While global food demand and world population are rapidly growing, land potential for cropping is steadily declining due to various soil degradation processes, a major one of them being soil salinization. Currently, approximately 20% of total cropland and 33% of irrigated agricultural land are salinized as a result of poor agricultural practices and it is expected that by 2050, half of the croplands worldwide will become salinized. Thus, there is a real need to better understand soil salinization processes and to develop agricultural practices that will enable production of the needed amount of food to feed humanity, while minimizing soil salinization and other degradation processes. The major sources of solutes in agricultural environments are: (i) the soil itself, and the parent geological material; (ii) shallow and salt rich groundwater; and (iii) salt rich irrigation water. The salinization of soil is a combination of transport of solutes towards the root zone to replenish evaporation and transpiration and limited washing of the soil by rain or irrigation. Therefore, most salinized soils are present in arid and semi-arid environments where precipitation is low and evaporation is high. In this manuscript, examples of soil salinization processes from croplands around the world will be presented and discussed to bring attention to this important topic, to present the latest scientific insights and to highlight the gaps that should be filled, from both scientific and practical perspectives.

Soil salinization and sodification are common processes that particularly characterize drylands. These processes can be attributed either to natural conditions or anthropogenic activities. While natural causes include factors such as climate, lithology, topography, and pedology, human causes are mostly related to agricultural land-use, and specifically, to irrigated agriculture. The objective of this study was to thoroughly review this topic, while highlighting the major challenges and related opportunities. Over time, the extent of saline, sodic, and saline-sodic croplands has increased, resulting in accelerated land degradation and desertification, decreased agricultural productivity, and consequently jeopardizing environmental and food security. Mapping and monitoring saline soils is an important management tool, aimed at determining the extent and severity of salinization processes. Recent developments in advanced remote sensing methods have improved the efficacy of mapping and monitoring saline soils. Knowledge on prevention, mitigation, and recovery of soil salinity and sodicity has substantially grown over time. This knowledge includes advanced measures for salt flushing and leaching, water-saving irrigation technologies, precision fertilizer systems, chemical restoration, organic and microbial remediation, and phytoremediation of affected lands. Of a particular interest is the development of forestry-related means, with afforestation, reforestation, agroforestry, and silvopasture practices for the recovery of salt-affected soils. The forecasted expansion of drylands and aggravated drying of existing drylands due to climatic change emphasize the importance of this topic.

为了探究不同施肥模式对盐碱地饲用燕麦（Avena sativa L.）根际土壤微生物多样性的影响，本文设置盐碱地饲用燕麦‘甜燕1号’不施肥、施用常规肥和控释肥模式，基于16S rRNA和内转录间隔区（Internal transcribed spacer，ITS）基因高通量测序技术分别对根际土壤细菌和真菌多样性进行生物信息学分析。结果显示，施肥比不施肥模式增加了根际土壤细菌和真菌的α和β多样性，其中控释肥模式下细菌和真菌群落的操作性分类单元（Operational taxonomic unit，OTU）数量最高。3种施肥模式下优势细菌门均为放线菌门（Actinobacteria）和变形杆菌门（Proteobacteria），优势真菌门均为子囊菌门（Ascomycota）和担子菌门（Basidiomycota）。相关性分析表明，细菌和真菌的优势菌门相对丰度与pH值和全盐含量呈负相关关系，与土壤养分中的全磷含量相关性最高。综上，施肥改变了根际土壤细菌和真菌群落的多样性，且施控释肥比施常规肥提高了饲用燕麦根际土壤微生物多样性。研究结果可为盐碱地饲用燕麦施肥模式的选择提供理论支撑。

为了研究伊犁河谷不同藜麦品种对盐胁迫的生理响应、评价藜麦品种耐盐性，以NXSG56、NXSG85、HP9、GY3、QA13-9共5个藜麦品种为材料，分别用50、100、150、200、250、300、350、400 mmol·L^-1 NaCl溶液处理种子及幼苗，研究不同NaCl浓度对种子萌发、幼苗生长及生理指标的影响。结果表明，随NaCl浓度升高，藜麦种子发芽率、发芽势及幼苗地下部分干鲜重、叶片叶绿素含量、超氧化物歧化酶活性、胁迫初期叶片可溶性糖含量均呈先上升后下降趋势；幼苗叶片相对电导率、脯氨酸、丙二醛、Na⁺及后期叶片可溶性糖含量持续上升；地上部分干鲜重、纤维素及K⁺含量持续下降。说明各藜麦品种幼苗在受到NaCl胁迫时会通过提高渗透物质含量、增加根系吸收面积、增强超氧化物歧化酶活性等自我保护机制对抗盐胁迫。以上结果表明，NXSG85、NXSG56较其他品种耐盐，QA13-9对NaCl胁迫较敏感。

为探究青绿苔草(Carex leucochlora)对盐(NaCl)胁迫的生理适应机制，本试验以青绿苔草'四季’为材料，采用盆栽试验，研究不同浓度(0，50，100，200和300 mmol·L^-1)NaCl胁迫对其生长和生理特性的影响。结果表明：不同浓度NaCl胁迫对青绿苔草生长抑制作用不同。低浓度盐(50 mmol·L^-1)对青绿苔草生长影响不显著，但胁迫8 d以上，叶片相对电导率显著提高。高浓度盐(≥100 mmol·L^-1)显著抑制青绿苔草生长，随着盐浓度提高和胁迫时间的延长，青绿苔草叶片相对含水量、叶绿素含量呈下降趋势；枯叶率、叶片相对电导率、丙二醛(Malondialdehyde，MDA)含量则呈升高趋势；超氧化物歧化酶(Superoxide dismutase，SOD)和过氧化物酶(Peroxidase，POD)活性呈先升高后降低的趋势。根据主成分分析和生物量下降50%时盐浓度建立回归方程确定青绿苔草耐盐临界浓度为231.29 mmol·L^-1。综上，青绿苔草在低盐或短期高盐胁迫下，表现出一定的耐盐性。

Saline-alkali stress is a widespread adversity that severely affects plant growth and productivity. Saline-alkaline soils are characterized by high salt content and high pH values, which simultaneously cause combined damage from osmotic stress, ionic toxicity, high pH and HCO3−/CO32− stress. In recent years, many determinants of salt tolerance have been identified and their regulatory mechanisms are fairly well understood. However, the mechanism by which plants respond to comprehensive saline-alkali stress remains largely unknown. This review summarizes recent advances in the physiological, biochemical and molecular mechanisms of plants tolerance to salinity or salt- alkali stress. Focused on the progress made in elucidating the regulation mechanisms adopted by plants in response to saline-alkali stress and present some new views on the understanding of plants in the face of comprehensive stress. Plants generally promote saline-alkali tolerance by maintaining pH and Na+ homeostasis, while the plants responding to HCO3−/CO32− stress are not exactly the same as high pH stress. We proposed that pH-tolerant or sensitive plants have evolved distinct mechanisms to adapt to saline-alkaline stress. Finally, we highlight the areas that require further research to reveal the new components of saline-alkali tolerance in plants and present the current and potential application of key determinants in breed improvement and molecular breeding.

Under drought stress, abscisic acid (ABA) triggers closure of leaf cell pores called stomata, which are formed by two specialized cells called guard cells in plant epidermis. Two pathways downstream of ABA stimulate phosphorylation of the S-type anion channels SLAC1 (slow anion channel associated 1) and SLAH3 (SLAC1 homolog 3), which causes these channels to open, reducing guard cell volume and triggering stomatal closure. One branch involves OST1 (open stomata 1), a calcium-independent SnRK2-type kinase, and the other branch involves calcium-dependent protein kinases of the CPK (calcium-dependent protein kinase) family. We used coexpression analyses in Xenopus oocytes to show that the calcineurin B-like (CBL) calcium sensors CBL1 and CBL9 and their interacting protein kinase CIPK23 also triggered SLAC1 and SLAH3 opening. We analyzed whether regulation of SLAC1 opening by these different families of kinases involved the same or different sites on SLAC1 by measuring channel conductance of SLAC1 with mutations in the putative phosphorylation sites in the amino or carboxyl termini coexpressed with specific kinases in Xenopus oocytes. SLAC1 mutants lacking the OST1-phosphorylated site were still activated by CPK or by CBL/CIPK complexes. Phosphorylation and activation of SLAC1 by any of the kinases were inhibited by the phosphatase ABI1 (ABA insensitive 1), which is inactivated in response to ABA signaling. These findings identified CBL/CIPK complexes as potential regulators of stomatal aperture through S-type anion channels and indicated that phosphorylation at distinct sites enables SLAC1 activation by both calcium-dependent and calcium-independent pathways downstream of ABA. Copyright © 2014, American Association for the Advancement of Science.

Salt stress is one of the major environmental stresses limiting plant growth and productivity. To adapt to salt stress, plants have developed various strategies to integrate exogenous salinity stress signals with endogenous developmental cues to optimize the balance of growth and stress responses. Accumulating evidence indicates that phytohormones, besides controlling plant growth and development under normal conditions, also mediate various environmental stresses, including salt stress, and thus regulate plant growth adaptation. In this review, we mainly discuss and summarize how plant hormones mediate salinity signals to regulate plant growth adaptation. We also highlight how, in response to salt stress, plants build a defense system by orchestrating the synthesis, signaling, and metabolism of various hormones via multiple crosstalks.Copyright © 2020. Published by Elsevier Ltd.

The coastal saline-alkali soil in eastern China is an important reserve arable land resource. Adding exogenous organic material is an effective way to improve soil fertility and promote the conversion of saline-alkali soil to agricultural soil. In this study, a field plot experiment was used to investigate the influences of different organic materials (vinegar residue, VR; sewage sludge, SS; vermicompost, VC) on the reduction in salinity-alkalinity barrier factors, the accumulation of soil organic carbon (SOC), and the improvement in soil fertility in saline-alkali soil. The results indicated that applying different types of exogenous organic materials reduced soil electrical conductivity (EC) and pH, promoted SOC accumulation, and increased the barley yield. With the same application rate, VR application was more beneficial in reducing soil EC and pH, accumulating SOC, and increasing barley yield compared to SS and VC applications. In particular, the barley yield with VR application was higher than that with SS and VC applications by 18.4% and 26.6% on average, respectively, during the two-year experiment. Correlation and path analysis revealed that the barley yield was significantly negatively correlated with soil barrier factors (EC and pH), but EC in SS and VC-treated soils had an indirect negative effect on barley yield, while EC in VR-treated soil had a direct negative effect (−2.24). In addition, the direct (−4.46) and indirect (5.39) contributions of SOC to barley yield were higher with VR than those with SS and VC, while the direct contribution of soil aggregate to barley yield was lower with VR than that with SS and VC. Therefore, compared with SS and VC applications, VR application led to a fast reduction in soil barrier factors and the rapid accumulation of SOC, which were more beneficial for increasing barley yields in saline-alkali soil.

以新疆克拉玛依农业综合开发区新垦重盐渍土为研究对象,在滴灌条件下开展了盐生植物盐角草(Salicornia europaea)、盐地碱蓬(Suaeda salsa)和裸地（对照）处理的试验,通过测定植物地上生物量及植株和土壤中K+、Na+、Ca2+、Mg2+、Cl- 和 SO2-4含量及土壤总盐含量,评估种植盐生植物对重盐渍土盐分的影响。结果表明:灌溉条件下,盐角草和盐地碱蓬地上生物量分别为11 044.37 kg·hm-2和19 119.26 kg·hm-2,刈割后地上部分灰分盐分别为4 709.98 kg·hm-2和5 184.96 kg·hm-2;与种植期前相比,种植期后盐角草、盐地碱蓬和对照处理0～30 cm土层总盐分别下降了55.62%、32.98%和20.79%,盐角草和盐地碱蓬处理下降幅度均高于对照,30～60 cm土层盐角草和盐地碱蓬处理土壤总盐分别下降了21.82%和29.16%,而对照却上升了18.31%;盐角草和盐地碱蓬均对Na+、Cl-和SO2-4具有较强的摄取能力,尤其是对Cl-表现出更强的选择吸收倾向;盐角草和盐地碱蓬SO2-4含量基本相当,但盐角草Na+和Cl-含量分别是盐地碱蓬的2.33倍和2.22倍,盐角草对于Na+和Cl-的强积聚特征使其更适于对氯化物盐渍土的改良。在盐渍荒漠新垦地种植盐生植物,土壤脱盐效果明显。

With the increasing shortage of water resources, the current management of saline–alkali lands in semi-arid and arid areas has gradually transformed from “flooding irrigation with drainage” in the past to the combination of controlling regional water and salt balance, phytoremediation, and comprehensive utilization of halophyte resources. However, soil salinization caused by natural and anthropogenic factors has still been a major global environmental problem, which changes the chemical and physical properties of soil, deteriorates the quality of underground water, and decreases biodiversity, contributing to the loss of soil productivity and the succession of the halotolerant species. Euhalophytes, as the materials for phytoremediation, have been confirmed to be effective species in improving saline–alkali soils. They can redistribute salts in soil profile through the interaction of their desalinization potential and irrigation water leaching, thereby preventing secondary salinization and improving soil productivity for long-term reclamation of saline soil. In this review, the adaptation mechanisms of euhalophytes to saline soils are generalized from the views of morphological, physiological, and molecular aspects and evaluated for their potential to remediate saline soil through salt removal and promoting leaching. Euhalophytes can not only sequestrate salts inside the central vacuole of cells to tolerate higher salt stress by means of organ succulence, ion compartmentalization, and osmotic adjustment but facilitate water infiltration and salts leaching through root–soil interaction. The root system’s mechanical penetration increases soil porosity, decreases soil density, as well as stabilizes soil aggregates. Moreover, the suitability of phytoremediation in arid situations with low precipitation and non-irrigation and some agricultural practices need to be taken into account to avoid salts returning to the soil as forms of litter and deep tillage altering salt distribution. Hence, euhalophytes planting in semi-arid and arid areas should be evaluated from their adaptation, desalinization, and prospective commercial values, such as foods, biofuels, and medical development to alleviate soil secondary salinization crisis and enhance the productivity of arable agricultural land.