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 amendments have been proposed as an effective way to enhance soil carbon stocks on degraded soils, particularly in dryland farming areas. Soil organic carbon (SOC) plays an important role in improving soil quality, and soil aggregates are known to be crucial in sequestering and protecting SOC. However, how aggregation and protection of SOC by aggregates respond to a single application of bentonite combined with maize straw remains unknown, especially in the sandy soil of a semi-arid region. A three-year field experiment with four treatments [no amendment (CK), maize straw amendment addition only (T1, 6 Mg ha⁻¹), bentonite amendment addition only (T2, 18 Mg ha⁻¹), and maize straw combined with bentonite amendment (T3, 6 Mg ha⁻¹ maize straw plus 18 Mg ha⁻¹ bentonite)] was conducted in the Loess Plateau of China to assess the effects of bentonite and maize straw on aggregation and SOC. The results indicated that soil bulk density decreased by 2.72–5.42%, and soil porosity increased by 3.38–8.77% with three years of T3 application, especially in the 20–40 cm layer, compared with CK. T3 increased the amount of C input, SOC stock, and SOC stock sequestration rate by 1.04 Mg ha⁻¹ y⁻¹, 0.84–1.08 Mg ha⁻¹, and 0.49 Mg ha⁻¹ y⁻¹, respectively, and it increased the mass proportions and aggregate-associated C stock of >0.25 mm aggregates by 1.15–2.51- and 1.59–2.96-fold compared with CK. Correlation analysis showed a positive correlation of total SOC stock with the C concentration of >2 mm, 0.25–2 mm, and 0.053–0.25 mm aggregates. Aggregates of various sizes in sandy soils have the potential for greater SOC stock. Our findings suggest that the application of maize straw (6 Mg ha⁻¹) combined with bentonite (18 Mg ha⁻¹) would be an effective management strategy to enhance the bulk soil C pools by improving the soil structure and thereby improving soil fertility.

Oats are an important grain-feeding crop with strong saline–alkali tolerance; however, the genetic mechanism of this tolerance is not clear, which hinders the development of oat varieties adapted to saline soils. In this study, the saline–alkali tolerance of 524 oat germplasm resources was comprehensively evaluated using culture-dish germination and field identification methods. During the germination period, saline–alkali stress significantly inhibited the germination potential, germination rate, and shoot and root lengths of oat germplasm. The indicators decreased by 71.15%, 49.32%, 59.03%, and 63.90%, respectively. The relative value of each trait was used as the evaluation metric. The 524 oat germplasm resources were classified into five groups by cluster analysis, and 174 oat germplasm resources with saline-alkali tolerance at the germination stage were screened. A regression equation for the identification of germinated saline-alkali-tolerant oat germplasm resources under the same conditions was also established. The field experiment showed that the coefficients of variation of oat germplasm resources were 4.03–54.12% and 6.97–38.50% in the two locations, which was rich in genetic variation; the correlation analysis showed that the biological yield was positively correlated with the D-value, and 18 high–quality and high-yielding saline–alkali-tolerant oat germplasm resources were identified by combining the saline–alkali-tolerant and weak germplasm resources of the two locations. Based on the multidimensional evaluation of germination and field performance, the 18 saline–alkali–tolerant germplasms screened in this study provide high–quality germplasm resources and a theoretical basis for saline oat cultivation and saline-tolerant breeding.