Application Study Of Enhanced Phosphorus Uptake In Drought-stressed Maize With Hydroxyapatite-bentonite Nano-composites

Nanohydroxyapatite(HAP)is a new type of nano-phosphorus fertilizer that has small particle size,large surface area,strong adsorption capacity,and good stability,making it an effective phosphorus source for plants.To enhance its solubility in alkaline soil,nanobentonite(BE)was used to prepare functionalized nanocomposites with different ratios of BE to HAP through hydrothermal synthesis.Soil incubation experiments were conducted to investigate the variation of available phosphorus content in sandy soil.Additionally,maize pot experiments were conducted to explore the effects of functional nanocomposites on maize growth and phosphorus uptake under drought stress.The impact of nanocomposites on the root-associated soil bacterial microbial community was studied using high-throughput sequencing.The main findings are as follows:1.Functional nanocomposites with different ratios of BE to HAP(1:1 BE-HAP,5:1 BEHAP,10:1 BE-HAP)were successfully synthesized through hydrothermal synthesis.The synthesized nanocomposites exhibited reduced charge and particle size,increased surface area,and improved adsorption performance,as confirmed by various characterization techniques.2.The soil incubation experiment revealed that the BE-HAP treatment significantly increased the available phosphorus content by 64.8%,42.3%,21.3%,and 84.2% on days 1,28,42,and 56,respectively.The 5:1 BE-HAP and 10:1 BE-HAP treatments showed significant increases of 83.1% and 81.5% on day 1,respectively.However,they exhibited significant decreases on days 28 and 42,with reductions of 33.4%,142.4%,16.7%,and 39.6%,respectively.On day 56,both treatments showed increases of 74.2% and 26.3%,respectively.The enhancement of available phosphorus content in sandy soil by nanocomposite treatment gradually weakened with an increase in the BE ratio.3.The maize pot experiment demonstrated that the 1:1 BE-HAP treatment significantly improved maize growth and biomass under drought stress,enhancing photosynthesis and antioxidant capacity.It reduced the content of malondialdehyde and accumulation of reactive oxygen species in plant tissues,while increasing the activity of antioxidant enzymes.The 1:1BE-HAP treatment also exhibited significant effects in increasing soil available phosphorus content,total phosphorus content,phosphorus content in maize plants,and alkaline phosphatase activity.However,there were no significant differences between the 5:1 BE-HAP and 10:1 BE-HAP treatments and the control group.4.For the Beta diversity of bacterial community,different nano-composites all changed the structure of bacterial community,and the 10:1 BE-HAP treatment was the most significant.In terms of species composition,the relative abundance of Planctomycetota,Chloroflexi and Marinobacter was significantly improved under 10BE-HAP treatment.FAPROTAX functional prediction results showed that both 5:1 and 10:1 BE-HAP promoted several processes related to the carbon and nitrogen cycles,such as nitrogen fixation,nitrate denitrification,nitrate ammoxidation,methanol oxidation and chitinolysis.Spearman correlation analysis showed that the relative abundance of bacteria(Planctomycetota and Zeaxanthinibacter)increased under 10BE-HAP treatment was positively correlated with total phosphorus,available phosphorus and alkaline phosphatase.In conclusion,the three nanocomposites significantly increased the soil available P content under drought stress,and the available P content decreased gradually with the growth of culture time,indicating that the BE-HAP composite has a good slow release effect.At the same time,the combined application of hydroxyapatite and bentonite can improve the solubility of phosphorus and reduce the fixation of phosphorus in soil,so as to increase the absorption of phosphorus nutrients by maize.In addition,the microbial community analysis showed that the characteristic microorganisms related to the carbon and nitrogen cycle were significantly enriched under different proportions of composite materials,which indirectly promoted the dissolution and transformation of phosphorus in soil.This study demonstrated the application potential of hydroxyapatite-bentonite nanocomposite as a new phosphorus fertilizer,and provided certain theoretical basis and technical support for improving the utilization rate of phosphorus fertilizer,reducing phosphorus fixation and promoting the absorption and utilization of phosphorus by crops in arid regions in the future.