Expression levels of nitrogen assimilation-related genes, physiological responses, and morphological adaptations of three indica rice (Oryza sativa L. ssp. indica) genotypes subjected to nitrogen starvation conditions

Toward Low-Emission Agriculture: Synergistic Contribution of Inorganic Nitrogen and Organic Fertilizers to GHG Emissions and Strategies for Mitigation

Nitrogen (N) and organic-source fertilizers in agriculture are important to sustain crop production for feeding the growing global population. However, their use can result in significant greenhouse gas (GHG) emissions, particularly carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), which are important climate drivers. This review discusses the interactive effects, uncovering both additive and suppressive outcomes of emissions under various soil and climatic conditions. In addition to examining the effects of nitrogen and the nitrogen use efficiency (NUE), it is crucial to comprehend the mechanisms and contributions of organic fertilizers to GHG emissions. This understanding is vital for developing mitigation strategies that effectively reduce emissions while maintaining agricultural productivity. In this review, the current knowledge is utilized for the management of nitrogen practices, such as the optimization of fertilization rates, timing, and methods of application, in terms of the nitrogen use efficiency and the related GHG emissions. Moreover, we discuss the role of organic fertilizers, including straw, manure, and biochar, as a mitigation strategy in relation to GHG emissions through soil carbon sequestration and enhanced nutrient cycling. Important strategies such as crop rotation, tillage, irrigation, organic fertilizers, and legume crops are considered as suitable approaches for minimizing emissions. Even with the progress made in mitigating fertilizer-related emissions, research gaps remain, specifically concerning the long-term effect of organic fertilizers and the interactions between microbial communities in the soil and fertilization practices. Furthermore, the differences in application practices and environmental conditions present considerable obstacles to accurate emission quantification. This review underlines the importance of conducting more thorough research on the combined application of N and organic fertilizers in multiple cropping systems to evolve region-specific mitigation strategies.

Mining and identification of factors influencing multi-branch plasticity in ornamental kale

MAIN CONCLUSION

Transcriptome-revealed plant hormones and nutrients are key factors influencing branching in ornamental kale. Topping treatment and exogenous hormones application revealed that auxin and SLs inhibited lateral buds outgrowth, respectively. Plant architecture is a crucial horticultural characteristic in ornamental kale as the variety of branching patterns significantly enhances the esthetic appeal of garden plants. The factors influencing multi-branch plasticity in ornamental kale are yet to be elucidated. In this study, we mined the key branching genes by comparing the transcriptomes of a single-branched inbred line 'P29' and its natural multi-branched mutant, revealing a total of 3727 differentially expressed genes (DEGs) between them. A Kyoto Encyclopedia of Genes and Genome enrichment analysis identified 41 auxin-related DEGs, 5 strigolactones (SLs)-related DEGs, 12 cytokinin-related DEGs, 3 abscisic acid-related DEGs, and 1 gibberellin-related DEG. Nutrients, such as sugar, nitrogen, and phosphorus, might also influence branching. To investigate the effects of auxin and SLs on branch outgrowth, we conducted a topping treatment (removed rosette head) and externally applied the SL analog GR24 and corresponding SL biosynthesis inhibitor TIS108 to the single-branch inbred line 'P23'. GR24 effectively inhibited lateral bud outgrowth while TIS108 promoted lateral bud initiation. This work provides a novel perspective of the multi-branch plasticity in ornamental kale and also highlights potential key elements regulating plant morphology, which could be targeted to improve the architecture of valuable plant species.

Auxin synthesis promotes N metabolism and optimizes root structure enhancing N acquirement in maize (Zea mays L.)

MAIN CONCLUSION

Foliar NAA increases photosynthate supplied by enhancing photosynthesis, to strengthen root activity and provide a large sink for root carbohydrate accumulation, which is beneficial to acquire more nitrogen. The improvement of grain yield is an effective component in the food security. Auxin acts as a well-known plant hormone, plays an important role in maize growth and nutrient uptake. In this study, with maize variety Zhengdan 958 (ZD958) as material, the effects of auxin on nitrogen (N) uptake and assimilation of seedling maize were studied by hydroponic experiments. With water as the control, naphthalene acetic acid (NAA, 0.1 mmol/L) and aminoethoxyvinylglycine (AVG, 0.1 mmol/L, an auxin synthesis inhibitor) were used for foliar spraying. The results showed that NAA significantly improved photosynthetic rate and plant biomass by 58.6% and 91.7%, respectively, while the effect of AVG was opposite to that of NAA. At the same time, key enzymes activities related N assimilation in NAA leaves were significantly increased, and the activities of nitrate reductase (NR), glutamine synthetase (GS) and glutamate synthase (GOGAT) were increased by 32.3%, 22.9%, and 16.2% in new leaves. Furthermore, NAA treatment promoted underground growth. When compared with control, total root length, root surface area, root tip number, branch number and root activity were significantly increased by 37.8%, 22.2%, 35.1%, 28.8% and 21.2%. Root growth is beneficial to N capture in maize. Ultimately, the total N accumulation of NAA treatment was significantly increased by 74.5%, as compared to the control. In conclusion, NAA foliar spraying increased endogenous IAA content, and enhanced the activity of N assimilation-related enzymes and photosynthesis rate, in order to build a large sink for carbohydrate accumulation. In addition, NAA strengthened root activity and regulated root morphology and architecture, which facilitated further N uptake and plant growth.