Widely untargeted metabolomic profiling unearths metabolites and pathways involved in leaf senescence and N remobilization in spring-cultivated wheat under different N regimes.

Progression of leaf senescence consists of both degenerative and nutrient recycling processes in crops including wheat. However, the levels of metabolites in flag leaves in spring-cultivated wheat, as well as biosynthetic pathways involved under different nitrogen fertilization regimes, are largely unknown. Therefore, the present study employed a widely untargeted metabolomic profiling strategy to identify metabolites and biosynthetic pathways that could be used in a wheat improvement program aimed at manipulating the rate and onset of senescence by handling spring wheat (Dingxi 38) flag leaves sampled from no-, low-, and high-nitrogen (N) conditions (designated Groups 1, 2, and 3, respectively) across three sampling times: anthesis, grain filling, and end grain filling stages. Through ultrahigh-performance liquid chromatography-tandem mass spectrometry, a total of 826 metabolites comprising 107 flavonoids, 51 phenol lipids, 37 fatty acyls, 37 organooxygen compounds, 31 steroids and steroid derivatives, 18 phenols, and several unknown compounds were detected. Upon the application of the stringent screening criteria for differentially accumulated metabolites (DAMs), 28 and 23 metabolites were differentially accumulated in Group 1_vs_Group 2 and Group 1_vs_Group 3, respectively. From these, 1-O-Caffeoylglucose, Rhoifolin, Eurycomalactone;Ingenol, 4-Methoxyphenyl beta-D-glucopyranoside, and Baldrinal were detected as core conserved DAMs among the three groups with all accumulated higher in Group 1 than in the other two groups. Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed that tropane, piperidine, and pyridine alkaloid biosynthesis; acarbose and validamycin biosynthesis; lysine degradation; and biosynthesis of alkaloids derived from ornithine, lysine, and nicotinic acid pathways were the most significantly (p < 0.05) enriched in Group 1_vs_Group 2, while flavone and flavonol as well as anthocyanins biosynthetic pathways were the most significantly (p < 0.05) enriched in Group 1_vs_Group 3. The results from this study provide a foundation for the manipulation of the onset and rate of leaf senescence and N remobilization in wheat.

Fertilization treatments affect soil CO2 emission through regulating soil bacterial community composition in the semiarid Loess Plateau.

A growing body of literature have emphasized the effects of fertilization regimes on soil respiration and microbial community in the semiarid region, however, fertilization treatment effects on the soil CO2 emission, soil bacterial community, and their relationships from long-term experiments is lacking. In the present study, we investigated the effects of long-term fertilization regimes on soil bacterial community and thereafter on soil CO2 emission. A 9-year field experiment was conducted with five treatments, including no fertilizer (NA) and four fertilization treatments (inorganic fertilizer (CF), inorganic plus organic fertilizer (SC), organic fertilizer (SM), and maize straw (MS)) with equal N input as N 200 kg hm-2. The results indicated that CO2 emission was significantly increased under fertilization treatments compared to NA treatment. The bacterial abundance was higher under MS treatment than under NA treatment, while the Chao1 richness showed opposite trend. MS treatment significantly change soil bacterial community composition compared to NA treatment, the phyla (Alphaproteobacteria and Gammaproteobacteria) and potential keystone taxa (Nitrosomonadaceae and Beijerinckiaceae) were higher, while the Acidobacteriota was lower under MS treatment than under NA treatment. CO2 emission was positively correlated with the abundance of Alphaproteobacteria, Gammaproteobacteria, and keystone taxa, negatively correlated with these of Acidobacteriota. Random forest modeling and structural equation modeling determined soil organic carbon, total nitrogen, and the composition and network module III of the bacterial community are the main factors contribute to CO2 emission. In conclusion, our results suggest that the increased CO2 emission was affected by the varied of soil bacterial community composition derived from fertilization treatments, which was related to Alphaproteobacteria, Gammaproteobacteria, Acidobacteriota, and potential keystone taxa (Nitrosomonadaceae and Beijerinckiaceae), and highlight that the ecological importance of the bacterial community in mediating carbon cycling in the semiarid Loess Plateau.

Post-anthesis Relationships Between Nitrogen Isotope Discrimination and Yield of Spring Wheat Under Different Nitrogen Levels.

Wheat grain yield and nitrogen (N) content are influenced by the amount of N remobilized to the grain, together with pre-anthesis and post-anthesis N uptake. Isotopic techniques in farmed areas may provide insight into the mechanism underlying the N cycle. 15N-labeled urea was applied to microplots within five different fertilized treatments 0 kg ha-1 (N1), 52.5 kg ha-1 (N2), 105 kg ha-1 (N3), 157.5 kg ha-1 (N4), and 210 kg ha-1 (N5) of a long-term field trial (2003-2021) in a rainfed wheat field in the semi-arid loess Plateau, China, to determine post-anthesis N uptake and remobilization into the grain, as well as the variability of 15N enrichment in aboveground parts. Total N uptake was between 7.88 and 29.27 kg ha-1 for straw and 41.85 and 95.27 kg ha-1 for grain. In comparison to N1, N fertilization increased straw and grain N uptake by 73.1 and 56.1%, respectively. Nitrogen use efficiency (NUE) and harvest index were altered by N application rates. The average NUE at maturity was 19.9% in 2020 and 20.01% in 2021; however, it was usually higher under the control and low N conditions. The amount of 15N excess increased as the N rate increased: N5 had the highest 15N excess at the maturity stage in the upper (2.28 ± 0.36%), the middle (1.77 ± 0.28%), and the lower portion (1.68 ± 1.01%). Compared to N1, N fertilization (N2-N5) increased 15N excess in the various shoot portions by 50, 38, and 35% at maturity for upper, middle, and lower portions, respectively. At maturity, the 15N excess remobilized to the grain under N1-N5 was between 5 and 8%. Our findings revealed that N had a significant impact on yield and N isotope discrimination in spring wheat that these two parameters can interact, and that future research on the relationship between yield and N isotope discrimination in spring wheat should take these factors into account.

Transcriptome profiling reveals major structural genes, transcription factors and biosynthetic pathways involved in leaf senescence and nitrogen remobilization in rainfed spring wheat under different nitrogen fertilization rates.

The present study was undertaken to profile transcriptional changes in flag leaves between anthesis and end of grain filling stages of rainfed spring wheat cultivar under varying nitrogen (N) application rates: 0 kg/ha (NN), 52.5 kg/ha (LN), and 210 kg/ha (HN). A total of 4485 and 4627 differentially expressed genes (DEGs) were detected in LN and HN, respectively. The differential application of N altered several pathways; including plant hormone signal transduction, mitogen-activated protein kinase signaling pathway-plant, photosynthesis, phenylpropanoid biosynthesis and ATP-binding cassette transporters. Jasmonic acid, abscisic acid, salicylic acid and brassinosteroid related genes promoted leaf senescence in NN or LN, whereas auxin, gibberellin acid and cytokinins genes inhibited leaf senescence in HN. Major transcription factors: auxin/indole-3-acetic acid (AUX/IAA), no apical meristem (NAC) and WRKY expressed higher in either HN or LN than NN. The DEGs, pathways and transcription factors provide valuable insight for manipulation of leaf senescence and N remobilization in wheat.

Water and Nitrogen Coupling Increased the Water-Nitrogen Use Efficiency of Oilseed Flax.

Increasing water shortages and environmental pollution from excess chemical nitrogen fertilizer use necessitate the development of irrigation-nitrogen conservation technology in oilseed flax production. Therefore, a two-year split-plot design experiment (2017-2018) was conducted with three types of irrigation (I) levels (no irrigation (I0), irrigation of 1200 m3 ha-1 (I1200), and 1800 m3 ha-1 (I1800)) as the main plot and three nitrogen (N) application rates (0 (N0), 60 (N60) and 120 (N120) kg N ha-1) as the subplot in Northwest China to determine the effects of irrigation and N rates on oilseed flax grain yield, yield components, water-use efficiency (WUE), and N partial factor productivity (NPFP). The results show that I1800 optimized the farmland water storage and water storage efficiency (WSE), which gave rise to greater above-ground biomass. Under I1800, the effective capsule (EC) number increased significantly with increasing irrigation amounts, which increased significantly with increasing nitrogen application rate (0-120 kg ha-1). Both irrigation and nitrogen indirectly affect GY by affecting EC; the highest grain yield was observed at the I1800N60 treatment, which increased by 69.04% and 22.80% in 2017 and 2018 compared with the I0N0 treatment, respectively. As a result, both irrigation and N affect grain yield by affecting soil water status, improving above-ground biomass, and finally affecting yield components. In addition, I1800N60 also obtained a higher WUE and the highest NPFP due to a higher grain yield and a lower N application rate. Hence, our study recommends that irrigation with 1800 m3 ha-1 coupled with 60 kg N ha-1 could be a promising strategy for synergistically improving oilseed flax WUE, grain yield and yield components within this semi-arid region.