Effects of carbonized graphene on yield, soil nutrient of rhizosphere and microbial community structure of Capsicum annuum L.

【Objective】To explore the effects of carbonized graphene on yield，quality and rhizosphere soil nutrient，enzyme activity，heavy metal content and microbial community structure of Capsicum annuum，so as to provide a scientific basis for the application of graphene carbon-fertilizer in the cultivation of pepper with high yield，high efficiency and good quality.【Method】The fresh type of pepper was taken as the research object，based on of basic fertilization（CK）， 0.07% graphene aqueous solution（A8 treatment），0.35% graphene aqueous solution（B8 treatment）and 1.75% graphene aqueous solution（C8 treatment）were sprayed on the rhizosphere of C. annuum after planting. C. annuum fruit yield，nutritional indicators，heavy metal content in different organs of treated with different concentrations of graphene，as well as soil nutrients，enzyme activity and heavy metal content in the rhizosphere of C. annuum were measured. Soil microbial community structure of C. annuum treated with different concentrations of graphene was analyzed.【Result】Different concentrations of graphene treatment had certain effects on the yield and quality of C. annuum. The yield，vitamin C content and capsaicin content of B8 treatment were significantly increased by 6.40%，25.27% and 20.45% respectively compared with CK（P<0.05，the same below）. There was no significant change in protein content（P>0.05，the same below），soluble sugar content decreased significantly，while nitrate content increased significantly. There was no significant difference in the contents of total phosphorus，total nitrogen，total potassium and soil hydrolytic nitrogen in the rhizosphere of C. annuum among the treatments，but the contents of available phosphorus and available potassium of CK were higher or significantly higher than those of graphene treatments. The organic matter content of B8 treatment was slightly higher than that of CK，and that of A8 treatment was slightly lower than that of CK. Graphene treatment could significantly increase the activity of soil acid protease，reduce the activity of catalase，and have a certain impact on the activities of sucrase， urease，acid phosphatase and nitrate reductase. In the middle growth stage of C. annuum，the contents of lead and chromium in the rhizosphere soil of the three graphene treatments were lower than that of CK，and the contents of cadmium and arsenic were higher than that of CK. There was little difference in mercury content between different treatments. In the fruit of C. annuum，the contents of cadmium and chromium in the three graphene treatments were lower than that of CK， among which the contents of cadmium in A8，B8 and C8 treatments were 18.52%，22.22% and 19.75% lower than that of CK，and the contents of chromium were 14.02%，39.25% and 42.99% lower than that of CK，respectively. The sequencing results of soil microorganisms in the rhizosphere of C. annuum treated with different concentrations of graphene showed that the total number of soil microbial OTU treated with CK，A8，B8 and C8 were 2016，2074，2182 and 2063 respectively. The same OTU number in four samples was 1106，and the number of unique OTU was 218，224，445 and 221 respectively. The analysis results of soil microbial composition of each treatment showed that the dominant bacterial groups in the soil were Proteobacteria，Firmicutes，Bacteroidota，Acidobacterita，Chloroflexi and Actinobacterita，which were common groups in farmland soil.【Conclusion】Spraying 0.35% graphene aqueous solution after planting can improve soil fertility and enzyme activity in the rhizosphere of pepper to a certain extent，improve soil physical and chemical properties and microbial community structure，and improve the yield and quality of C. annuum. Graphene has the potential to be used as carbon fertilizer in pepper cultivation with high yield，high efficiency and high quality.