Oat has been gaining renewed interest due to its role in a healthy human diet, in animal feed, and as a source of high value compounds with industrial applications. Nitrogen fertilization and planting density are two of the most important crop management practices that affect the formation of yield components and final yield of oat. A 2 year 3 × 5 factorial field experiment was conducted to investigate the effects of nitrogen (N) fertilizer and planting density on the flag leaf photosynthetic characteristics, grain yield, and yield components under rainfed conditions. The experiment consisted of three sowing densities (60, 180, and 300 kg·ha⁻¹) and five nitrogen fertilizer rates (0, 45, 90, 135, and 180 kg·ha⁻¹). Results showed that the grain yield was significantly (p < 0.05) correlated with the leaf net photosynthesis rate (Pn), stomatal conductance (Gs), intercellular CO₂ concentration (Ci), transpiration rate (Tr), water-use efficiency (WUE), stomatal limitation value (Ls), chlorophyll content (SPAD value), leaf area index (LAI), panicle length, number of spikelets per panicle (NSP), number of grains per panicle (NGP), weight of grains per panicle (WGP), and 1000-kernel weight. Among the yield components, grain yield was driven by number of spikelets per panicle (NSP) and number of grains per panicle (NGP) at low (or high) planting density with low N supply, whereas, at high N supply, 1000-kernel weight was also an important factor for yield. Nitrogen fertilizer and sowing density had significant (p < 0.05) effects on the flag leaf photosynthetic characteristics, grain yield, and yield components of oat. The yield components increased and then decreased with the increase in nitrogen fertilizer, while they decreased with the increase in planting density. The maximum values (p < 0.05) of grain yield were observed in the nitrogen fertilization of 90 kg·ha⁻¹ and sowing density of 180 kg·ha⁻¹ treatment in both growing seasons, mainly contributing to the improved leaf photosynthesis traits (Pn, Gs, Tr, Ls, SPAD, and LAI). The combination of nitrogen fertilization of 90 kg·ha⁻¹ and sowing density of 180 kg·ha⁻¹ is suitable for oat production on a cool semiarid plateau or other agroecozones with similar environmental conditions.

The WRKY family is widely involved in the regulation of plant growth and stress response and is one of the largest gene families related to plant environmental adaptation. However, no systematic studies on the WRKY family in oat (Avena sativa L.) have been conducted to date. The recently published complete genome sequence of oat enables the systematic analysis of the AsWRKYs. Based on a genome-wide study of oat, we identified 162 AsWRKYs that were unevenly distributed across 21 chromosomes; a phylogenetic tree of WRKY domains divided these genes into three groups (I, II, and III). We also analyzed the gene duplication events and identified a total of 111 gene pairs that showed strong purifying selection during the evolutionary process. Surprisingly, almost all genes evolved after the completion of subgenomic differentiation of hexaploid oat. Further studies on the functional analysis indicated that AsWRKYs were widely involved in various biological processes. Notably, expression patterns of 16 AsWRKY genes revealed that the response of AsWRKYs were affected by stress level and time. In conclusion, this study provides a reference for further analysis of the role of WRKY transcription factors in species evolution and functional differentiation.

In oat production, the over-application of nitrogen (N) fertilizer in fields due to low N fertilizer use efficiency not only increases production costs but also causes environmental pollution. Currently, mining low N-tolerant oat varieties is an important way to promote sustainable agriculture. In this study, 30 oat varieties were grown in a seedling culture with two treatments of normal N (10 mM NH₄NO₃) and low N (1.25 mM NH₄NO₃), and the correlations between agronomic traits and plant N content and low N tolerance coefficients and indices were determined, which can be used as indicators for the evaluation of low N-tolerant oat varieties. Coefficient of variation, correlation analysis, principal component analysis, partial least-squares discrimination analysis, random forest analysis, least absolute shrinkage and selection operator regression and model evaluation, and membership function analysis were used for in-depth analysis of these indicators. Plant N content, root–crown ratio, and dry weight of aboveground plant parts were found to be important indicators of low N tolerance in oats. According to the membership function ranking of the 30 selected oat varieties, Jiayan 2, Qingyongjiu 035, and Qingyin 2 had strong tolerance to low N stress and Qingyongjiu 003, Qingyongjiu 021, and Qingyongjiu 016 had poor tolerance to low N stress. Thus, this study provides a reliable and comprehensive method for evaluating the low N tolerance of oat varieties as well as a reference for screening other low N-tolerant plants.

The GRAS protein family is involved in plant growth and development, plant disease resistance, and abiotic stress response. Although the GRAS protein family has been systematically studied and reported in many plants, it has not been reported in oat, an excellent foodstuff crop of Gramineae. We identified 90 AsGRAS genes and all of the AsGRAS genes were randomly distributed on 21 chromosomes with 6 tandem duplicated genes and 49 pairs of segmental duplications, which may be the main reason for the expansion of the GRAS gene family. According to the phylogenetic tree, 90 AsGRASs were classified into 10 distinct subfamilies. Gene structure revealed introns varying from zero to seven, and all genes have conserved motifs and GRAS structure domain. Protein–protein interaction and miRNA prediction analysis showed that AsGRAS proteins mainly interacted with GA signalling, cell division, etc., and that the AsGRAS genes were targeted by miRNA171. RNA-seq and qRT–PCR data showed that GRAS genes were expressed at different growth and developmental stages and under different abiotic stresses in oat, indicating the potential role of GRAS genes in promoting growth and stress tolerance in oat. Overall, our evolutionary and expression analysis of AsGRAS genes contributes to the elucidation of a theoretical basis for the GRAS gene family. Moreover, it helped reveal gene function and laid the foundation for future agricultural improvement of oats based on functional properties.

Elymus sibiricus plays a crucial role in ecological protection and animal husbandry. However, after many years of growth, the biomass of E. sibiricus decreases, and the plants degrade. Moreover, there is no good solution to the problem of degradation of Elymus sibiricus; the addition of nitrogen (N) and phosphorus (P) fertilizers is the primary measure of cultivation management to improve yield, so it is crucial to find the appropriate level of fertilization. This study performed a two-factor split-plot experiment, including four levels of N (0, 45, 60, and 75 kg·hm⁻²) and four levels of P (0, 60, 75, and 90 kg·hm⁻²), to investigate the effect of N and P fertilizers on yield, yield components, and photosynthesis characteristics of E. sibiricus. The results showed that the forage yield in 2017 was higher than in 2018. The forage yield in 2017 was highest at N₇₅P₀ with a value of 29,926 kg·hm⁻², and in 2018 it was highest at N₄₅P₀ and N₇₅P₀ with a value of 12,266 kg·hm⁻² and 12,233 kg·hm⁻², respectively, which demonstrates the large impact of year effects on the forage yield. All traits increased with the increase in N and P fertilizer application, but with excess fertilizer application, the photosynthesis was limited, leading to a slowdown in growth and a decrease in yield. In addition, under adequate N fertilization, the role of P fertilization was not significant (p > 0.05). N, P, and N × P can significantly (p < 0.05) affect the yield traits and forage yield of E. sibiricus. According to the PCA, it is clear that N fertilizer has the largest effect, and the growth capacity of degraded E. sibiricus grassland can be restored by adding 75 kg·hm⁻² of nitrogen fertilizer.

Nitrogen (N) application significantly increases tiller numbers and is accompanied by changes in endogenous hormone content. We treated seedlings of Festuca kirilowii—a perennial forage grass—with nitrogen, determined the endogenous hormone content in the tiller buds, and performed a transcriptome analysis. The application of N reduced GA₃, ABA, and 5-DS content and increased ZT and IAA content. By screening DEGs in the transcriptome results, we obtained DEGs annotated to 25 GO entries and 8 KEGG pathways associated with endogenous hormones. Most of these GO entries and KEGG pathways were associated with IAA, GA_S, and ABA. We conducted a validation analysis of hormone-related DEGs using qRT-PCR to demonstrate that nitrogen controls the content of endogenous hormones by regulating the expression of these DEGs, which further affects tillering in F. kirilowii.