na+的亚细胞定位发现,硅处理使叶绿体中Na+含量下降,而液泡中Na+含量升高。硅处理提高了盐胁迫植株根和叶片中赤霉素、生长素和细胞分裂素的水平。   【结论】   施硅可提高液泡膜Na+/H+反向转运蛋白基因NHX1的表达,将Na+区隔化于液泡中,进而降低叶绿体中的Na+含量,缓解盐胁迫下黄瓜幼苗的氧化损伤;硅还诱导产生了较多的赤霉素、生长素和细胞分裂素,其调控Na+积累和黄瓜幼苗的氧化损伤的机理还需进一步研究。     

Response of wheat genotypes to foliar spray of ZnO and Fe2O3 nanoparticles under salt stress

This study evaluated the effects of iron oxide (Fe₂O₃) and zinc oxide (ZnO) on two wheat genotypes (Kavir and Tajan) at three levels (0, 75, and 150 mM sodium chloride (NaCl)) of salinity. Spray treatments included two forms of normal and nanoparticles of Fe₂O₃ and ZnO, a mixture of nanoparticles of Fe₂O₃ and ZnO (2 g L^?1) and a non-spray treatment. The pot experiment was arranged as factorial in a randomized complete block design with four replications. Two forms of Fe₂O₃ and ZnO significantly accelerated plant height, leaf area, shoot dry weight, and the concentration of iron (Fe) and zinc (Zn) in comparison with non-spray treatment. The highest plant height and leaf Fe concentration belonged to Fe₂O₃ nanoparticles; however, it seems that the spray of nanoparticles may not be superior compared with normal forms in alleviation of salinity impacts.     

Optimization of irrigation and nutrient concentration based on economic returns,substrate salt accumulation and water use efficiency for tomato in greenhouse

To evaluate the effects of different irrigation and nutrient concentration strategy on growth, yield, water use efficiency (WUE), fruit quality and substrate salt accumulation, tomatoes were grown with five different levels of water (W: 50%, 75%, 100%, 125% and 150%) and nutrient concentrations (N: 0.5, 0.75, 1.0, 1.5 and 2.0 times of Hoagland strength(X)). Fruit quality index was determined by normalization of fruit quality parameters. Deficit irrigation at standard concentration of nutrients reduced yields by 17.43% and 15.52% for T₇ (W_75%-N_1.0x) and 49.54%–51.99% for T₈ (W_50%-N_1.0x) during spring-summer (SS) and fall-winter (FW) seasons, respectively. Contents of total soluble solids (TSS), titrable acidity (TA) and sugar acid ratio (SAR) were all increased in water-deficit treatments. T₈ was found to be highest in TSS, TA and SAR except SAR in FW. Over-irrigation with excessive and standard Hoagland nutrient concentration caused non-significant reduction in yield except T₆ (W_125%-N_1.0x) in SS. T₂ (W_100%-N_2.0x) and T₄ (W_100%-N_1.5x) caused more substrate salt accumulation which resulted in significant decrease in yield and WUE. Through economic analysis, over-watering along with excessive nutrients caused profit reductions. Considering water saving, yield and fruit quality through economic analysis, T₇ found to be optimal strategy.     

Simulating NaCl accumulation in a closed hydroponic crop of zucchini: Impact on macronutrient uptake,growth, yield,and photosynthesis

Zucchini squash (Cucurbita pepo L.) plants were grown in a closed‐loop hydroponic system and supplied with nutrient solution (NS) containing NaCl at different concentrations (0.7, 3, 5, and 7 mM). The primary aim of the study was to define the relationship between the concentration of Na⁺ and Cl⁻ in the root zone solution and the respective Na⁺/water or Cl⁻/water uptake ratios (uptake concentrations, UC). A second objective was to determine the UC of macronutrients (i.e ., N, P, K, Ca, and Mg) and to test whether they are influenced by the gradual increase of the root zone salinity due to progressive NaCl accumulation. Two experiments were conducted, of which one (spring crop) was used to parameterize an existing empirical model, while the second one (autumn‐winter crop) was commissioned to test the validity of the determined model parameters. Both Cl⁻ and Na⁺ ions accumulated progressively in the root zone solution over time, showing a tendency to stabilize at final concentrations according to the corresponding NaCl treatment. The relationship between the Na⁺ and Cl⁻ concentrations in the root zone and the Na⁺/water or Cl⁻/water uptake ratios was exponential and the model parameters successfully fitted to data from crops cultivated in different growth seasons. This model may be used to monitor Na⁺ and Cl⁻ concentrations in the root environment of zucchini crops as relationships of the plant water consumption. The exposure of plants to NaCl affected the UC of N, K, Ca, and Mg, but the results for some nutrients were not consistent in both growth seasons. The measurements of plant growth characteristics (i.e ., biomass, yield, fruit quality, and photosynthesis) revealed that water resources containing up to 3 mM NaCl do not cause unacceptable yield losses in zucchini crops grown in completely closed hydroponic systems.     

Utilization index: A modified approach to the estimation and comparison of nutrient utilization efficiency in plants

The disadvantages of using utilization quotient (biomass per unit amount of nutrient present in biomass) in comparing nutrient utilization efficiencies of different varieties and species are discussed. A modified approach to the estimation of utilization efficiency is presented. A comparison of efficiencies of two plants calculated by this method gives an index which is the ratio of biomass ratio: tissue nutrient concentration ratio. Theoretical validity and advantages in practical application of this approach are discussed.     

Inoculation of tomato plants with selected PGPR represents a feasible alternative to chemical fertilization under salt stress

Plant growth‐promoting rhizobacteria (PGPR) are soil bacteria that colonize the rhizosphere of plants, enhance plant growth, and may alleviate environmental stress, thus constituting a powerful tool in sustainable agriculture. Here, we compared the capacity of chemical fertilization to selected PGPR strains to promote growth and alleviate salinity stress in tomato plants (Solanum lycopersicum L.). A pot experiment was designed with two main factors: fertilization (chemical fertilization, bacterial inoculation with seven PGPR, or a non‐fertilized non‐inoculated control) and salt stress (0 or 100 mM NaCl). In the absence of stress, a clear promotion of growth, a positive effect on plant physiology (elevated F_v/F_m), and enhanced N, P, and K concentrations were observed in inoculated plants compared to non‐fertilized controls. Salinity negatively affected most variables analyzed, but inoculation with certain strains reduced some of the negative effects on growth parameters and plant physiology (water loss and K⁺ depletion) in a moderate but significant manner. Chemical fertilization clearly exceeded the positive effects of inoculation under non‐stressed conditions, but conversely, biofertilization with some strains outperformed chemical fertilization under salt stress. The results point at inoculation with selected PGPR as a viable economical and environment‐friendly alternative to chemical fertilization in salinity‐affected soils.     

Effect of a legume cover crop (Mucuna pruriens var. utilis) on soil carbon in an Ultisol under maize cultivation in southern Benin

Abstract. Long term fallow is no longer possible in densely populated tropical areas, but legume cover crops can help maintain soil fertility. Our work aimed to study changes in soil carbon in a sandy loam Ultisol in Benin, which involved a 12-year experiment on three maize cropping systems under manual tillage: traditional no-input cultivation (T), mineral fertilized cultivation (NPK), and association with Mucuna pruriens (M). The origin of soil carbon was also determined through the natural abundance of soil and biomass ¹³C. In T, NPK and M changes in soil carbon at 0–40 cm were −0.2, +0.2 and +1.3 t C ha⁻¹ yr⁻¹, with residue carbon amounting to 3.5, 6.4 and 10.0 t C ha⁻¹ yr⁻¹, respectively. After 12 years of experimentation, carbon originating from maize in litter-plus-soil (0–40 cm) represented less than 4% of both total carbon and overall maize residue carbon. In contrast, carbon originating from mucuna in litter-plus-soil represented more than 50% of both total carbon and overall mucuna residue carbon in M, possibly due to accelerated mineralization of native soil carbon (priming effect) and slow mulch decomposition. Carbon originating from weeds in litter-plus-soil represented c. 10% of both total carbon and overall weed residue carbon in T and NPK. Thus mucuna mulch was very effective in promoting carbon sequestration in the soil studied.     

Long-term effects of various crop rotations for managing salt-affected soils through a field scale decision support system – a case study

Appropriate crop rotations coupled to water use plans are the basic means of managing salt‐affected soils. Recommendation of suitable crop rotations for salt‐affected land requires prediction of their long‐term impact on soil salinity/sodicity build‐up and consequent crop yield reduction. This is conventionally achieved through long‐term field experiments. However, such evaluations are site specific, expensive and time consuming. Appropriate decision support systems (DSS) can be a cost‐effective means in such cases. This study demonstrates the application of one such DSS for recommending the best crop rotation for a salt‐affected field in Gurgaon district of Haryana (India). Before application, the DSS was extensively validated on 11 farmer's fields and one experimental field in Gurgaon and Karnal districts of Haryana. The DSS gave realistic estimates of root zone soil salinity/sodicity and relative crop yield reductions under the local management practices. These estimates were associated with absolute mean relative errors ranging between 0.02 and 0.24. Ten‐year impact assessments of existing (i.e. paddy–wheat, P‐W) and 10 alternative crop rotation plans with the validated DSS showed that pearl millet‐based sequences were, environmentally and agronomically, the most suitable options for the test field. However, a cost–benefit analysis of DSS‐simulated average annual crop yields, under various crop rotations, showed that the economic return of pearl millet‐based sequences was about 13% less than fallow–wheat (F‐W) rotations and 4% less than P‐W rotations. Hence F‐W was recommended as the most beneficial environmental choice and economically the most robust alternative crop sequence for the salt‐affected field.     

Apoplast acidification is not a necessary determinant for the resistance of maize in the first phase of salt stress

In previous studies, a relation between plant growth during the first phase of salt stress and cell‐wall acidification was shown for differently resistant maize genotypes. In the present study, plants of the salt‐sensitive maize (Zea mays L.) cv. Pioneer 3906 and the salt‐resistant genotype SR 12, grown under 100 mM NaCl, showed a similar decrease in plasmalemma H⁺‐ATPase activity, while SR 12 showed less growth reduction than Pioneer 3906. From this it is concluded that maintenance of apoplast acidification is not necessary for better plant growth during the first phase of salt stress.     

Effects of NaCl salinity on some leaf nutrient concentrations,non-photochemical quenching and the efficiency of the PSII photochemistry of two Iranian pomegranate varieties under greenhouse and field conditions: Preliminary results

The present research was conducted to study the responses of ‘Malas–e–Saveh’ (M) and ‘Shishe–Kab’ (Sh) Iranian pomegranates to sodium chloride (NaCl) stress under greenhouse and field conditions. Treatments included waters electrical conductivity (EC = 1.5, 3, 6, 9 and 12 dS m^?1 for greenhouse) and (EC = 1.05 as control, 4.61 and 7.46 dS m^?1 for field studies). Interactive effects of salinity × variety indicated the highest chlorophyll and leaf potassium concentration, and the lowest leaf chloride and sodium in control under greenhouse study. Non-photochemical quenching, effective quantum yield of photochemical energy conversion in PSII reduced under the highest salinity level in field, however, basal quantum yield of non-photochemical processes in PSII increased in the highest salinity. Sodium and chloride increased with increased in salinity. Calcium, magnesium and iron significantly decreased with increased in salinity. It seems that there are differences between pomegranate cultivars and Malas-e-Saveh is more tolerant compared with Shishe Kab.     

Effects of pentachlorophenol in forest soil: a microcosm experiment for testing ecosystem responses to anthropogenic stress

Changes in the structure and function of a soil decomposer community and growth of birch (Betula pendula) due to chemical contamination were studied in laboratory microcosms. Sodium pentachlorophenate (PCP) was added to the humus layer of a simulated forest soil at three nominal concentrations (0, 50 and 500 mg kg^-1 dry mass). After two growing periods (48 weeks), there were more small soft-bodied mites, but less collembolans and microbial biomass, in the higher PCP concentration treatment than in the other treatments. Number of enchytraeids were significantly reduced and fungal-feeding nematodes became extinct in the soil with the higher PCP concentration. Soil respiration did not change due to PCP contamination. Diversity of soil fauna tended to decrease with increasing PCP concentration. Number of faunal taxa were not influenced by PCP. Mainly due to reduction of enchytraeids, total animal biomass was significantly lower in the higher PCP concentration treatment than in the other treatments. At week 8, leaching of nutrients was greatest in the higher PCP concentration treatment. At the end of the experiment no significant changes in soil pH and NH _inf4 ^sup+ -N content of the soil were found. Birch growth and N concentration of the leaves were reduced with the higher PCP concentration. We assume that direct toxicity of PCP at the beginning of the experiment and changes in the decomposer community structure (mainly reduction of enchytracids and changes in microflora) due to PCP were responsible for the lowered primary production in the systems.     

Biochar and crop residue application to soil: effect on soil biochemical properties,nutrient availability and yield of rice (Oryza sativa L.) and wheat (Triticum aestivum L.)

In the recent past, biochar and crop residues have attracted lots of attention as a viable strategy for maintaining soil health. This paper evaluates the comparative effect of two different doses (equivalent to 2 and 5 t C ha^?1) of each of pine needle and Lantana biochar (PBC and LBC), wheat residue and lentil residue (WR and LR) on soil biological properties, nutrient availability and yield of rice and wheat in pot culture. Energy-dispersive X-ray spectroscopy (EDS) revealed higher C content of biochar than crop residues. Evaluation of biochemical quality reflected high recalcitrance indices of C and N for both PBC and LBC. Application of LBC and PBC increased the wheat grain yield significantly by 6.2%–24.2% over control. Both PBC and LBC significantly increased N and P uptakes in grain over the control and crop residues. Both biochars recorded a significant decrease of 33.9 and 71,7% in β-glucosidase activity in comparison to control at termination of study. PBC and LBC also resulted in more soil available N, P and K in soil at different intervals. The geometric mean of enzyme activities (GMea) reflected improved soil quality by PBC and LR and reduction by LBC application.