Phosphorus-Laden Biochar Mitigates Soil Aluminum Toxicity and Promotes Pakchoi (Brassica chinensis) Growth in Acidic Conditions

The potential impacts of nutrient-rich biochar as a soil amendment have attracted increasing attention. However, their effects on the alleviation of aluminum toxicity are unclear. A pot experiment was carried out to assess the impact of phosphorus (P) laden biochar on the morphological, physiological, and chemical indicators of plants and bacteria community structure in acidic soil. The experiment had five treatments: CK (control), P (100 mg P fertilizer kg-1 soil), B (2% biochar), P + B (2% biochar plus 100 mg P kg-1 soil), and PLB (2% phosphorus-laden biochar) with three replicates. P-laden biochar changed soil pH, and significantly decreased exchangeable aluminum (Al3+), through adsorption and complexation processes. At the same time, the PLB treatment significantly increased bacteria related to the P cycle, such as (Proteobacteria (26.06%), Actinobacteria (32.4%), Bacteroidetes (10.8%), and Firmicutes (13.5%), thus increasing phosphorus availability in soil. All biochar treatments, particularly PLB treatment, enhanced the photosynthetic parameters and plant growth of pakchoi. PLB treatment increased the antioxidative capacity and total soluble sugar, while it decreased the content of malondialdehyde (MDA) in the leaf compared to biochar treatment. Moreover, principal component analysis (PCA) provided a clear picture of the impact of Al and P contents in acid soil on plant responses under all treatments. Our findings show a positive effect of PLB application in acidic soil, which may provide new strategies for reducing the bioavailability of Al in soil and alterations in bacteria-related P cycle, thus enhancing P uptake of plants.