Biochar application to soil is widely recognized as a promising agricultural management practice to increase crop production by enhancing the physical, chemical, and microbiological properties of the soil. Despite the fact that numerous studies have investigated biochar production and alterations in soil properties, the effects of biochar on contrasting soils within the same region remain poorly understood, especially for semi-arid regions. Therefore, a three-year field experiment was initiated in 2020 wherein biochar was applied once to a buckwheat field at rates of 0, 20, 40, and 60 Mg ha⁻¹ (BC0: no biochar; BC1: 20 Mg ha⁻¹; BC2: 40 Mg ha⁻¹; BC3: 60 Mg ha⁻¹) for two soil types (aeolian sandy and grey meadow soil) in the northeast of Inner Mongolia, China. The soil water storage (SWS), nutrient contents (organic matter, available nitrogen, phosphorus, and potassium), microbial biomass (carbon, nitrogen, and phosphorus), and enzyme activities (urease, invertase, and alkaline phosphatase) were assessed at a soil depth of 0–15 cm as part of the soil quality assessment, and the buckwheat grain yield was estimated for crop productivity evaluation. The results showed that biochar amendment improved selected soil physicochemical and microbiological properties and buckwheat yields for both soil types. Compared to BC0, the biochar addition increased buckwheat yields, on average, by 11.23% to 22.82% in aeolian sandy soil and by 7.36% to 14.87% in grey meadow soil across three years. The results of principal component analysis (PCA) and random forest analysis (RFA) indicate that soil available nutrients and microbiological properties were the most important factors influencing buckwheat yields in aeolian sandy soil and grey meadow soil, respectively. Based on RFA, the available potassium, phosphorus, and nitrogen were found to contribute at rates of 13.10%, 10.06%, and 8.12%, respectively, to buckwheat yields in aeolian sandy soil. In contrast, alkaline phosphatase, urease, and microbial biomass carbon contribute 20.26%, 8.48%, and 7.82%, respectively, to the buckwheat yields in grey meadow soil. Following biochar addition, there was greater improvement in soil health and buckwheat production for aeolian sandy soil than grey meadow soil. In conclusion, biochar addition is an effective practice for improving soil health and crop productivity in both aeolian sandy soil and grey meadow soil in semi-arid regions.

Biochar (BC) application is widely recognized as a promising strategy for enhancing soil fertility; however, its lasting effects on microbial communities in aeolian sandy soils of semi-arid regions remain poorly understood. To fill this knowledge gap, we conducted a field experiment to evaluate long-term changes in soil properties and microbial community structure in a buckwheat cropping system, 4 years after a single application of biochar (BC) at rates of 0 (BC0), 20 (BC1), 40 (BC2), and 60 (BC3) Mg ha⁻¹ in aeolian sandy soils of Inner Mongolia, China. Results revealed significant improvements in soil pH, moisture content, organic carbon (SOC), and available nutrients, as well as microbial biomass and enzyme activity, particularly at higher BC application rates (BC2 and BC3). SOC increased by 9.42% (BC2) and 14.13% (BC3). BC application altered microbial community composition, with minimal effects on bacterial diversity but reduced fungal diversity. Enhanced soil C and N cycling was linked to shifts in key microbial genera, while relative abundances of potential pathogens such as Fusarium and Nothophoma declined by up to 58 and 77%, respectively. Mantel tests confirmed significant correlations between shifts in microbial diversity and community composition and changes in soil properties, with particularly strong associations for fungal diversity related to SOC (r = 0.50, p < 0.001) and microbial biomass carbon (SMC; r = 0.43, p < 0.001). Redundancy analysis further revealed that bacterial communities were significantly associated (p < 0.05) with pH, microbial biomass nitrogen (SMN), and invertase activity, while fungal communities were linked to pH, microbial biomass phosphorus (SMP), and urease activity. This study underscores the potential of biochar to enhance soil health by improving soil fertility, reshaping microbial community composition, and suppressing soil-borne pathogens, particularly at higher application rates. These findings provide valuable insights for the reclamation of degraded sandy soils in semi-arid regions on a global scale.

Stem rust, caused by Puccinia graminis f. sp. avenae (Pga) Eriks. and E. Henn., is a worldwide and harmful disease of oat (Avena sativa L.). Currently, no resistant varieties are used in production as the molecular resistance mechanism of oat to stem rust remains unclear. Here, oat plants were inoculated with Pga pathogens, and the metabolome and transcriptome of leaves were detected to investigate the molecular and physiological changes. Our results showed that Pga inoculation increased the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and phenylalnine ammonialyase (PAL), which triggered defense responses. The transcriptomic and metabolomic analyses were performed to detect the key genes and metabolites of oat interacting with Pga. We identified 1814 upregulated and 1955 downregulated genes in Pga infected leaves. These genes were mainly involved in the ‘phenylpropanoid biosynthesis’, ‘flavonoid biosynthesis’, and ‘photosynthesis-antenna proteins’. We also detected 162 differential metabolites between Pga-infected and non-infected leaves, including flavonoids and derivatives, amino acids, organic acids, and carbohydrates. The integrated analysis revealed four pathways, including the ‘citrate cycle’, ‘cysteine and methionine metabolism’, ‘tryptophan metabolism’, and ‘glyoxylate and dicarboxylate metabolism’. The networks for these pathways were subsequently constructed. Overall, the results suggested that oat plants fight against Pga by activating the metabolism of amino acids, organic acids, and flavonoids. This study provides valuable molecular information about the response of oat to Pga infection.

The oat is a crop and forage species with rich nutritional value, capable of adapting to various harsh growing environments, including dry and poor soils. It plays an important role in agricultural production and sustainable development. However, the molecular mechanisms underlying the responses of oat to drought stress remain unclear, warranting further research. In this study, we conducted a pot experiment with the drought-resistant cultivar JiaYan 2 (JIA2) and water-sensitive cultivar BaYou 9 (BA9) during the booting stage under three water gradient treatment conditions: 30% field capacity (severe stress), 45% field capacity (moderate stress), and 70% field capacity (normal water supply). After 7 days of stress, root samples were collected for transcriptome and proteome analyses. Transcriptome analysis revealed that under moderate stress, JIA2 upregulated 1086 differential genes and downregulated 2919 differential genes, while under severe stress, it upregulated 1792 differential genes and downregulated 4729 differential genes. Under moderate stress, BA9 exhibited an upregulation of 395 differential genes, a downregulation of 669, and an upregulation of 886 differential genes, and it exhibited 439 downregulations under severe stress. Under drought stress, most of the differentially expressed genes (DEGs) specific to JIA2 were downregulated, mainly involving redox reactions, carbohydrate metabolism, plant hormone signal regulation, and secondary metabolism. Proteomic analysis revealed that in JIA2, under moderate stress, 489 differential proteins were upregulated and 394 were downregulated, while 493 differential proteins were upregulated and 701 were downregulated under severe stress. In BA9, 590 and 397 differential proteins were upregulated under moderate stress, with 126 and 75 upregulated differential proteins under severe stress. Correlation analysis between transcriptomics and proteomics demonstrated that compared with no drought stress, four types of differentially expressed proteins (DEPs) were identified in the JIA2 differential gene–protein interaction network analysis under severe stress. These included 13 key cor DEGs and DEPs related to plant hormone signal transduction, biosynthesis of secondary metabolites, carbohydrate metabolism processes, and metabolic pathways. The consistency of gene and protein expression was validated using qRT-PCR, indicating their key roles in the strong drought resistance of JIA2.

Drought deficit inhibits oat growth and yield. Fulvic acid (FA) can enhance plant stress tolerance, but its effects on regulating the ascorbate–glutathione cycle, chlorophyll synthesis, and carbon–assimilation ability remain unclear. Therefore, this study aimed to elucidate the physiological mechanisms of the FA regulation of drought tolerance in oats and its relationship with growth and yield using the drought-resistant variety Yanke 2 and the drought-sensitive variety Bayou 9. The effects of FA on growth and yield, the antioxidant system, chlorophyll synthesis, and carbon–assimilation capacity of oats under drought stress were investigated by systematically assessing changes in morphogenesis, ascorbate–glutathione cycle, chlorophyll and its intermediates, carbon–assimilation enzyme activities, and carbohydrate metabolism. The results showed that under drought stress, FA treatment significantly promoted oat growth (leaf area, dry matter) and yield, elevated glutathione peroxidase, ascorbate peroxidase, glutathione reductase, and dehydroascorbate reductase activities, reduced ascorbic acid, and reduced glutathione content. In addition, FA increased chlorophyll, as well as magnesium protoporphyrin IX, protoporphyrin IX, and protochlorophyllin acid ester content, enhanced 1,5-bisphosphate ribulose carboxylase, 1,5-bisphosphate ribulose carboxylase enzyme, 1,7-bisphosphate sestamibiose heptulose esterase, 1,6-bisphosphate fructose aldolase, sucrose synthase, sucrose phosphate synthase, acid invertase, and neutral invertase activities, and increased sucrose, glucose, and fructose content. Overall, fulvic acid (FA) alleviates drought-induced damage in oats by enhancing the ascorbate–glutathione cycle, promoting chlorophyll biosynthesis, and improving carbon assimilation and carbohydrate metabolism. The drought-sensitive variety (Yanke 2) was more effective in application compared to the drought-resistant variety (Bayou 9). This research provides valuable insight into its potential as a biostimulant under abiotic stress.

Soil salinity is among the crucial factors influencing agricultural productivity of crops, including oat. The respiratory metabolic pathways are of great significance for plants to adapt to salt stress, but current research is limited and there are few reports on salt-tolerant crops such as oat, which is necessary to conduct in-depth research. In this study, we conducted a pot experiment to determine the effects of salt stress on oat root growth and respiratory metabolism. Three salt stress levels—control (CK), moderate, and severe—were applied to compare the salt tolerance of the salt-tolerant cultivar Bai2 and the salt-sensitive cultivar Bai5. We selected oat roots at the seedling stage as the research focus and analyzed fresh root samples using an Oxytherm liquid-phase oxygen electrode, a digital scanner, and proteomics. The results showed that with an increased concentration of salt stress, the dry and fresh weight, root–shoot ratio, total root length, root surface area, root volume, and average diameter of the two oat cultivars showed a decreasing trend. Compared with CK, the total root respiration rate of Bai2 under moderate and severe stress decreased by 15.6% and 28%, respectively, and that of Bai5 decreased by 70.4% and 79.0%, respectively. After quantitative analysis of 18 oat root samples from the 2 cultivars using the label-free method, 7174 differential proteins were identified and 63 differential proteins were obtained, which involved 7 functional categories. In total, 111 differential proteins were specifically expressed in the root of the salt-tolerant cultivar Bai2, involving 12 functional categories. Through interaction network analysis, the proteins differentially expressed between the salt treatment and CK groups of the salt-tolerant cultivar Bai2 were analyzed. In total, five types of differentially expressed proteins interacting with each other were detected; these mainly involved antioxidant enzymes, pyruvate metabolism, glycolysis, tricarboxylic acid cycle, and energy metabolism pathways. Salt stress promoted the respiration rate of oat root glycolysis. The respiration rate of the tricarboxylic acid pathway decreased with increased salt stress concentration, while the respiration rate of the pentose phosphate pathway increased. Compared with CK, following moderate and severe salt stress treatment, alcohol dehydrogenase activity in Bai2 increased by 384% and 145%, respectively, while that of Bai5 increased by 434% and 157%, respectively. At increased salt stress concentrations, Bai2 mainly used pyruvate–ethanol fermentation for anaerobic respiration, while Bai5 mainly used pyruvate–lactic acid fermentation for anaerobic respiration. This significant discovery revealed for the first time from the perspective of respiratory metabolism that different salt-tolerant oat cultivars adapt to salt stress in different ways to maintain normal growth and development. The experimental results provide new insights into plant adaptation to salt stress from the perspective of respiratory metabolism.