Arbuscular mycorrhizal fungus and rhizobacteria affect the physiology and performance of Sulla coronaria plants subjected to salt stress by mitigation of ionic imbalance

Salt stress has become a major menace to plant growth and productivity. The main goal of this study was to investigate the effect of inoculation with the arbuscular mycorrhizal fungi (AMF; Rhizophagus intraradices) in combination or not with plant growth‐promoting rhizobacteria (PGPR; Pseudomonas sp. (Ps) and Bacillus subtilis) on the establishment and growth of Sulla coronaria plants under saline conditions. Pot experiments were conducted in a greenhouse and S. coronaria seedlings were stressed with NaCl (100 mM) for 4 weeks. Plant biomass, mineral nutrition of shoots and activities of rhizosphere soil enzymes were assessed. Salt stress significantly reduced plant growth while increasing sodium accumulation and electrolyte leakage from leaves. However, inoculation with AMF, whether alone or combined with the PGPR Pseudomonas sp. alleviated the salt‐induced reduction of dry weight. Inoculation with only AMF increased shoot nutrient concentrations resulting in higher K⁺: Na⁺, Ca²⁺: Na⁺, and Ca²⁺: Mg²⁺ ratios compared to the non‐inoculated plants under saline conditions. The co‐inoculation with AMF and Pseudomonas sp. under saline conditions lowered shoot sodium accumulation, electrolyte leakage and malondialdehyde (MDA) levels compared to non‐inoculated plants and plants inoculated only with AMF. The findings strongly suggest that inoculation with AMF alone or co‐inoculation with AMF and Pseudomonas sp. can alleviate salt stress of plants likely through mitigation of NaCl‐induced ionic imbalance, thereby improving the nutrient profile.     

Halophile plant growth-promoting rhizobacteria induce salt tolerance traits in wheat seedlings (Triticum aestivum L.)

Salinity is one of the most important growth-limiting factors for most crops in arid and semi-arid regions; however, the use of plant growth-promoting rhizobacteria isolated from saline soils could reduce the effects of saline stress in crops. This study aimed to evaluate the efficiency of plant growth-promoting rhizobacteria (PGPRs), isolated from the rhizosphere of halophile plants, for the growth, Na⁺/K⁺ balance, ethylene emission, and gene expression of wheat seedlings (Triticum aestivum L.) grown under saline conditions (100 mmol L^-1 NaCl) for 14 d. A total of 118 isolates obtained from saline soils of the deserts of Iran were tested for their capacity as PGPRs. Out of the 118 isolates, 17 could solubilize phosphate (Ca₃(PO₄)₂), 5 could produce siderophores, and 16 could synthesize indole-3-acetic acid. Additionally, PGPRs were also evaluated for aminocyclopropane-1-carboxylate deaminase activity. A pot experiment was conducted to evaluate the ability of 28 PGPR isolates to promote growth, regulate Na⁺/K⁺ balance, and decrease ethylene emissions in plants. The most efficient PGPRs were Arthrobacter aurescens, Bacillus atrophaeus, Enterobacter asburiae, and Pseudomonas fluorescens. Gene expression analysis revealed the up-regulation of H⁺-PPase, HKT1, NHX7, CAT, and APX expression in roots of Enterobacter-inoculated salt-stressed plants. Salt-tolerant rhizobacteria exhibiting plant growth-promoting traits can facilitate the growth of wheat plants under saline conditions. Our results indicate that the isolation of these bacteria may be useful for formulating new inoculants to improve wheat cropping systems in saline soils.     

在受控条件下植物促生菌对扁豆的生长，结瘤和养分积累的效应

Application of plant growth-promoting rhizobacteria (PGPR) has been shown to increase legume growth and development under field and controlled environmental conditions. The present study was conducted to isolate plant growth-promoting rhizobacteria (PGPR) from the root nodules of lentil (Lens culinaris Medik.) grown in arid/semi-arid region of Punjab, Pakistan and examined their plant growth-promoting abilities. Five bacterial isolates were isolated, screened in vitro for plant growth-promoting (PGP) characteristics and their effects on the growth of lentil were assessed under in vitro, hydroponic and greenhouse (pot experiment) conditions. All the isolates were Gram negative, rod-shaped and circular in form and exhibited the plant growth-promoting attributes of phosphate solubilization and auxin (indole acetic acid, IAA) production. The IAA production capacity ranged in 0.5-11.0 μg mL-1 and P solubilization ranged in 3-16 mg L-1 . When tested for their effects on plant growth, the isolated strains had a stimulatory effect on growth, nodulation and nitrogen (N) and phosphorus (P) uptake in plants on nutrient-deficient soil. In the greenhouse pot experiment, application of PGPR significantly increased shoot length, fresh weight and dry weight by 65%, 43% and 63% and the increases in root length, fresh weight and dry weight were 74%, 54% and 92%, respectively, as compared with the uninoculated control. The relative increases in growth characteristics under in vitro and hydroponic conditions were even higher. PGPR also increased the number of pods per plant, 1 000-grain weight, dry matter yield and grain yield by 50%, 13%, 28% and 29%, respectively, over the control. The number of nodules and nodule dry mass increased by 170% and 136%, respectively. After inoculation with effective bacterial strains, the shoot, root and seed N and P contents increased, thereby increasing both N and P uptake in plants. The root elongation showed a positive correlation (R2 = 0.67) with the IAA production and seed yield exhibited a positive correlation (R2 = 0.82) with root nodulation. These indicated that the isolated PGPR rhizobial strains can be best utilized as potential agents or biofertilizers for stimulating the growth and nutrient accumulation of lentil.     

EFFECT OF PLANT GROWTH-PROMOTING RHIZOBACTERIA STRAIN ON FREEZING INJURY AND ANTIOXIDANT ENZYME ACTIVITY OF WHEAT AND BARLEY

In 2009 a greenhouse experiment was conducted to determine the effects of boron (B) and plant growth-promoting rhizobacteria (PGPR) on wheat (Triticum aestivum spp. vulgare cv ‘Bezostiya’) and barley (Hordeum vulgare cv ‘Tokak’) on plant growth, freezing injury, and antioxidant enzyme capacity. Results showed that boron (0, 1, 3, 6, 9 kg B ha^?1) and PGPR application (Bacillus megaterium M3, Bacillus subtilis OSU142, Azospirillum brasilense Sp245 and Raoultella terrigena) at which 50% of leaves were injured (LT₅₀) values and ice nucleation activities in both plants were found statistically significant. Boron application with all PGPR strains decreased LT₅₀ values in wheat and barley plants under noncold stress (NCS) and cold stress conditions (CS). There were statistically significant differences between bacterial inoculation and B fertilizer in terms of root and shoot dry weight under NCS and CS conditions. Reactive oxidative oxygen species (ROS) and antioxidant enzyme activities (SOD, POD, CAT) were negatively affected CS conditions and decreased with reduced temperatures of media, but B and PGPR applications alleviated the low-temperature deleterious effects in both plants species tested. The lowest ROS and antioxidant enzyme (SOD, POD, CAT) of wheat and barley were observed with 6 kg B ha^?1 with R. terrigena.     

Alleviation of Salt Stress in Eggplant (Solanum melongena L.) by Plant-Growth-Promoting Rhizobacteria

This study was conducted to elucidate the effects of inoculation with plant-growth-promoting rhizobacteria (PGPR) on eggplant growth, yield, and mineral content under salt stress [0, 25, and 50 mM sodium chloride (NaCl)]. The PGPR strains Xanthobacter autotrophicus BM13, Enterobacter aerogenes BM10, and Bacillus brevis FK2 were isolated from the salt-affected maize and kidney bean fields. The increase in salinity decreased the growth and yield and increased the sodium (Na⁺) uptake of eggplant. However, inoculation with PGPR strains reduced the negative effects at each level of salinity tested. The E. aerogenes strain was capable of promoting eggplant growth and yield when compared to an uninoculated control. The B. brevis was the most effective strain for reducing the negative effects of salinity, and its effects occurred through increasing the potassium (K⁺)/Na⁺ ratio and K⁺-Na⁺ selectivity in the eggplant shoots. Inoculation of the eggplant seedlings with PGPR could alleviate the negative effects of salt stress.     

Use of Potassium Fertilization to Ameliorate the Adverse Effects of Saline-sodic Stress Condition (ECw: SARw Levels) in Rice (Oryza Sativa L.)

ABSTRACT

Salt-affected soils expand around the world and become a critical handicap for high crop yield. Saline-sodic soil contributed a major portion in salt-affected soils. Such types of soils have a sizable amount of Na⁺ in nutrient medium and that reduce the K⁺ uptake in plants. A hydroponic experiment was performed to investigate the ameliorative effect of different doses of potassium fertilizer (K₁ = 0.3, K₂ = 0.6 and K₃ = 1.2 mM L^?1) on rice (Oryza sativa L.) under different EC_w (6 dS m^?1) and SAR_w [12 and 24 (mmol L^?1)^1/2] levels. Application of K⁺ at elevated levels under saline-sodic conditions improved the concentration of anti-oxidant enzymes, plant physiological, and biochemical attributes by improving the K⁺: Na⁺ ratio in plant tissues. Total phenolic content, total soluble protein, and soluble sugar content of rice plant were increased with an increase in potassium dose and saline-sodicity. Maximum K⁺: Na⁺ ratios, 4.13 and 2.0 were observed in shoot and root, respectively upon application of K⁺ at 1.2 mM L^?1 in a solution having EC_w: SAR_w level of 6: 12. This study suggested that application of potassium at elevated levels (1.2 mM L^?1) has enhanced the rice growth by reducing the harmful effect of Na⁺ salts on plant physiology, biochemical attributes, and anti-oxidant enzymes under specific saline-sodic conditions.     

Effects of plant growth-promoting bacteria on the phytoremediation of cadmium-contaminated soil by sunflower

This paper describes the effect of plant growth-promoting bacteria on sunflower growth and its phytoremediation efficiency under Cd-contaminated soils. Four levels of bacteria inoculation (non-inoculation, inoculation by Bacillus safensis, Kocuria rosea and co-inoculation by Bacillus safensis+Kocuria rosea) and four Cd concentrations (0, 50, 100 and 150 mg Cd per kg soil) were arranged as factorial experiment based on a completely randomized design (CRD). Results showed that Cd significantly decreased growth by decreasing the shoot and root length and biomass (p < 0.01). In addition, Cd dramatically decreases photosynthetic pigments, Fe transport to shoot and Zn uptake (p < 0.01). Bacterial inoculation increased Fe and Zn uptake by plants, Cd concentration in the aboveground part of plants and Cd uptake by the enhancement of Cd concentration in plant tissue and biomass production. Results showed that the highest shoot Cd uptake was ?observed in ?inoculated plants by Bacillus safensis at Cd100 (20.35 mg pot^?1). However, in average of Cd treatments, the performance of co-inoculation in Cd uptake (13.04 mg pot^?1) was better than singular inoculation (10.68 and 12.58 mg pot^?1 for Bacillus safensis and Kocuria rosea, respectively). Results revealed that bacterial inoculation increased the Cd uptake performance in shoot and total biomass by 30% and 25%, respectively.     

Role of carrier-based biofertilizer in reclamation of saline soil and wheat growth

Two plant growth promoting rhizobacteria (PGPR), Pseudomonas moraviensis and Bacillus cereus, were used as bioinoculants on wheat, applied alone and in combination. Ground maize straw and sugarcane husk were used as carriers. Experiment was conducted for two consecutive years (2010 and 2011) under axenic conditions in the greenhouse of Quaid-e-Azam University, Islamabad. Sodium chloride (NaCl) (150 mM) was applied with irrigated water after 7 and 14 days of seed germination. Measurements made 40 days after sowing (DAS) revealed that P. moraviensis and B. cereus have better survival efficiency (as evidenced by higher colony forming units (CFUs)) in the carriers. The substantial increase in CFU of both PGPR was also observed in the soil at 57 DAS. Coinoculation of PGPR with both the carrier materials significantly decreased electrical conductivity (EC) and Na⁺ content of soil over control. The N, P, K⁺, Ca⁺, and Mg⁺ contents were 30–40% higher in soil, and 30–45% higher in leaves. Coinoculation of PGPR with carriers significantly increased chlorophyll, protein, sugar, phytohormone contents, and antioxidant activities of leaves. The application of biofertilizers improved the yield of wheat by 15–25% over control. It is inferred that the carriers assisted PGPR for long-time survival, and the formulation was applicable in promoting crop production under salt stress.     

Screening of rhizobacteria isolated from maize (Zea mays L.) in Rio Grande do Sul State (South Brazil) and analysis of their potential to improve plant growth

Plant growth-promoting rhizobacteria (PGPR) are considered to have a beneficial effect on host plants and may facilitate plant growth by different mechanisms. In this work, the influence of different soil types on the bacterial diversity and the stimulatory effects of selected PGPR on two cultivars of maize were investigated. A set of 292 strains was isolated from the roots and rhizosphere soil of maize cultivated in five different areas of the Rio Grande do Sul State in Brazil. 16S rDNA-PCR-RFLP and 16S rDNA partial sequencing were used for identification, and the Shannon–Weaver index was used to evaluate bacterial diversity. We evaluated the ability of each isolate to produce indole acetic acid (IAA), siderophores and solubilize phosphates. On the basis of multiple PGP traits, six isolates were selected to test their potential as plant growth-promoting rhizobacteria on maize plants. In both the roots and the rhizospheric soil of maize, the dominant bacterial genera identified were Klebsiella and Burkholderia. IAA producers were distributed widely among isolates, regardless of the sampling site. Approximately 42% of the isolates exhibited at least two attributes, and 24% showed all three PGP traits. Three strains, identified as Achromobacter, Burkholderia, and Arthrobacter, were effective as PGPR in both of the cultivars evaluated.     

Plant Growth-Promoting Rhizobacteria (PGPR) and Phosphorus Fertilizer-Assisted Phytoextraction of Toxic Heavy Metals from Contaminated Soils

Phytoremediation is a remediation technique that involves the use of plants to extract, sequester, and/or detoxify pollutants through physical, chemical, and biological processes. The use of phytoremediation is expanding due to its cost-effectiveness compared with conventional methods. This study was conducted to investigate the effects of autumn and spring application of plant growth-promoting rhizobacteria (PGPR, 10⁸ cfu mL^?1 Bacillus megaterium var. phosphaticum sprayed at 250 mL plot^?1) and phosphorus (P) fertilizer (0, 11, 22, 33, 44 kg P ha^?1) on dry matter yield and heavy metal uptake by plants in soils contaminated with heavy metals. Field experiments were conducted using a randomized complete block design with four replications between 2004 and 2007. The results of the study indicated that P fertilization, but not PGPR application, significantly affected dry matter yield. Application of PGPR increased heavy metal availability in soils and the heavy metal uptake of meadow plants. The heavy metal content of the meadow plants resulting from PGPR application was 4–6 times higher for the spring application than the autumn application. Approximately 16, 30, 10, 10, and 3 growing seasons without PGPR are necessary to remove all lead (Pb), nickel (Ni), boron (B), manganese (Mn), and zinc (Zn), respectively, from polluted soil. The time required for Pb, Ni, B, Mn, and Zn removal could be further decreased to approximately 4, 6, 3, 3, and 1 growing seasons, respectively, with 33 kg phosphorus pentoxide (P₂O₅) ha^?1 and 10⁸ cfu mL^?1 PGPR applications at rates of 250 mL plot^?1 in the spring season.     

AMF和PGPR修复甲胺磷污染土壤的效应

丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)和根围促生细菌(plant growthpromoting rhizobacteria,PGPR)能降解有毒有机物,但分解土壤中残留甲胺磷农药尚未见报道。本试验旨在测定AMF和PGPR矿化甲胺磷的效应。试验设甲胺磷0、50、100和150μg g-1下,对番茄(Lycospersicon esculentum,品种金冠)接种AMF Glomus mosseae(Gm)、Glomus etunicatum(Ge)、PGPR Bacillus subtilis(Bs)、Bacillus sp.B697(Bsp)、Pseudomonas fluorescens(Pf)、Gm+Bs、Gm+Bsp、Gm+Pf、Ge+Bs、Ge+Bsp、Ge+Pf和不接种对照,共48个处理。结果表明,接种Gm显著增加了根区土壤和根内PGPR定殖数量,而Pf处理显著提高了AMF侵染率,表明Gm与Pf能够相互促进。甲胺磷100μg g-1水平下,Gm+Pf处理的番茄株高显著高于其他处理,地上部干重显著高于其他处理(Ge+Pf除外),根系干重显著高于对照、PGPR各处理和Ge处理;而根内甲胺磷浓度则显著低于其他处理,茎叶中的则显著低于其他处理(Gm+Bs、Gm+Bsp和Ge+Pf除外)。AMF、PGPR或AMF+PGPR处理均显著降低番茄体内甲胺磷浓度。甲胺磷50~100μg g-1水平下,Gm+Pf显著降低根区土壤中甲胺磷残留量,矿化率达52%~60.6%。AMF和PGPR显著提高了根区土壤中甲胺脱氢酶活性,其中以Gm+Pf组合处理的酶活性最高。表明AMF和PGPR均能促进土壤中残留甲胺磷的降解,Gm+Pf是本试验条件下的最佳组合。     

Effects of Plant Growth-Promoting Rhizobacteria and N Source on Plant Growth and N and P Uptake by Tomato Grown on Calcareous Soils

Introducing specific microorganisms into the soil ecological system is an important strategy for improving nutrient use efficiency. Two pot experiments were conducted in the greenhouse from December 3, 2012 to January 25, 2013 (Experiment 1) and March 11 to April 23, 2013 (Experiment 2) to evaluate the effect of nitrogen (N) source and inoculation with plant growth-promoting rhizobacteria (PGPR) on plant growth and N and phosphorus (P) uptake in tomato (Lycopersicon esculentum Mill.) grown on calcareous soils from South Florida, USA. Treatments included urea, controlled release urea (a controlled release fertilizer, CRF) each at low and high N rates and with or without inoculation of PGPR. A mixture of PGPR strains Bacillus amyloliquefaciens IN937a and Bacillus pumilus T4 was applied to the soil during growing periods of tomato. Treatments with PGPR inoculation increased plant height compared to treatments without PGPR in both experiments. Inoculation with PGPR increased shoot dry weight and shoot N uptake for the same N rate and N source. In both experiments, only at high N rate, CRF and urea treatments with PGPR had significantly (P < 0.05) greater shoot biomass than those without PGPR. Only at high N rate, CRF treatment with PGPR significantly increased shoot N uptake by 39.0% and 10.3% compared to that without PGPR in Experiments 1 and 2, respectively. Meanwhile, presence of PGPR in the soil increased shoot P uptake for all treatments in Experiment 1 and for most treatments in Experiment 2. In Experiment 1, only at low N rate, CRF treatment with PGPR significantly increased shoot P uptake compared with that without PGPR. In Experiment 2, a significant increase in shoot P uptake by inoculation of PGPR was only observed in CRF treatment at high N rate. Results from this study indicate that inoculation with PGPR may increase plant growth and N and P uptake by tomato grown on calcareous soils. However, the effect of PGPR varied and was influenced by many factors such as N source, N rate, and soil fertility. Further investigations are warranted to confirm the effect of PGPR under different soil conditions.     

Consequences of sodium exclusion for the osmotic potential in the rhizosphere – Comparison of two maize cultivars differing in Na+ uptake

According to the biphasic model of growth response to salinity, growth is first reduced by a decrease in the soil osmotic potential (Ψ_o), i.e., growth reduction is an effect of salt outside rather than inside the plant, and genotypes differing in salt resistance respond identically in this first phase. However, if genotypes differ in Na⁺ uptake as it has been described for the two maize cultivars Pioneer 3906 and Across 8023, this should result in differences in Na⁺ concentrations in the rhizosphere soil solution and thus in the concentration of salt outside the plant. It was the aim of the present investigation to test this hypothesis and to investigate the effect of such potential differences in soil Ψ_o caused by Na⁺ exclusion on plant water relations. Sodium exclusion at the root surface of intact plants growing in soil was investigated by sampling soil solution from the rhizosphere of two maize cultivars (Across 8023, Pioneer 3906). Plants were grown in a model system, consisting of a root compartment separated from the bulk soil compartment by a nylon net (30 μm mesh size), which enabled independent measurements of the change of soil solution composition and soil water content with increasing distance from the root surface (nylon net). Across 8023 accumulated higher amounts of sodium in the shoot compared to the excluder (Pioneer 3906). The lower Na⁺ uptake in the excluder was partly compensated by higher K⁺ uptake. Pioneer 3906 not only excluded sodium from the shoot but also restricted sodium uptake more efficiently from roots relative to Across 8023. This was reflected by higher Na⁺ concentrations in the rhizosphere soil solution of the excluder 34 days after planting (DAP). The difference in Na⁺ concentration in rhizosphere soil solution between cultivars was neither due to differences in transpiration and thus in mass flow, nor due to differences in actual soil water content. As the lower Na⁺ uptake of the excluder (Pioneer 3906) was only partly compensated by increased uptake of K⁺, soil Ψ_o in the rhizosphere of the excluder was more negative compared to Across 8023. However, no significant negative effect of decreased soil Ψ_o on plant water relations (transpiration rate, leaf Ψ_o, leaf water potential, leaf area) could be detected. This may be explained by the fact that significant differences in soil Ψ_o between the two cultivars occurred only towards the end of the experiment (27 DAP, 34 DAP).     

Effect of nitrogen source and salinity level on salt accumulation of two chickpea genotypes

This study aimed at investigating mechanisms of salt tolerance and ionic relations of chickpea (Cicer arietinum L.) cultivars with different nitrogen (N) sources. Two resistant genotypes, ILC‐205 and ILC‐1919, were subjected to four levels of salinity (0.5, 3.0, 6.0, and 9.0 dS m^‐1). Nitrogen sources consisted of inoculation with two resistant Rhizobium strains, CP‐29 and CP‐32, mineral N additions, and no N application. Data was collected on root and shoot contents of sodium (Na⁺) chlorine, (Cl^‐,) and potassium (K⁺), and shoot to root Na⁺ratio, as well as shoot K⁺ to Na⁺ ratio. Salinity affected shoot Na⁺ and Cl^‐contents, but nodulating plants had higher shoot Na⁺ contents than plants supplied with mineral N. Shoot to root Na⁺ ratios were lower in the mineral N treatment than in nodulating treatments at 3.0 dS m^‐1, indicating that root compartmentalization and shoot exclusion were only possible at low salinities. Potassium levels of nodulating plant shoots were lower than those of non‐nodulating plants only at low salinities. N‐source significantly affected shoot K⁺/Na⁺ ratio, with nodulating plants having lower ratios than non‐nodulating plants, indicating that rhizobial infection or nodule formation may lead to salt entry curtailing the selective ability of chickpea roots.     

抗重金属植物根际细菌的植物促生长特征以及它们对黑芥种子萌发的影响

Phytoremediation is an emerging technology that uses plants and their associated microbes to clean up pollutants from the soil, water, and air. In order to select the plant growth-promoting rhizobacteria(PGPR) for phytoremediation of heavy metal contamination, 60 bacterial strains were isolated from the rhizosphere of two endemic plants, Prosopis laevigata and Spharealcea angustifolia, in a heavy metal-contaminated zone in Mexico. These rhizobacterial strains were characterized for the growth at different pH and salinity, extracellular enzyme production, solubilization of phosphate, heavy metal resistance, and plant growth-promoting(PGP) traits, including production of siderophores and indol-3-acetic acid(IAA). Overall, the obtained rhizobacteria presented multiple PGP traits. These rhizobacteria were also resistant to high levels of heavy metals(including As as a metalloid)(up to 480 mmol L(-1)As(V), 24 mmol L(-1)Pb(Ⅱ), 21 mmol L(-1)Cu(Ⅱ), and 4.5 mmol L(-1)Zn(Ⅱ)). Seven rhizobacterial strains with the best PGP traits were identified as members of Alcaligenes, Bacillus, Curtobacterium, and Microbacterium, and were selected for further bioassay.The inoculation of Brassica nigra seeds with Microbacterium sp. CE3R2, Microbacterium sp. NE1R5, Curtobacterium sp. NM1R1,and Microbacterium sp. NM3E9 facilitated the root development; they significantly improved the B. nigra seed germination and root growth in the presence of heavy metals such as 2.2 mmol L(-1)Zn(Ⅱ). The rhizobacterial strains isolated in the present study had the potential to be used as efficient bioinoculants in phytorremediation of soils contaminated with multiple heavy metals.     

An AM fungus and a PGPR intensify the adverse effects of salinity on the stability of rhizosphere soil aggregates of Lactuca sativa

A mesocosm experiment was conducted to examine the effect of an arbuscular mycorrhizal (AM) fungus (Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe) and a plant growth-promoting rhizobacterium (PGPR) (Pseudomonas mendocina Palleroni), alone or in combination, on the structural stability of the rhizosphere soil of Lactuca sativa L. grown under two levels of salinity. The plants inoculated with P. mendocina had significantly greater shoot biomass than the control plants at both salinity levels, whereas the mycorrhizal inoculation was only effective in increasing shoot biomass at the moderate salinity level. The aggregate stability of soils inoculated with the PGPR and/or G. mosseae significantly decreased with increasing saline stress (about 29% lower than those of soils under non-saline conditions). Only the inoculated soils showed higher concentrations of sodium (Na) under severe saline stress. The severe salinity stress decreased the glomalin-related soil protein (GRSP) concentration, but the highest values of GRSP were recorded in the inoculated soils. Our findings suggest that the use of AM fungi and/or a PGPR for alleviating salinity stress in lettuce plants could be limited by their detrimental effect on soil structural stability.     

滨海盐渍土的碱化问题

滨海盐渍土是否有碱化问题,特别是在开垦利用以后,土壤是否会向碱化方向演化,这是很多生产单位所关心的问题。对此,过去已做了不少工作。有人认为滨海盐渍土由于长期受海水浸渍,土壤胶体表面吸附着大量的钠离子,因此有比较高的碱化度,盐渍程度愈重则碱化度愈高,随着土壤脱盐同时脱碱,当不致进一步碱化^[3]。也有人认为滨海盐债土耕垦后不会发生碱化,其碱化度随改良利用年限而降低^[1]。还有人在滨海盐溃土耕垦种稻后,观测到在土壤脱盐过程中,土壤pH值和总碱度有所增高,认为土壤发生了碱化^[2,5]1)。我们就这一间题曾先后对浙江上虞、乐清,江苏东台、大丰、滨海、灌云以及辽宁兴城、锦县、大洼等县的滨海地区进行了调查研究和室内试验。     

Effects of mineral and biofertilizers on barley growth on compacted soil

Abstract

Biofertilizers are an alternative to mineral fertilizers for increasing soil productivity and plant growth in sustainable agriculture. The objective of this study was to evaluate possible effects of three mineral fertilizers and four plant growth promoting rhizobacteria (PGPR) strains as biofertilizer on soil properties and seedling growth of barley (Hordeum vulgare) at three different soil bulk densities, and in three harvest periods. The application treatments included the control (without bacteria inoculation and mineral fertilizers), mineral fertilizers (N, NP and P) and plant growth promoting rhizobacteria species (Bacillus licheniformis RC04, Paenibacillus polymyxa RC05, Pseudomonas putida RC06, and Bacillus OSU-142) in sterilized soil. The PGPR, fungi, seedling growth, soil pH, organic matter content, available P and mineral nitrogen were determined in soil compacted artificially to three bulk density levels (1.1, 1.25 and 1.40 Mg m^?3) at 15, 30, and 45 days of plant harvest. The results showed that all the inoculated bacteria contributed to the amount of mineral nitrogen. Seed inoculation significantly increased the count of bacteria and fungi. Data suggest that seed inoculation of barley with PGPR strains tested increased root weight by 9–12.2%, and shoot weight by 29.7–43.3% compared with control. The N, NP and P application, however, increased root weight up to 18.2, 25.0 and 7.4% and shoot weight by 31.6, 43.4 and 26.4%, respectively. Our data show that PGPR stimulate barley growth and could be used as an alternative to chemical fertilizer. Soil compaction hampers the beneficial plant growth promoting properties of PGPR and should be avoided.     

修复剂对镉污染盐渍化土壤植物修复效率的影响

目前,重金属污染盐渍化土壤已成为世界性的环境问题,利用盐生植物进行修复具有良好的环境与经济效益,但如何提高盐生植物修复效率的研究尚较少。采用盆栽试验方法,通过向土壤中施加氯化钠和氯化镉溶液分别模拟无污染非盐渍化土壤(Cd0S0)、NaCl型盐渍化土壤(Cd0S4)、重金属Cd污染土壤(Cd3S0)、重金属Cd污染NaCl型盐渍化土壤(Cd3S4),研究施加乙二胺四乙酸(EDTA)和生物质炭对盐地碱蓬生长、离子平衡、Cd和Na⁺吸收的影响。结果显示,与Cd0S0相比,Cd0S4处理盐地碱蓬地上部干物质量显著增加115.5%~341.7%;与Cd0S4相比,Cd3S4处理盐地碱蓬地上部干物质量显著降低62.8%~84.4%,生物质炭使Cd3S0处理盐地碱蓬总干物质量显著增加328.6%。与Cd0S0或Cd3S0相比,Cd0S4和Cd3S4处理盐地碱蓬地上部及根部K⁺/Na⁺、Ca²⁺/Na⁺、P/Na⁺显著降低;生物质炭显著增加了Cd3S0处理盐地碱蓬地上部P/Na⁺和根部K⁺/Na⁺、P/Na⁺。与Cd0S4相比,Cd3S4处理盐地碱蓬地上部和根部Na⁺浓度显著增加32.5%~94.5%,而盐地碱蓬地上部和根部Na⁺含量显著降低21.3%~90.9%;与Cd3S0相比,Cd3S4处理盐地碱蓬地上部Cd浓度和含量分别显著增加135.8%~223.6%和132.4%~471.5%。施加EDTA和生物质炭使Cd3S4处理盐地碱蓬地上部Na⁺浓度显著增加38.6%、56.0%,Na⁺含量增加199.6%、289.3%,Cd含量显著增加133.4%、173.4%。研究表明,在Cd污染NaCl型盐渍化土壤中施用EDTA和生物质炭可促进盐地碱蓬地上部对Cd和Na⁺的吸收积累,有助于提高植物修复效率,可为重金属污染盐渍化土壤修复提供基础数据和科学依据。     

胀果甘草原生境土壤盐分特征分析

 通过野外调查采样和土样化学测定,分析胀果甘草原生境下土壤盐分的特征。结果表明:研究区土壤盐分普遍较高且表聚作用明显,土壤表层0～10 cm土层盐分均值高达32+.08g/kg,属典型的强度盐渍化土;土壤盐分组成中,含阳离子Ca2+、Na+、Mg2+、K+和阴离子Cl-、SO24、HCO-3,不含CO2-3,土壤盐分的特征因子为Ca2+、C1-、SO2-4、NaCa+,其盐渍类型主要为硫酸盐-氯化物型,重碳酸盐是土壤盐分的次要成分;该生境土壤中在整个垂直剖面上Ca2+的含量丰富,属典型钙质土。