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PurposeThis study investigated the chemical and physical mechanisms associated with the movement of water and salt in saline-alkali soil amended with different types of biochar.Materials and methodsFour types of biochar were selected: ordinary laboratory-prepared biochar (BC), acidified biochar (HBC), particle size modified biochar (NBC), and composite modified biochar (HNBC). The physical and chemical properties of the biochar treatments were characterized. Vertical infiltration simulation tests were conducted to analyze the effects of modification on the adsorption and distribution of salt ions on biochar, and the soil water-stable macro-aggregates in saline-alkali soil.Results and discussionThe porous structure, specific surface area (SSA), micropore volume (VMIC), and H/C value were increased by acidification, particle size modification, and composite modification. Compared with BC, HBC and HNBC enhanced the O/C and (O+N)/C values, thereby increasing the hydrophilicity. The vertical infiltration tests showed that the depth of the soil wetting peak and cumulative infiltration were both higher than in the control (CK) after adding biochar, where HBC had the greatest water retention capacity. The modified biochar reduced the salt content and water-soluble Na+ content of the soil profile by increasing the soil water content and adsorbing Na+. The modified biochar promoted the formation and stabilization of soil water-stable macro-aggregates. Amending soil with HBC showed the greatest reduction in salt content and increased water-stable macro-aggregation.ConclusionsHBC improved the water retention and Na+ adsorption capacity of biochar. This enhanced the formation of soil water-stable macro-aggregates and improved the effects of biochar on saline-alkali soil by altering soil physical and chemical properties.

Background and aims Phosphorus (P) addition is considered key factor in soil organic carbon (SOC) cycle. The potential impact mechanisms of P addition on SOC stability and sequestration were explored in saline-alkali soil. Methods A 9-year field experiment was arranged in the Yellow River Delta, which included (i) CK, no fertilization; (ii) NK, N and K fertilizer application; (iii) NP1K and (iv) NP2K, NK plus 28 and 56 kg P ha −1  year −1 application, respectively. Results Compared with NK, the content of particulate OC (POC) was significantly increased by 29.9% and 26.8% in NP1K and NP2K treatments, respectively. The variation trend of aromatic-C and microbial biomass C (MBC) was similar to that of POC, which were positively corelated with SOC sequestration. Meanwhile, C and specific C mineralization rate (CMR, SCMR) were increased with P addition, which might be due to the decrease of carboxyl or amidogen-C. Moreover, owing to the increase in root biomass, SOC sequestration was significantly increased by more than 9.3% with P addition. Redundancy analysis further indicated that root biomass was the main factor in regulating SOC. While the CMR and SCMR were higher of NP2K treatment than those of NP1K treatment, this might result in SOC sequestration was no significant change between the two treatments. Conclusion Long-term low-level P fertilization is a preferable practice to increase POC, stable chemical composition and MBC, and then SOC sequestration. These findings provide important insights into how long-term different levels of P application regulate soil C cycling in saline-alkali paddy soil. Graphical abstract

We characterize here the saline‐alkaline soils composed of Na2CO3 and NaHCO3 in the Ganga floodplain and the peninsular basin using various chemical proxies and the isotopic composition of Sr. Abundance of saline‐alkaline soils in the Ganga floodplain and their higher solubility make them an important source of non‐chloride Na and other dissolved ions including Sr to the river waters. Inverse model based source apportionment of dissolved ions indicates ∼26%–71% of Na at the Ganga outflow is influenced by the saline‐alkaline soils; however, in some of the tributaries of the Ganga in the floodplain, for example, in the Gomti, this contribution exceeds 85%. The estimated silicate erosion rate by correcting for the saline‐alkaline soil contribution in the Ganga floodplain (∼5 tons km−2 yr−1) is less than one third of that of the Himalayan headwaters (16 tons km−2 yr−1) emphasizing the important role of physical erosion in controlling the chemical erosion in the mountain catchments compared to higher temperature and residence time in the floodplain. The silicate sourced dissolved fluxes from the floodplains are comparable to those from the Himalaya because of the vast drainage area of the floodplains and peninsular catchment. The findings of this study have direct relevance to studies on the determination of silicate weathering rates of not only the Ganga system, but also of other basins infested by saline‐alkaline soils such as the Columbia, the Colorado, the upper Rio Grande, the Missouri‐Mississippi river system, the Parana river, the Niger, the Nile, and the Orange. Plain Language Summary The saline‐alkaline soils containing Na2CO3 and NaHCO3 are present abundantly in the plain and peninsular drainages of the Ganga. Their higher solubility contribute significantly to the dissolved ions budget of the river waters which was earlier considered as the part of silicate weathering resulting in overestimation of silicate weathering and hence the CO2 consumption in the Ganga System. Chemical and isotopic characterisation of these salts in the Ganga system allowed us to estimate actual silicate weathering of the system and associated CO2 consumption impacting the carbon cycle. This study estimates three times higher silicate erosion rate in the mountainous catchment of the Ganga, 16 tons km−2 yr−1 compared to its plain catchment, ∼5 tons km−2 yr−1. This study puts the hotly debated topic of importance of mountain versus plain erosion of the Ganga on rest and emphasizes the role of higher physical erosion in contributing to the higher chemical erosion in the hilly terrain compared to higher temperature and residence times in the plain catchment. Key Points The Ganga Plain is infested by saline‐alkaline soils, Na2CO3 and NaHCO3 minerals If not corrected, they overestimate the silicate erosion rates (SERs) in the Ganga Basin SER in the Ganga Plain is one third of that in the Himalaya

Response of rhizosphere microbial community structure and co-occurrence patterns to liquid organic fertilizer in sunflower cropland was investigated. Moderate and severe saline-alkaline soils were treated with liquid organic fertilizer containing mainly small molecular organic compounds (450 g L–1) at a rate of 4500 L ha–1 year−1 over 2 years. Compared with the untreated soils, organic fertilizer treatment increased soil nutrient concentrations by 13.8–137.1% while reducing soil pH and salinity by 5.6% and 54.7%, respectively. Organic fertilizer treatment also improved sunflower yield, plant number, and plant height by 28.6–67.3%. Following organic fertilizer treatment, fungal α-diversity was increased, and the effects of salinity-alkalinity stress on rhizosphere microbial communities were alleviated. The relative abundances of some halotolerant microbes and phytopathogenic fungi were reduced in organic fertilizer-treated soils, in contrast to increases in the relative abundances of plant growth-promoting microbes and organic matter decomposers, such as Nocardioides, Rhizophagus, and Stachybotrys. Network analysis revealed that severe salinity-alkalinity stress stimulated cooperation among bacteria, while organic fertilizer treatment tended to stimulate the ecosystem functions of fungi with higher proportions of fungi-bacteria and fungi-fungi links. More keystone taxa (e.g., Amycolatopsis, Variovorax, and Gemmatimonas) were positively correlated with soil nutrient concentrations and crop yield-related traits in organic fertilizer-treated soils. Overall, liquid organic fertilizer amendment could attenuate the adverse effects of salinity-alkalinity stress on sunflower yield by improving soil quality and optimizing rhizosphere microbial community structure and co-occurrence patterns.

Aims Heilongjiang Province in China experiences extremely cold weather, and its soil is saline–alkaline. Salinity and alkalinity severely restrain the growth of maize. Although Trichoderma treatment has been extensively evaluated as a promising strategy to improve soil quality, its impact on the bacterial community and physiochemical properties of this soil type is unclear. Methods In the current study, different amounts of Trichoderma were used in field experiments in the Heilongjiang Province for two consecutive years. High-throughput sequencing was used to analyse the impact of Trichoderma on bacterial diversity in maize rhizosphere soils. Changes in root growth, crop yield, and soil physicochemical properties were also monitored. Results Treatment with Trichoderma increased the overall abundance of bacteria in soil and affected the bacterial community structure in the rhizosphere soil. It also significantly increased the relative abundance of beneficial bacterial genera, including Nitrospira and Sphingomonas . Bacteria from the genus Stenotrophomonas were identified exclusively in Trichoderma treatment groups. Pearson’s correlation analysis revealed that changes in soil bacterial community composition were closely related to soil characteristics such as the pH, organic matter, and total nitrogen, and were highly correlated with Trichoderma treatment. Trichoderma treatment increased crop yield by 4.87–12.41%. Conclusions These findings suggest that Trichoderma treatment remarkably improves enzyme activity and nutrient content in soil; optimizes the microecological environment of the rhizosphere soil of maize; alleviates bacterial community degeneration in saline–alkaline soil from cold-region; and promotes the growth of maize plants, ultimately increasing crop yield. Graphical abstract Relationships among bacterial diversity composition and soil and plant properties in the rhizosphere soil under Trichoderma treatments.

The quality of soil is essential for ensuring the safety and quality of agricultural products. However, soils contaminated with toxic metals pose a significant threat to agricultural production and human health. Therefore, remediation of contaminated soils is an urgent task, and humic acid (HA) with hydroxyapatite (HAP) materials was applied for this study in contaminated alkaline soils to remediate Cd, Pb, Cu, and Zn. Physiochemical properties, improved BCR sequential extraction, microbial community composition in soils with superoxide dismutase (SOD), peroxidase (POD), and chlorophyll content in plants were determined. Among the studied treatments, application of HAP-HA (2:1) (T7) had the most significant impact on reducing the active forms of toxic metals from soil such as Cd, Pb, Cu, and Zn decreased by 18.59%, 9.12%, 11.83%, and 3.33%, respectively, but HAP and HA had a minor impact on metal accumulation in Juncao. HAP (T2) had a beneficial impact on reducing the TC leaf/root of Cd, Cu, and Zn, whereas HAP-HA (T5) showed the best performance for reducing Cd and Cu in EF leaf/soil . HAP-HA (T5 and T7) showed higher biomass (57.3%) and chlorophyll (17.9%), whereas HAP (T4) showed better performance in POD (25.8%) than T0 in Juncao. The bacterial diversity in soil was increased after applying amendments of various treatments and enhancing metal remediation. The combined application of HAP and HA effectively reduced active toxic metals in alkaline soil. HAP-HA mixtures notably improved soil health, plant growth, and microbial diversity, advocating for their use in remediating contaminated soils.

PurposeAlkaline salinity constrains crop yield. Previously, we observed local adaptation of Arabidopsis thaliana to saline-siliceous soils (pH ≤ 7) and to non-saline carbonate soils. However, no natural population of A. thaliana was localized on saline-alkaline soils. This suggests that salinity tolerance evolved on saline-siliceous soils may not confer tolerance to alkaline salinity. This hypothesis was explored by addressing physiological and molecular responses to alkaline salinity of A. thaliana that differ in tolerance to either non-alkaline salinity or carbonate.MethodsA. thaliana native to saline-siliceous soils (high salinity, HS), non-saline carbonate soils (high alkalinity, HA), or soils with intermediate levels of these factors (medium saline-alkalinity, MSA) were cultivated in common gardens on saline-siliceous or saline-calcareous substrates. Hydroponics and irrigation experiments confirmed the phenotypes. The growth, mineral concentrations, proline content, osmotic potential, genetic variation distribution, and expression levels of selected genes involved in salinity and alkalinity tolerance were assessed.ResultsHS performed best on saline-siliceous soil and in hydroponics with salinity (pH 5.9). However, HS was more sensitive to saline-alkaline conditions than HA and MSA. The fitness under saline-alkaline conditions was ranked according to MSA > HA > HS. Under alkaline salinity, MSA best maintained ion homeostasis, osmotic balance, and higher expression levels of key genes involved in saline or alkaline tolerance (AHA1, root HKT1 and FRO2, and shoot NHX1 and IRT1).ConclusionIn A. thaliana, salinity tolerance evolved on saline-siliceous soils does not provide tolerance to alkaline salinity. Plants native to intermediate conditions (MSA) have more plasticity to adapt to alkaline salinity than those locally adapted to these individual stress factors.

Cotton ( Gossypium spp .) is a key crop in Kazakhstan, yet its productivity is constrained by saline-alkaline soils, which affect approximately 41% of the nation’s arable land. Conventional soil remediation methods are often unsustainable and economically impractical. This study investigates the potential of Bacillus megaterium PEF-1, a plant growth-promoting rhizobacterium (PGPR) isolated from cotton rhizospheres in the Turkestan region, as a biofertilizer for saline-alkaline conditions. The strain demonstrated high tolerance to salinity (up to 10% NaCl), alkalinity (pH 9.0), and heavy metals, and produced significant levels of indole-3-acetic acid (IAA; 895 mg/L in vitro). Field trials with seed inoculation (10⁹ CFU/mL) showed marked improvements in cotton growth, including increases in plant height (18%), boll number (22%), and yield (25%) relative to controls. Soil analyses revealed enhanced nutrient availability in treated plots: nitrogen (+ 4.3%), phosphorus (+ 15.1%), potassium (+ 26.8%), and humus content (+ 29.3%). Stress mitigation was achieved through ACC deaminase-mediated ethylene reduction and superoxide dismutase (SOD)-driven reactive oxygen species (ROS) scavenging. Acute toxicity tests, conducted in accordance with OECD guidelines, confirmed the strain’s biosafety with no adverse effects in mammalian models. Bacillus megaterium PEF-1 exhibits strong potential as a sustainable biofertilizer for improving cotton yields and soil fertility under saline-alkaline stress. Its capacity for nutrient mobilization, phytohormone synthesis, and abiotic stress alleviation aligns with the United Nations Sustainable Development Goals (SDGs) 2 (Zero Hunger) and 15 (Life on Land), offering a scalable, eco-friendly alternative to chemical fertilizers for arid and degraded agroecosystems.

Sweet sorghum ( Sorghum bicolor Moench) seedling emergence and growth are significantly impeded by physical soil crusts (PSCs) in saline-alkaline soils. Abscisic acid (ABA) is a potent seed priming agent known for modulating plant physiological and metabolic responses under salinity stress. However, the influence of ABA priming on seedling emergence in PSCs remains unclear. This study conducted both pot and field experiment to examine the effects of ABA priming on enhancing seedling emergence under PSC conditions. ABA priming altered the balance of at least 24 endogenous phytohormones, including abscisic acid, jasmonic acid, gibberellins, ethylene, auxins, and cytokinins. Additionally, it reprogrammed starch and sucrose metabolism, resulting in the differential expression of genes encoding key enzymes such as AMY, BAM, and INV, which are crucial for converting complex sugars into readily available energy sources, thereby supporting seedling growth. Furthermore, 52 differentially expressed metabolites (DEMs) of flavonoids were identified in germinating seedlings, including 15 anthocyanins, 3 flavones, 7 flavonols, 6 isoflavones, 7 flavanones, and 14 other flavonoids. Genetic and metabolic co-expression network analysis, along with flavonoid biosynthesis pathway exploration, revealed that the biosynthesis of 17 key DEMs—including liquiritigenin, apigenin, kaempferide, syringetin, phloretin, formononetin, dihydrokaempferol, and xanthohumol—was regulated by 10 differentially expressed genes (DEGs) associated with flavonoid biosynthesis. These DEGs encoded 7 enzymes critical for this pathway, including chalcone synthase, shikimate O-hydroxycinnamoyltransferase, bifunctional dihydroflavonol 4-reductase, naringenin 7-O-methyltransferase, and anthocyanidin reductase. This regulation, along with reduced levels of superoxide anion (O 2 − ) and malondialdehyde and increased antioxidant enzyme activities, suggested that flavonoids played a vital role in mitigating oxidative stress. These findings demonstrate that ABA priming can effectively enhance sweet sorghum seedling emergence in PSCs by accelerating emergence and boosting stress resistance.

The form of inorganic N in soil is governed by N transformations, but the relationship between the soil N transformation dynamics and the N uptake by plants is unclear. The effect of liming and nitrification inhibitor on crop N uptake efficiency (NUE) and N loss due to altered soil N processes was investigated using a 15 N tracing approach. Crops with different N uptake strategies (sweet potato (Dioscorea esculenta L.); an ammonium-N preferring plant and pakchoi (Brassica chinensis L.); a nitrate–N preferring plant) were grown in two agricultural soils with different pH values with or without lime and nitrification inhibitor (3,4-dimethylpyrazole phosphate, DMPP). We monitored the effects of 15 N-nitrate or 15 N-ammonium on the plant biomass and NUE, residual soil N, leachate, and emitted gas. The NUE of pakchoi in acidic soil was greater with nitrate than with ammonium; however, when lime was applied, the NUE of pakchoi increased significantly compared to ammonium alone. The NUE of pakchoi was not affected by N source in the alkaline soil, but application of DMPP together with ammonium significantly reduced NUE of pakchoi compared to ammonium alone. The N source had no effect on the NUE of sweet potato in acidic or alkaline soils, while NUE increased significantly after application of lime and ammonium (31.3%) and with application of DMPP (32.4%) compared to ammonium alone (30% in acidic soil and 23% in alkaline soil). Pakchoi NUE was significantly (p < 0.05) related to gross mineralization rate and the inorganic N supply capacity. Nitrous oxide emissions after N fertilization were greater in the alkaline than in acid soil greater after ammonium than after nitrate application. Since DMPP together with ammonium reduced N2O losses from the alkaline soil, this indicates the importance of nitrification as an N2O production process. Nitrate leaching was greater with lime and ammonium application compared to ammonium alone in the acidic soil, whereas the opposite occurred for ammonium leaching. In summary, crop NUE can be significantly increased by lime treatment whereas the addition of DMPP also increased the NUE of sweet potato, which prefer ammonium, grown in the alkaline soil.