Synergistic Mechanism Of Controlled-release Urea Combined With Biostimulant On Rice

Controlled-release urea(CRU),which are designed to regulate the release of N into the soil solution to matche the nutrient demands of the crop,can significantly increase the yields of crop with reduce cost,and it also has been treated as an ideal choice in dealing with low nitrogen utilization rate problem.Biostimulating hormone,with the ability in increasing the absorption and utilization of nutrients by plants and improving the tolerance of plants to abiotic stresses,has been considered as a guarantee for high quality and high yield of crops.The application of CRU or biostimulating hormone alone has been widely launced in sustainable agricultural for higher production,but its synergistic effects has rarely been studied.Particularly,the research on the exploitment of environmentally friendly and highly efficient biostimulating hormones has an fundenmental meaning for the development of sustainable agricultural.In this study,a novel bio-stimulant PVE(Paecilomyces variotii extracts)was extracted from the wild endophytic bacteria Paecilomyces variotii,and identified its chemical composition.A 2-year field experiment was conducted to study the effects of different dosages of PVE combined with CRU on the rice yield,yield components,nitrogen use efficiency and soil nutrient supply intensity with common urea application as a control,and determined the optimal dosage of PVE for field application;Next,a 2-year field experiment was conducted to study the optimal dosage of PVE combined with constant and reduced fertilization of CRU and common urea on rice yield,nitrogen use efficiency,dynamic changes of soil nutrient and economic benefits;Then the effects of PVE on germination rate,leaf photosynthetic characteristics,root morphology and oxidative damage of rice under low temperature stress were studied by indoor germination and liquid culture experiments;Transcriptome sequencing and real-time PCR were used to explore the mechanism of PVE in promoting the growth of rice.The main findings are listed below:(1)The extraction of PVE and its chemical structurePVE extracted from wild Seabuckthorn endophytic fungus Paecilomyces vannamei by fermentation is a biostimulating hormone with a molecular weight between 140-2507 Da.Spectroscopic characteristics results indicated that PVE contained more carbohydrate,amino acid,alkyl structure and less aromatic structure.(2)Effects of controlled-release urea combined with different dosages of PVE on rice yield,nitrogen utilization rate and economic benefitCRU have the ability with constant supply of N.The 2-year field experiment results showed that one-time basal application of CRU improved NO₃^-content by 37.11%and 39.77%,NH₄⁺content by 27.03%and 31.01%,rice yield by 6.90%and 21.01%,nitrogen utilization efficiency by 14.86%and 23.84%,and economic benefits by 7.21%and 26.88%,respectively.Besides,the rice growth can be affected by the application dosage of PVE,and the application of PVE at dosage of 750 mg/hm²combined with CRU on a 2-year field experiment further increased rice yield by 12.10%and 9.25%with increased effective tillering,nitrogen use efficiency by 15.04%and 16.36%,and average net profit by 15.43%and 11.62%,respectively,but have no effect on the content of available nutrients in soil.PVE is an ultra-high activity biostimulant,which has a good growth promotion effects at very low application dosage.However,with the increase of PVE dosage,the yield of rice decreased in spite of the yield is still higher than the application of CRU alone.(3)Effects of reduced nitrogen fertilizer combined with PVE on rice yield,nitrogen utilization rate and economic benefitField experiments results showed that the N release pattern fit with the demands of crop for nutrients and the correlation rate is upon 0.99.Under the same N application level,CRU improved rice yield,nitrogen use efficiency and economic benefits by the increase of effective tillering and grain number per panicle of rice,compared with common urea.When the CRU application amount is reduced by 40%,it still can improve rice yield by 8.10%and 7.09%,and the economic benefits by 14.14%and 12.38%,respectively,compared with full application rate of common urea.The application of PVE further increased rice yield when combined with CRU.The full application rate of CRU with PVE have the highest rice yield in the two years,and it improve rice yield by 9.25%and 8.67%,the nitrogen use efficiency by 16.36%and 20.22%and the net income by 11.62%and 10.90%,respectively,compared with the application of CRU alone.(4)Physiological regulation mechanisms of PVE on resistance of rice seedlings to low temperature stressIndoor germination and liquid culture experiments showed that PVE could break seed dormancy and promote seed germination in advance under low temperature(15?).With the PVE application,it increased the leaf biomass of rice seedlings,promoted the elongation of rice roots,and raised the root-shoot ratio significantly.Compared with the treatment without PVE,PVE significantly increased the leaf photosynthetic rate by 5.14?34.43%,the stomatal conductance by 7.85?16.16%,the transpiration rate by 34.04?65.18%,and decreased the intercellular CO₂ concentration by 9.00?18.30%.In the concentration range of 0.05-0.50?g/L,PVE also increased the activity of antioxidant enzymes in leaves and roots of rice seedlings,and reduced the MDA content of roots by 19.41?29.81%.PVE also reduced the accumulation of reactive oxygen species in leaves in a long period.In the indoor germination and liquid culture tests,PVE showed the best application effect at the concentration of 0.1?g/L.(5)Regulation mechanism of PVE on nitrogen uptake in rice seedling rootsThe application of PVE lead to the up-regulate expression of 2184 genes and down-regulate expression of 936 gene in rice seedling root.The regulated gene expressiones have a close relationship with the metabolic pathways of the construction of cell walls,oxidoreductase activity,plant hormone signal transduction,and amino acid metabolism.Real-time RCR results showed that PVE up regulated the expression of Os MRK3?Os E4.1.1.15?Os DHRS4?Os ADA?Os AGA2 and Os GGT which can improve the absorption of N.Thus,the reason for the synergistic effect of controlled release urea and PVE is that PVE promotes nitrogen metabolism in rice.