In the context of the increasingly serious issues of resource waste, soil degradation, and environmental pollution caused by excessive nitrogen fertilizer application worldwide, this study conducted a two-year field experiment in Qinghai Province to explore suitable nitrogen fertilizer management strategies for the region. Ten fertilization levels were set, incorporating varying ratios of conventional nitrogen fertilizer and organic fertilizer, as well as the proportion of base fertilizer and topdressing. The focus was on monitoring the forage yield, quality, and related physiological indicators of oats during the flowering and milk stages. The use of correlation analysis and the multi-criteria decision-making model TOPSIS was applied for comprehensive data evaluation to determine the optimal fertilization strategy. After systematic data collection and analysis, the results showed that when 75% conventional nitrogen fertilizer was combined with 4500 kg·hm⁻² of organic fertilizer (F4), the oat yield during the milking stage reached its peak at 14,722.48 kg·hm⁻². Additionally, the yield effect was optimal (13,677.34 kg·hm⁻²) when using 30% base fertilizer and 70% jointing fertilizer (D2). Regarding nutritional quality, the fertilization strategy combining 75% conventional nitrogen fertilizer with 4500 kg·hm⁻² of organic fertilizer, along with 30% base fertilizer and 70% jointing fertilizer (F4D2), significantly reduced the content of acid detergent fiber (ADF), neutral detergent fiber (NDF), and coarse fiber (CF) in oats, while increasing the content of EE (crude fat) and CP (crude protein). This significantly improved the nutritional value of oats. Correlation analysis further revealed the positive effect of fertilization amount and fertilization period on oat yield, as well as a negative correlation with fiber content. Finally, through comprehensive evaluation using the multi-criteria decision-making model TOPSIS, we verified the superiority of the fertilization strategy.

Nitrogen (N) plays a crucial role in forage yield. However, excessive application of N fertilizers in agricultural production not only increases the production cost but also leads to serious environmental problems. Therefore, mining low-N tolerant oat germplasm is important for the sustainable development of grass and pasture. Relevant physiological indices of five oat germplasm were measured and analyzed in the seedling leaves under low-nitrogen culture conditions, aiming to identify important physiological indices suitable for screening low-nitrogen-tolerant oat and to rank the low-nitrogen-tolerance ability of each oat variety. The results showed that the physiological indexes of oats under low-nitrogen conditions were significantly different from those under normal culture conditions, and the total root length, total nitrogen, photosynthesis index, and NR enzyme activity of leaves in the five oat germplasm showed a decreasing trend, while the proline, MDA, SOD, POD, and GS enzyme activities showed an increasing trend, but the magnitude of changes in the physiological indexes varied among different varieties. By analyzing the physiological indexes, the photosynthetic index and antioxidant enzyme activities were found to be important in assessing the ability of oats to tolerate low nitrogen and therefore can be used as important indexes for screening oats for low nitrogen tolerance. The results of the comprehensive analysis showed that the order of low-N tolerance of each variety was as follows: Qingyongjiu 035> Jiayan No.2> Qingyin No.2> ZNY255> ZNY256, and the results of the present study provide a reference for the further large-scale screening of low-N-tolerant oat resources and the selection of varieties.

To evaluate the optimal substitution ratio of organic fertilizer for chemical nitrogen fertilizer and its underlying mechanisms, a pot experiment was conducted in the rhizosphere soil of oat (Avena sativa) on the Qinghai–Tibet Plateau. Five treatments were established: CK (control), T1 (chemical fertilizer alone), T2 (100% organic fertilizer substitution for chemical nitrogen fertilizer), T3 (30% organic fertilizer substitution for chemical nitrogen fertilizer), and T4 (60% organic fertilizer substitution for chemical nitrogen fertilizer). We analyzed soil carbon fractions, microbial community structure, carbon-cycling enzyme activities, and yield responses and applied partial least squares–structural equation modeling (PLS-SEM) to identify key regulatory pathways. The results showed that 30% organic substitution (T3) was associated with optimized soil carbon pools, improved microbial community composition, and enhanced carbon-cycling enzyme activities, while reducing the abundance of potentially harmful fungi. Structural equation modeling indicated that β-glucosidase activity and the relative abundance of Proteobacteria were the primary drivers of yield, together explaining 76% of its variation. The ecosystem multifunctionality index (EMF) was significantly and positively correlated with yield. In summary, under the conditions of this experiment, 30% organic fertilizer substitution achieved a favorable balance between soil ecological functions and crop yield, providing a valuable reference for sustainable nutrient management in oat production in high-altitude cold regions.

Nitrogen limitation restricts plant growth, development, and yield in crops and forage species. Although TCP transcription factors are implicated in diverse abiotic-stress responses, the functions of most TCP genes in oat remain unclear. Here, we cloned and characterized the AsTCP38 gene, which is 1215 bp long and encodes a 405-amino-acid protein. The predicted protein contains a conserved TCP domain and shares its highest sequence similarity with Arabidopsis thaliana (A. thaliana) AtTCP15. The AsTCP38 protein localized to the nucleus, and promoter analysis identified cis-elements associated with light, hormone, and stress responses. We generated AsTCP38-overexpressing A. thaliana and wheat plants and screened an oat leaf yeast cDNA library for candidate interacting proteins. In these heterologous overexpression lines, AsTCP38 overexpression was associated with greater abscisic acid (ABA) sensitivity and improved seedling growth under low-nitrogen conditions. Changes in antioxidant-enzyme activities, nitrogen-metabolism-related enzyme activities, and endogenous hormone contents were also observed. Together, these findings suggest that AsTCP38 may participate in low-nitrogen responses and provide a basis for further functional studies in oat. Direct regulatory targets and the contribution of AsTCP38 to low-nitrogen adaptation in oat remain to be established.

Nitrogen deficiency limits oat growth and productivity, but the molecular basis of contrasting low-nitrogen responses among oat germplasms remains poorly understood. This study compared the low-nitrogen-tolerant germplasm Jiayan No.2 with the low-nitrogen-sensitive germplasm ZNY256 after 15 days of hydroponic cultivation under normal nitrogen (10 mM NH₄NO₃) or low nitrogen (1.25 mM NH₄NO₃). Growth traits, plant nitrogen content, nitrogen-metabolism-related enzyme activities, soluble sugar content, transcriptomes, and untargeted metabolomes were analyzed. Low nitrogen reduced plant height and plant nitrogen content in both germplasms, with more pronounced changes in ZNY256. Root length was unaffected, whereas root dry weight decreased only in ZNY256. ZNY256 also showed a larger transcriptional response than Jiayan No.2. Functional analyses highlighted phenylpropanoid and flavonoid biosynthesis, glutathione and nitrogen metabolism, ribosome biogenesis, and plant MAPK signaling. Metabolomic profiling identified changes in amino acid-, lipid-, secondary metabolite-, and antioxidant-related features. Integrated analysis and qRT-PCR validation further identified candidate genes associated with these responses. These findings characterize transcriptional and metabolic changes associated with the contrasting responses of the two oat germplasms to nitrogen deficiency and provide candidate genes, metabolites, and pathways for further investigation of low-nitrogen adaptation in oat.