The improvement of saline-alkali land plays a key role in ensuring food security and promoting agricultural development. Saline soils modifies the response of the soil microbial community, but research is still limited. The effects of applying phosphogypsum with rice cultivation (PRC) on soil physicochemical properties and bacterial community in soda saline-alkali paddy fields in Songnen Plain, China were studied. The results showed that the PRC significantly improved the physicochemical properties of soil, significantly reduced the salinity, increased the utilization efficiency of carbon, nitrogen, and phosphorus, and significantly increased the activities of urease and phosphatase. The activities of urease and phosphatase were significantly correlated with the contents of total organic carbon and total carbon. A redundancy analysis showed that pH, AP, ESP, HCO3−, and Na+ were dominant factors in determining the bacterial community structure. The results showed that PRC could improve soil quality and enhance the ecosystem functionality of soda saline-alkali paddy fields by increasing nutrient content, stimulating soil enzyme activity, and regulating bacterial community improvement. After many years of PRC, the soda-alkali soil paddy field still develops continuously and healthily, which will provide a new idea for sustainable land use management and agricultural development.

Alkaline stress with high pH levels could significantly influence plant growth and survival. The enzyme 9-cis-epoxycarotenoid dioxygenase (NCED) serves as a critical bottleneck in the biosynthesis of abscisic acid (ABA), making it essential for regulating stress tolerance. Here, we show that OsNCED3-overexpressing rice lines have increased ABA content by up to 50.90% and improved transcription levels of numerous genes involved in stress responses that significantly enhance seedling survival rates. Overexpression of OsNCED3 increased the dry weight contents of the total chlorophyll, proline, soluble sugar, starch, and the activities of antioxidant enzymes of rice seedlings, while reducing the contents of O2·−, H2O2, and malondialdehyde under hydroponic alkaline stress conditions simulated by 10, 15, and 20 mmol L−1 of Na2CO3. Additionally, the OsNCED3-overexpressing rice lines exhibited a notable increase in the expression of OsNCED3; ABA response-related genes OsSalT and OsWsi18; ion homeostasis-related genes OsAKT1, OsHKT1;5, OsSOS1, and OsNHX5; and ROS scavenging-related genes OsCu/Zn-SOD, OsFe-SOD, OsPOX1, OsCATA, OsCATB, and OsAPX1 in rice seedling leaves. The results of these findings suggest that overexpression of OsNCED3 upregulates endogenous ABA levels and the expression of stress response genes, which represents an innovative molecular approach for enhancing the alkaline tolerance of rice seedlings.

Modifying saline–alkali soil is crucial for ensuring food security and expanding arable land. Microorganisms play a key role in driving various biochemical processes in agricultural ecosystems. However, limited information exists on the changes in the microbial community and soil structure in soda saline-alkali soil under modified conditions. In this study, we examined the changes in soil physicochemical properties of saline–alkali soil altered by rice planting alone and by combined application of phosphogypsum in the Songnen Plain. The results demonstrated that phosphogypsum significantly improved the soil’s physicochemical properties; it notably reduced salinity and alkalinity while enhancing nutrient structure. Additionally, the utilization efficiency of carbon (C), nitrogen (N), and phosphorus (P) increased. Fungal community diversity also significantly improved, influenced mainly by soil water content (SWC), total organic carbon (TOC), soil organic matter (SOM), total nitrogen (TN) and sodium ion (Na+). TOC, SOM, TN, ESP, and Na+ served as the primary drivers affecting the fungal community. Our findings indicate that combining rice planting with phosphogypsum application effectively modifies saline–alkali soil, regulates fungal community structure, and enhances long-term soil health. Furthermore, the beneficial effects of phosphogypsum on saline–alkali soil persist for persists for several years, largely owing to its role in promoting microbial community growth.

The plant hormone abscisic acid (ABA) regulates the plant response to environmental stress; therefore, ABA priming is an effective strategy for enhancing stress tolerance in rice. In this study, we investigated the priming effects of 1 and 5 µM ABA on the biochemical and physiological traits associated with seedling growth performance in two rice cultivars exposed to saline (100 mM NaCl) and alkaline (15 mM Na2CO3) stress via root drenching. ABA pretreatment effectively reduced damage in rice seedlings by mitigating the increases in Na+/K+ ratio, membrane injury, contents of Na+, malondialdehyde, hydrogen peroxide, and superoxide anion radical, and prevented reductions in K+ and total chlorophyll contents, and ROS-related enzyme activities in both cultivars under saline and alkaline stresses. Rice seedlings with ABA pretreatment under alkaline stress had a stronger ability to maintain ion homeostasis, eliminate ROS, and induce changes in endogenous ABA levels via the upregulation of OsHKT1;5, OsSOS1, OsNHX5, OsPOX1, OsCATA, OsNCED3, OsSalT, and OsWsi18 and downregulation of OsRbohA than under saline stress. The saline–alkaline (SA)-sensitive cultivar demonstrated greater sensitivity to the priming effect of ABA than that of the SA-tolerant cultivar under both stress conditions. These findings have implications for rice adaptation to SA soils.

We aimed to determine the optimal combination of amendments to increase rice yields in saline-sodic soil. The effects of different proportions of phosphogypsum (P), farmyard fertilizer (F), and wood peat (W) across the main growth period of rice were studied. A total of 14 treatments were designed based on the “3414” fertilizer effect field experiment scheme, with 3 factors (P, F, and W) and 4 application levels per factor. Application of a combination of P, F, and W reduced soil pH and electrical conductance (EC) (p < 0.05), increasing rice yields. The theoretical rice yield after treatment P2F2W2 (P 30, F 50, and W 30 t·ha−1) was 5819.20 kg·ha−1, which was 32.52-fold higher than that after P0F0W0 (P, F, and W, 0 t·ha−1). Panicle weight, number of total filled grains, total grain weight, and seed-setting rate were 9.76, 17.35, 32.11, and 3.96 times higher than those in the control treatment, respectively. Compared with the control P0F0W0 treatment, soil pH in P2F2W2 in 0–5, 5–10, 10–15, and 15–20 cm depth decreased by 12.69, 12.32, 11.18, and 10.70%, respectively, and soil EC was 1.06-fold, and 70.79, 49.30, and 47.76% higher, respectively. Overall, we found that the P2F2W2 treatment, with a combination of P, 29.09–32.38 t·ha−1; F, 40.36–46.97 t·ha−1; and W, 19.57–23.95 t·ha−1 was optimal in this experiment.

Saline–alkaline (SA) stress is characterized by high salinity and high alkalinity (high pH), which severely inhibit plant growth and cause huge losses in crop yields worldwide. Here we show that a moderate elevation of endogenous abscisic acid (ABA) levels by RNAi-mediated suppression of OsABA8ox1 (OsABA8ox1-kd), a key ABA catabolic gene, significantly increased tolerance to SA stress in rice plants. We produced OsABA8ox1-kd lines in two different japonica cultivars, Dongdao 4 and Nipponbare. Compared with non-transgenic control plants (WT), the OsABA8ox1-kd seedlings accumulated 25.9%–55.7% higher levels of endogenous ABA and exhibited reduced plasmalemma injury, ROS accumulation and Na+/K+ ratio, and higher survival rates, under hydroponic alkaline conditions simulated by 10, 15, and 20 mmol L−1 of Na2CO3. In pot trials using SA field soils of different alkali levels (pH 7.59, 8.86, and 9.29), OsABA8ox1–kd plants showed markedly higher seedling survival rates and more vigorous plant growth, resulting in significantly higher yield components including panicle number (85.7%–128.6%), spikelets per panicle (36.9%–61.9%), branches (153.9%–236.7%), 1000–kernel weight (20.0%–28.6%), and percentage of filled spikelets (96.6%–1340.8%) at harvest time. Under severe SA soil conditions (pH = 9.29, EC = 834.4 μS cm−1), OsABA8ox1-kd lines showed an 194.5%–1090.8% increase in grain yield per plant relative to WT plants. These results suggest that suppression of OsABA8ox1 to increase endogenous ABA levels provides a new molecular approach for improving rice yield in SA paddies.

Soil alkalization triggers ion toxicity and osmotic and alkaline (high pH) stresses in plants, damaging their growth and productivity. Therefore, we investigated whether priming with abscisic acid (ABA) increases the tolerance of alfalfa seedlings to alkaline stress, and then examined the underlying molecular mechanisms. Alfalfa seedlings were pretreated with ABA (10 μM) for 16 h and then subjected to alkaline stress using a 15 mM Na2CO3 solution (pH 10.87). Compared with the control, ABA pretreatment significantly alleviated leaf damage and improved the fresh weight, water content, and survival rate of alfalfa seedlings under alkaline conditions. Abscisic acid pretreatment reduced accumulation of reactive oxygen species (ROS), increased activities of the antioxidant enzymes superoxide dismutase (SOD) and peroxidase (POD), maintained higher ratios of K+/Na+, Ca2+/Na+, and Mg2+/Na+, and increased accumulation of proline. In addition, ABA upregulated the expression of genes involved in proline biosynthesis (P5CS) and the sequestration of Na+ in vacuoles (NHX1 and AVP) under alkaline conditions. Abscisic acid priming increased tolerance to alkaline stress by maintaining homeostasis of ROS and metal ions and upregulating osmoprotection and the expression of stress tolerance-related genes.

Soil alkalization severely limits plant growth and development, however, the mechanisms of alkaline response in plants remain largely unknown. In this study, we performed physiological and transcriptomic analyses using two alfalfa cultivars (Medicago sativa L.) with different sensitivities to alkaline conditions. The chlorophyll content and shoot fresh mass drastically declined in the alkaline-sensitive cultivar Algonquin (AG) following alkaline treatment (0-25 mM Na2CO3 solution), while the alkaline-tolerant cultivar Gongnong NO.1 (GN) maintained relatively stable growth and chlorophyll content. Compared with AG, GN had higher contents of Ca2+ and Mg2+; the ratios of Ca2+ and Mg2+ to Na+, proline and soluble sugar, as well as higher enzyme activities of peroxidase (POD) and catalase (CAT) under the alkaline conditions. Furthermore, transcriptomic analysis identified three categories of alkaline-responsive differentially expressed genes (DEGs) between the two cultivars: 48 genes commonly induced in both the cultivars (CAR), 574 genes from the tolerant cultivar (TAR), and 493 genes from the sensitive cultivar (SAR). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that CAR genes were mostly involved in phenylpropanoid biosynthesis, lipid metabolism, and DNA replication and repair; TAR genes were significantly enriched in metabolic pathways, such as biosynthesis of amino acids and secondary metabolites including flavonoids, and the MAPK signaling pathway; SAR genes were specifically enriched in vitamin B6 metabolism. Taken together, the results identified candidate pathways associated with genetic variation in response to alkaline stress, providing novel insights into the mechanisms underlying alkaline tolerance in alfalfa.

Current indices of saline-alkaline (SA) tolerance are mainly based on the traditional growth and physiological indices for salinity tolerance and likely affect the accuracy of alfalfa tolerance predictions. We determined whether the inclusion of soil alkalinity-affected indices, particularly Ca2+, Mg2+, and their ratios to Na+ in plants, based on the traditional method could improve the prediction accuracy of SA tolerance in alfalfa, determine important indices for SA tolerance, and identify suitable alfalfa cultivars in alkaline salt-affected soils. Fifty alfalfa cultivars were evaluated for their SA tolerance under SA and non-SA field conditions. The SA-tolerance coefficient (SATC) for each investigated index of the alfalfa shoot was calculated as the ratio of SA to non-SA field conditions, and the contribution of SATC under different growth and physiological indices to SA tolerance was quantified based on the inclusion/exclusion of special alkalinity-affected indices. The traditional method, excluding the special alkalinity-affected indices, explained nearly all of the variation in alfalfa SA tolerance, and the most important predictor was the SATC of stem length. The new method, which included these special alkalinity-affected indices, had similar explanatory power but instead identified the SATC of shoot Ca2+/Na+ ratio, followed by that of stem length, as key markers for the field evaluation of SA tolerance. Ca2+, Mg2+, and their ratios to Na+ hold promise for enhancing the robustness of SA-tolerance predictions in alfalfa. These results encourage further investigation into the involvement of Ca2+ in such predictions in other plant species and soil types under more alkaline salt-affected conditions.

Abscisic acid (ABA) has been shown to prime rice seedlings for enhanced tolerance to alkaline stress under both greenhouse and field conditions. This study aimed to understand the mechanism of the ABA priming effect.