Biochar promotes the growth of apple seedlings by adsorbing phloridzin

Abstract

Apple replant disease (ARD) has been reported in all major apple-growing regions of the world, and abiotic (phenolic compounds including phloridzin) and biological (bacteria, fungi and nematode) factors are important causes of ARD. This study aimed to assess the effect of phloridzin adsorption on biochar pyrolyzed at different temperatures and the effectiveness of biochar addition on the growth of Malus hupehensis Rehd. seedlings under phloridzin stress. Three biochar treatments were considered (BC300, BC400 and BC500), pyrolyzed at three different temperatures (300°C, 400°C and 500°C, respectively). Batch adsorption experiments revealed that BC300 had the maximum adsorption efficiency. The BC300 treatment was then selected for isotherm and kinetic fitting to investigate the influence of pH on the adsorption process and determine the phloridzin adsorption mechanism. The biochar was found to have a single-layer phloridzin adsorption effect, and the adsorption rate was related to the biochar concentration and pyrolysis temperature. A outdoorpot experiment was conducted to analyze the biochar adorption to phloridzin in soil. Phloridzin addition significantly inhibited seedling growth and biochar significantly reduced the soil phloridzin content. BC300 had the best adsorption effect of the three biochar treatments. Compared with the replant soil (CK), biochar (especially BC300) increased the biomass of the seedlings and the antioxidant enzyme activity in the leaves. The soil enzyme activity, organic matter and bacteria numbers increased significantly after biochar addition. The best seedling growth and soil conditions were found for BC300. These results reveal that biochar addition can significantly reduce the phloridzin content and promote seedlings growth, and the effectiveness of the biochar depends on the pyrolysis temperature.