Humic acid plays an important role in improving grain yield and reducing N losses. In order to explore the effects of humic acid added to controlled-release fertilizer on summer maize yield, nitrogen use efficiency (NUE) and the characteristics of greenhouse gas (GHG) emissions in maize farmland soil, a two-year field experiment was set up. The treatments consisted of two fertilizers: 3% humic acid added to controlled-release fertilizer (HACRF), controlled-release fertilizer (CRF) and a control (without N fertilizer, N0). The results demonstrate that the yield and NUE of summer maize were significantly increased with the addition of humic acid in N fertilizer. Compared with N0 and CRF, the yield of maize was increased by 99.1% and 5.0%, respectively. Compared with CRF, the contents of soil ammonium–nitrogen (NH₄⁺-N) and nitrate–nitrogen (NO₃⁻-N) in HACRF were higher during early maize growth stage but lower during the late grain-filling stage. The NUE and soil nitrogen interdependent rate of HACRF were significantly increased by 4.6–5.4% and 7.2–11.6%, respectively, across the years compared with those of CRF. Moreover, the annual cumulative N₂O emissions in HACRF were decreased by 29.0% compared with the CRF. Thus, the global warming potential and greenhouse emission intensity of HACRF were significantly decreased by 29.1% and 32.59%, respectively, compared with CRF. In conclusion, adding humic acid to controlled-release fertilizer can result in higher yield and nitrogen uptake, improve nitrogen use efficiency and reduce greenhouse gas emissions, which have better yield and environmental effects.

Background: Shade stress, a universal abiotic stress, suppresses plant growth and production seriously. However, little is known regarding the protein regulatory networks under shade stress. To better characterize the proteomic changes of maize leaves under shade stress, 60% shade (S) and supplementary lighting (L) on cloudy daylight from tasseling stage to physiological maturity stage were designed, the ambient sunlight treatment was used as control (CK). Isobaric tag for relative and absolute quantification (iTRAQ) technology was used to determine the proteome profiles in leaves. Results: Shading significantly decreased the SPAD value, net photosynthetic rate, and grain yield. During two experimental years, grain yields of S were reduced by 48 and 47%, and L increased by 6 and 11%, compared to CK. In total, 3958 proteins were identified by iTRAQ, and 2745 proteins were quantified including 349 proteins showed at least 1.2-fold changes in expression levels between treatments and CK. The differentially expressed proteins were classified into photosynthesis, stress defense, energy production, signal transduction, and protein and amino acid metabolism using the Web Gene Ontology Annotation Plot online tool. In addition, these proteins showed significant enrichment of the chloroplasts (58%) and cytosol (21%) for subcellular localization. Conclusions: 60% shade induced the expression of proteins involved in photosynthetic electron transport chain (especially light-harvesting complex) and stress/defense/detoxification. However, the proteins related to calvin cycle, starch and sucrose metabolisms, glycolysis, TCA cycle, and ribosome and protein synthesis were dramatically depressed. Together, our results might help to provide a valuable resource for protein function analysis and also clarify the proteomic and physiological mechanism of maize underlying shade stress.

Background: Exogenous 6-benzyladenine (6-BA) could improve leaf defense system activity. In order to better understand the regulation mechanism of exogenous 6-benzyladenine (6-BA) on waterlogged summer maize, three treatments including control (CK), waterlogging at the third leaf stage for 6 days (V3–6), and application of 100 mg dm^− 3 6-BA after waterlogging for 6 days (V3–6-B), were employed using summer maize hybrid DengHai 605 (DH605) as the experimental material. We used a labeling liquid chromatography-based quantitative proteomics approach with tandem mass tags to determine the changes in leaf protein abundance level at the tasseling stage. Results: Waterlogging significantly hindered plant growth and decreased the activities of SOD, POD and CAT. In addition, the activity of LOX was significantly increased after waterlogging. As a result, the content of MDA and H₂O₂ was significantly increased which incurred serious damages on cell membrane and cellular metabolism of summer maize. And, the leaf emergence rate, plant height and grain yield were significantly decreased by waterlogging. However, application of 6-BA effectively mitigated these adverse effects induced by waterlogging. Compared with V3–6, SOD, POD and CAT activity of V3–6-B were increased by 6.9, 12.4, and 18.5%, LOX were decreased by 13.6%. As a consequence, the contents of MDA and H₂O₂ in V3–6-B were decreased by 22.1 and 17.2%, respectively, compared to that of V3–6. In addition, the leaf emergence rate, plant height and grain yield were significantly increased by application of 6-BA. Based on proteomics profiling, the proteins involved in protein metabolism, ROS scavenging and fatty acid metabolism were significantly regulated by 6-BA, which suggested that application of 6-BA exaggerated the defensive response of summer maize at proteomic level. Conclusions: These results demonstrated that 6-BA had contrastive effects on waterlogged summer maize. By regulating key proteins related to ROS scavenging and fatty acid metabolism, 6-BA effectively increased the defense system activity of waterlogged summer maize, then balanced the protein metabolism and improved the plant physiological traits and grain yield.