Combined proteomics, metabolomics and physiological analyses of rice growth and grain yield with heavy nitrogen application before and after drought

Background Nitrogen application can effectively mitigate the damage to crop growth and yield caused by drought. However, the efficiency of heavy nitrogen application before drought (NBD) and heavy nitrogen application after drought (NAD) to regulate rice response to drought stress remains controversial. In this study, we profiled physiology, proteomics and metabolomics in rice variety Wufengyou 286 of two nitrogen management modes (NBD and NAD) to investigate their yield formation and the mechanism of nitrogen regulation for drought resistance. Results Results revealed that the yield of NBD and NAD decreased significantly when it was subjected to drought stress at the stage of young panicle differentiation, while the yield of NBD was 33.85 and 36.33% higher than that of NAD in 2017 and 2018, reaching significant levels. Under drought conditions, NBD increased chlorophyll content and net photosynthetic rate in leaves, significantly improved the activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase and catalase, and decreased malondialdehyde (MDA) content compared with NAD. NBD promoted nitrogen assimilation in leaves, which was characterized by increased activities of nitrate reductase (NR) and glutamine synthetase (GS). In addition, NBD significantly increased the contents of osmotic regulatory substances such as soluble sugar, soluble protein and free proline. Gene ontology and KEGG enrichment analysis of 234 differentially expressed proteins and 518 differential metabolites showed that different nitrogen management induced strong changes in photosynthesis pathway, energy metabolism pathway, nitrogen metabolism and oxidation-reduction pathways. Conclusion Different nitrogen management methods have significant differences in drought resistance of rice. These results suggest that heavy nitrogen application before drought may be an important pathway to improve the yield and stress resistance of rice, and provide a new ecological perspective on nitrogen regulation in rice.

Different micro-climate response of indica rice population to nitrogen fertilizer

Field experiment was carried out from 2014 to 2016 to clarify the micro-climate response of indica rice population to nitrogen fertilizer. R498, R816 and R499 were used as representatives of drooping panicle, semi-erect panicle and erect panicle indica rice, respectively and 3 nitrogen fertilizer levels (N0 – 0 kg N/ha; N1 – 150 kg N/ha; N2 –150 kg/ha) were set for each panicle of indica rice. Results showed that the erect panicle indica rice (R499) improved the environment of temperature, relative humidity and light of rice population under heavy nitrogen fertilizer, and built a healthier micro-climate environment for rice population, especially at the middle position of rice population. Comparing with drooping panicle indica rice (R498), erect panicle indica rice performed better under heavy nitrogen fertilizer, with a higher micro-climate response index to nitrogen fertilizer at middle and lower position in rice population. In comparison of R498, the yield of R499 increased by 0.10–0.11 t/ha under N1 treatment, while it increased by 0.93–0.96 t/ha under N2 treatment; thus, the suggestion for farmers is to plant erect panicle indica rice in heavy fertilizer area or to use more fertilizer in moderate fertilizer area.

North Pacific-wide spreading of isotopically heavy nitrogen during the last deglaciation: Evidence from the western Pacific

Sedimentary δ15 N records in two IMAGES cores (MD012404 and MD012403) retrieved from the Okinawa Trough (OT) in the western North Pacific reveal deglacial increases with two peaks occurring during the Bølling/Allerød and the Preboreal/early Holocene periods. These peaks are synchronous with previously reported δ15 N peaks in the Eastern Tropical North Pacific, although the amplitudes (from 3.8 to 5.8‰) are much smaller in the OT. Similar δ15 N values for the last glacial maximum and the late-Holocene observed by us at a site far from the present-day zones of water-column denitrification (WCD) indicate that the mean 15 N/14 N of nitrate in the upper ocean did not differ much between the two climate states. The accumulation rate of organic carbon and total sulfur content are used as indices of the local WCD potential. The results suggest that enhancement of global WCD rather than local denitrification should be responsible for the deglacial maxima of sedimentary δ15 N in the Okinawa Trough. Our data could provide additional constraints to better understand changes in nitrogen budget during the glacial to interglacial transition.