中国干旱区盐碱化土壤面积大，分布广，盐碱化作为土壤退化的一个重要方面，已严重影响了农业经济的可持续发展。中国作为土壤盐碱化危害最严重的国家之一，盐分的聚积及影响一直是干旱区研究的热点问题，全面开展土壤盐碱化的防治任重而道远。本文在分析干旱区土壤盐碱化的监测技术与方法的基础上，从土地利用、灌溉方式、自然环境因子等3个方面，综述了土壤盐分积累与运移过程及其影响因素，并认为：在盐碱化土地改良方面，应综合考虑各灌区的不同因素，探求既环保又经济的最佳组合改良模式；而在耐盐植物的筛选方面，应加强培育高效的土壤盐分改良植物。针对土壤盐分运移过程，提出了在流域或景观尺度上研究绿洲盐分运移过程的展望，以期为干旱区土壤盐碱化的防治和管理提供参考。

High soil salinity is the main factor that limits soil microbial activity in the Yellow River Delta (YRD); however, its effects on fungal community and ecological function are unknown. Here, we comparatively investigated the diversity and structures of soil fungal communities targeting the internally transcribed fungal spacer gene using Illumina MiSeq sequencing methods under a salt gradient with five levels, namely, Low: low-salinity soil, Medium: medium-salinity soil, High: high-salinity soil, Extreme: extreme-salinity soil, and a non-salted site as the control (Non-saline). The results show that bulk density (BD) values significantly increased (p < 0.05), while significantly lower values of soil total carbon (TC), total nitrogen (TN), and fungal Shannon and Chao indexes were observed as the salinization gradient increased (p < 0.05). The relatively high levels of the families Nectriaceae and Cladosporiaceae distinguished two of the clusters, indicating two enterotypes of low (Non-saline and Low) and high (Medium, High, and Extreme) salinity soils, respectively. The family Nectriaceae was most abundant in the networks, and the positive correlations were more pronounced than negative correlations; however, Cladosporiaceae was the family most negatively correlated with others based on the network analysis. At the ecological function level, plant saprotrophs and litter saprotroph were significantly less abundant in extremely saline soil than non-saline soil. The change in soil properties (TC, TN, and BD) caused by soil salinization [salt and electrical conductivity (EC)] regulated the diversity of soil fungal communities, and ecological function, as indicated by Pearson correlation analyses. We suggest further investigation into the ecological functions of soil microorganisms in the extremely saline-alkaline soils of the YRD.

Soil salinity is one of the major abiotic constraints in agricultural ecosystems worldwide. High salinity levels have negative impacts on plant growth and yield, and affect soil physicochemical properties. Salinity also has adverse effects on the distribution and abundance of soil microorganisms. Salinity problems have previously been addressed in research, but most approaches, such as breeding for salt tolerant varieties and soil amelioration, are expensive and require years of efforts. Halotolerant plant growth-promoting rhizobacteria (HT-PGPR) secrete secondary metabolites, including osmoprotectants, exopolysaccharides, and volatile organic compounds. The importance of these compounds in promoting plant growth and reducing adverse effects under salinity stress has now been widely recognised. HT-PGPR are emerging as effective biological strategies for mitigating the harmful effects of high salinity; improving plant growth, development, and yield; and remediating degraded saline soils. This review describes the beneficial effects and growth-promoting mechanisms of various HT-PGPR, which are carried out by maintaining ion homeostasis, increasing nutrient availability, and the producing secondary metabolites, osmoprotectants, growth hormones, and volatile organic compounds. Exploring suitable HT-PGPR and applications in agriculture production systems can play a crucial role in reducing the adverse impacts of salinity stress and sustainable crop productivity.

Salinity is one of the main causes of abiotic stress in plants, resulting in negative effects on crop growth and yield, especially in arid and semi-arid regions. The effects of salinity on plant growth mainly generate osmotic stress, ion toxicity, nutrient deficiency, and oxidative stress. Traditional approaches for the development of salt-tolerant crops are expensive and time-consuming, as well as not always being easy to implement. Thus, the use of plant growth-promoting bacteria (PGPB) has been reported as a sustainable and cost-effective alternative to enhance plant tolerance to salt stress. In this sense, this review aims to understand the mechanisms by which PGPB help plants to alleviate saline stress, including: (i) changes in the plant hormonal balance; (ii) release of extracellular compounds acting as chemical signals for the plant or enhancing soil conditions for plant development; (iii) regulation of the internal ionic content of the plant; or iv) aiding in the synthesis of osmoprotectant compounds (which reduce osmotic stress). The potential provided by PGPB is therefore an invaluable resource for improving plant tolerance to salinity, thereby facilitating an increase in global food production and unravelling prospects for sustainable agricultural productivity.

Salt stress is a major environmental stress that affects plant growth and development. Plants are sessile and thus have to develop suitable mechanisms to adapt to high-salt environments. Salt stress increases the intracellular osmotic pressure and can cause the accumulation of sodium to toxic levels. Thus, in response to salt stress signals, plants adapt via various mechanisms, including regulating ion homeostasis, activating the osmotic stress pathway, mediating plant hormone signaling, and regulating cytoskeleton dynamics and the cell wall composition. Unraveling the mechanisms underlying these physiological and biochemical responses to salt stress could provide valuable strategies to improve agricultural crop yields. In this review, we summarize recent developments in our understanding of the regulation of plant salt stress.

The plant faces different pedological and climatic challenges that influence its growth and enhancement. While, plant-microbes interactions throught the rhizosphere offer several privileges to this hotspot in the service of plant, by attracting multi-beneficial mutualistic and symbiotic microorganisms as plant growth-promoting bacteria (PGPB), archaea, mycorrhizal fungi, endophytic fungi, and others…). Currently, numerous investigations showed the beneficial effects of these microbes on growth and plant health. Indeed, rhizospheric microorganisms offer to host plants the essential assimilable nutrients, stimulate the growth and development of host plants, and induce antibiotics production. They also attributed to host plants numerous phenotypes involved in the increase the resistance to abiotic and biotic stresses. The investigations and the studies on the rhizosphere can offer a way to find a biological and sustainable solution to confront these environmental problems. Therefore, the interactions between microbes and plants may lead to interesting biotechnological applications on plant improvement and the adaptation in different climates to obtain a biological sustainable agricultures without the use of chemical fertilizers.© 2021 The Author(s).

Soil salinity is the major abiotic stress that disrupts nutrient uptake, hinders plant growth, and threatens agricultural production. Plant growth-promoting rhizobacteria (PGPR) are the most promising eco-friendly beneficial microorganisms that can be used to improve plant responses against biotic and abiotic stresses. In this study, a previously identified B. thuringiensis PM25 showed tolerance to salinity stress up to 3 M NaCl. The Halo-tolerant Bacillus thuringiensis PM25 demonstrated distinct salinity tolerance and enhance plant growth-promoting activities under salinity stress. Antibiotic-resistant Iturin C (ItuC) and bio-surfactant-producing (sfp and srfAA) genes that confer biotic and abiotic stresses were also amplified in B. thuringiensis PM25. Under salinity stress, the physiological and molecular processes were followed by the over-expression of stress-related genes (APX and SOD) in B. thuringiensis PM25. The results detected that B. thuringiensis PM25 inoculation substantially improved phenotypic traits, chlorophyll content, radical scavenging capability, and relative water content under salinity stress. Under salinity stress, the inoculation of B. thuringiensis PM25 significantly increased antioxidant enzyme levels in inoculated maize as compared to uninoculated plants. In addition, B. thuringiensis PM25-inoculation dramatically increased soluble sugars, proteins, total phenols, and flavonoids in maize as compared to uninoculated plants. The inoculation of B. thuringiensis PM25 significantly reduced oxidative burst in inoculated maize under salinity stress, compared to uninoculated plants. Furthermore, B. thuringiensis PM25-inoculated plants had higher levels of compatible solutes than uninoculated controls. The current results demonstrated that B. thuringiensis PM25 plays an important role in reducing salinity stress by influencing antioxidant defense systems and abiotic stress-related genes. These findings also suggest that multi-stress tolerant B. thuringiensis PM25 could enhance plant growth by mitigating salt stress, which might be used as an innovative tool for enhancing plant yield and productivity.

Increased incidence of abiotic stresses impacting adversely plant growth and productivity in major crops is being witnessed all over the world. Therefore, as a result of such stress factors, plant growth under the stress conditions will be less than the non-stress conditions. Growing concerns and global demand for correct, environmentally-friendly techniques exist to reduce the adverse effects of plant stress. Under such stressful conditions, the role of interactions of plant and beneficial microorganisms is of great significance. Application of plant growth promoting rhizobacteria (PGPRs) is a useful option to decrease these stresses and is now widely in practice. Plants inoculated with PGPRs induce morphological and biochemical modifications resulting in increased tolerance to abiotic stresses defined as IST (induced systemic tolerance). PGPRs increase plant growth and resistance to abiotic stresses through various mechanisms (more than one mechanism of action) such as production of ACC (1-aminocyclopropane-1-carboxylate) deaminase, reducing production of stress ethylene, modifications in phytohormonal content, induction of synthezing plant antioxidative enzymes, improvement in the uptake of essential mineral elements, extracellular polymeric substance (EPS) production, decrease in the absorbtion of excess nutrients/heavy metals, and induction of abiotic stress resistance genes. Experimental evidence also suggests that stimulated plant growth by these bacteria is the net result of various mechanisms of action that are activated simultaneously. In this review paper, we reviewed the action mechanisms through which PGPRs could alleviate abiotic stresses (salinity, drought, heavy metal toxicity, and nutritional imbalance) in plants. Use of PGPRs is predicted to become a suitable strategy and an emerging trend in sustainable enhancement of plant growth. Generally, ACC deaminase and IAA-producing bacteria can be a good option for optimal crop production and production of bio-fertilizers in the future due to having multiple potentials in alleviating stresses of salinity, drought, nutrient imbalance, and heavy metals toxicity in plants. This review paper also emphasizes future research needs about the combined utilization of stress tolerant-PGPRs with multiple plant growth promoting (PGP) characteristics under environmental stresses.Copyright © 2018 Elsevier Inc. All rights reserved.

Understanding the primary mechanisms for plant promotion under salt stress with plant growth promoting rhizobacteria (PGPR) inoculation of different salt-tolerant plant groups would be conducive to using PGPR efficiently. We conducted a meta-analysis to evaluate plant growth promotion and uncover its underlying mechanisms in salt-sensitive plants (SSP) and salt-tolerant plants (STP) with PGPR inoculation under salt stress. PGPR inoculation decreased proline, sodium ion (Na+) and malondialdehyde but increased plant biomass, nutrient acquisition (nitrogen, phosphorus, potassium ion (K+), calcium ion (Ca2+), and magnesium ion (Mg2+)), ion homeostasis (K+/Na+ ratio, Ca2+/Na+ ratio, and Mg2+/Na+ ratio), osmolytes accumulation (soluble sugar and soluble protein), antioxidants (superoxide dismutase), and photosynthesis (chlorophyll, carotenoid, and photosynthetic rate) in both SSP and STP. The effect size of total biomass positively correlated with the effect sizes of nutrient acquisition and the homeostasis of K+/Na+, and negatively correlated with the effect size of malondialdehyde in both SSP and STP. The effect size of total biomass also positively correlated with the effect sizes of carotenoid and the homeostasis in Ca2+/Na+ and Mg2+/Na+ and negatively correlated with the effect size of Na+ in SSP, but it only negatively correlated with the effect size of Ca2+ in STP. Our results suggest that the plant growth improvement depends on the nutrient acquisition enhancement in both SSP and STP, while ion homeostasis plays an important role and carotenoid may promote plant growth through protecting photosynthesis, reducing oxidative damage and promoting nutrient acquisition only in SSP after PGPR inoculation under salt stress.

Salt-tolerant plant growth-promoting rhizobacteria (PGPR) can improve soil enzyme activities, which are indicators of the biological health of the soil, and can overcome the nutritional imbalance in plants. A pot trial was executed to evaluate the effect of inoculation of different salt-tolerant PGPR strains in improving soil enzyme activities. Three different salinity levels (original, 5, and 10 dS m–1) were used and maize seeds were coated with the freshly prepared inocula of ten different PGPR strains. Among different strains, inoculation of SUA-14 (Acinetobacter johnsonii) caused a maximum increment in urease (1.58-fold), acid (1.38-fold), and alkaline phosphatase (3.04-fold) and dehydrogenase (72%) activities as compared to their respective uninoculated control. Acid phosphatase activities were found to be positively correlated with P contents in maize straw (r= 0.96) and grains (r= 0.94). Similarly, a positive correlation was found between alkaline phosphatase activities and P contents in straw (r= 0.77) and grains (r= 0.75). In addition, urease activities also exhibited positive correlation with N contents in maize straw (r= 0.92) and grains (r= 0.91). Moreover, inoculation ofAcinetobacter johnsoniicaused a significant decline in catalase (39%), superoxide dismutase (26%) activities, and malondialdehyde contents (27%). The PGPR inoculation improved the soil’s biological health and increased the uptake of essential nutrients and conferred salinity tolerance in maize. We conclude that the inoculation of salt-tolerant PGPR improves soil enzyme activities and soil biological health, overcomes nutritional imbalance, and thereby improves nutrient acquisition by the plant under salt stress.

\n Soil salinity exert negative impacts on agricultural production and regarded as a crucial issue in global wetland rice production (\n Oryza sativa\n L.). Indigenous salt-tolerant plant growth-promoting rhizobacteria (\n Bacillus sp\n.) could be used for improving rice productivity under salinity stress. This study screened potential salt-tolerant plant growth-promoting rhizobacteria (PGPR) collected from coastal salt-affected rice cultivation areas under laboratory and glasshouse conditions. Furthermore, the impacts of these PGPRs were tested on biochemical attributes and nutrient contents in various rice varieties under salt stress. The two most promising PGPR strains, i.e., ‘UPMRB9’ (\n Bacillus tequilensis\n 10b) and ‘UPMRE6’ (\n Bacillus aryabhattai\n B8W22) were selected for glasshouse trial. Results indicated that ‘UPMRB9’ improved osmoprotectant properties, i.e., proline and total soluble sugar (TSS), antioxidant enzymes like superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT). Moreover, ‘UPMRB9’ inoculated rice plants accumulated higher amount of nitrogen and calcium in tissues. Therefore, the indigenous salt-tolerant PGPR strain ‘UPMRB9’ could be used as a potential bio-augmentor for improving biochemical attributes and nutrient uptake in rice plants under salinity stress. This study could serve as a preliminary basis for future large-scale trials under glasshouse and field conditions.\n

【目的】为获得耐盐植物促生菌，从甘肃景泰一处盐碱地中的植物根系中分离出多株耐盐菌，其中部分耐盐菌具有明显的植物促生特性。【方法】在前期研究基础上，选取1株耐盐菌W-1和盐敏感植物红豆草（Onobrychis viciaefolia）为试验材料，对菌株W-1的物种分类、耐盐、耐酸碱能力和植物促生特性进行检测，并探究其对不同浓度NaCl处理下红豆草生长和生理特性的影响。【结果】耐盐菌W-1为革兰氏阳性菌、产芽孢、无荚膜、有鞭毛，16S rDNA测序及比对结果显示，菌株W-1为暹罗芽孢杆菌（Bacillus siamensis）。菌株W-1对NaCl最高耐受度为13%，pH耐受范围为4.5-8.5。菌株W-1具有溶磷、解钾、固氮、产铁载体、产吲哚-3-乙酸（indole-3-acetic acid, IAA）和1-氨基环丙烷-1-羧酸（1-aminocyclopropane-1-carboxylic acid, ACC）脱氨酶活性等多种植物促生功能。接种菌株W-1可显著提高红豆草的干重、鲜重，促进其根系生长。在100和150 mmol/L NaCl胁迫下，接种W-1可显著增加红豆草可溶性糖、可溶性蛋白、脯氨酸和叶绿素含量以及过氧化氢酶活力，降低过氧化氢含量以及叶片黄化率和死亡率，减缓盐胁迫对红豆草生长的不利影响。【结论】W-1是一株具有耐盐、耐酸碱的优良植物促生菌，可增强豆科牧草的耐 盐性。

【目的】对玫瑰红球菌NB1菌株进行耐盐、促生特性研究，分析其全基因组信息，并挖掘NB1菌株的耐盐促生基因。【方法】利用形态学观察和16S rRNA基因序列分析对NB1菌株进行鉴定。利用固氮菌改良阿须贝氏培养基、Pikovaskaia's培养基、DF液体培养基和ADF液体培养基对NB1菌株的固氮、溶磷以及产ACC脱氨酶能力进行鉴定。将NB1菌株分别接种至盐浓度为0%、5%、10%、15%的NB固体培养基上，培养48 h后确定菌株的可耐受浓度。将经NB1菌株处理和未处理的玉米种子分别接种至1/2 MS培养基上，连续培养15 d后测定其株高、根长、鲜重与根重。以盆栽试验的形式，在同一盐浓度胁迫下，分别测量施加NB1菌液和未处理的玉米幼苗的生长指标。利用Illumina二代测序和PacBio三代测序对NB1菌株进行全基因分析。【结果】NB1菌株鉴定为玫瑰红球菌Rhodococcus rhodochrous，能产生ACC脱氨酶，具有固氮、溶磷等能力，可耐受5%的盐浓度，无土培养条件下，经NB1菌株处理后的玉米幼苗其株高、根长、鲜重和根重均显著增加，盆栽种植后，施加NB1菌液的玉米幼苗株高、鲜重显著高于CK。NB1菌株共编码基因5 259个，编码基因总长度5 230 674 bp，平均GC含量为68.30%。在NR、Pfam、COG、Swiss-Prot、GO、KEGG数据库分别注释到基因5 235、4 379、4 195、3 758、3 263个、2 449个。NB1菌株中有178个基因编码的蛋白质结构属于CAZy家族，内含几丁质酶、蔗糖酶等酶的基因。同时，预测NB1菌株中有14个次级代谢产物基因簇、457个毒力因子、324个耐药基因，且从NB1基因组内发现具有耐盐、促生特性的四氢嘧啶、四环素类抗生素等相关基因。【结论】玫瑰红球菌NB1具有耐盐促生特性，对玉米有一定的促生效果，为植物耐盐促生菌剂提供了新的菌种资源。