Foliar Application of Iron Nutrition Not Only Improves Root Activity but Also Significantly Affects Rhizosphere Microbial Community of Brassica Chinensis on Karst Calcareous Soil

Iron plays an important role in plant growth and development. Previous researches have indicated that application of iron nutrition is the most effective way for iron-sensitive plants growing on the iron low bioavailability soil, such as karst calcareous soil, which mainly focused on the yield, plant leaf physiology and biochemistry etc. The aim of this study was to explore the response of rhizosphere microbial community to foliar application of iron nutrition and the mechanism of increasing yield by foliar iron nutrition on B. chinensis, one kind of iron-insensitive plant. In the soil culture experiment and hydroponic experiment, the leaves of Brassica chinensis were sprayed with different concentrations of iron nutrition: 500 mg L⁻¹ (T1), 300 mg L⁻¹ (T2), 250 mg L⁻¹ (T3), 200 mg L⁻¹ (T4) of iron and deioned water (CK). After that, the aboveground biomass, SPAD, root indexes, root exudates and rhizosphere microbial community were determined. The results showed that foliar application of 200 mg L⁻¹ iron nutrition significantly improved the SPAD values and aboveground biomass of B. chinensis. In addition, 200 mg L⁻¹ of iron significantly increased root indices and promoted root metabolism in the hydroponic experiment and remarkably affected rhizosphere microbial community in the soil culture experiment. In conclusion, foliar iron nutrition could significantly enhance B. chinensis biomass by increasing chlorophyll (SPAD values), improving the root growth and activity, and changing the rhizosphere microbial community. There are remarkably correlation between the root growth and the amount of rhizosphere microorganism, but the direct relevance of root secretions and rhizosphere microorganism needs further study.