Biochar‐Modulated Microbial Communities Improve Phosphorus Cycling and Rice P Uptake in Low‐P Paddy Soil

ABSTRACT Phosphorus (P) is a key macronutrient for plants. Nevertheless, its low efficiency and overuse in paddy soil were addressing important agricultural and environmental issues. Biochar has been generally accepted as an effective and environmentally friendly material for improving soil fertility, but its role in soil P cycling and related microbial processes has not been adequately understood. In this study, a field microcosm experiment was carried out to assess the impact of three biochar types (rice husk biochar, BC; low‐phosphorus biochar, LP; high‐phosphorus biochar, HP) at two rates (0.5% and 2%, w: w) on soil P fractions, arbuscular mycorrhizal (AM) fungal colonization, microbial community structure, and rice growth. Biochar addition significantly increased soil pH, total carbon content, and total nitrogen content, and also significantly affected soil P fractions by increasing P availability. HP addition significantly increased soil total P, available P, and phosphatase activity by 3%, 158%, and 76%, respectively. Compared with all other treatments, the 0.5% HP treatment significantly increased rice shoot dry weight by 11% and 40% P accumulation in shoot and 29% in root, together with a higher AM fungal colonization rate. In contrast, grain yield was not significantly different among treatments, indicating that biochar addition mainly improved soil fertility and nutrient uptake ability rather than grain yield under the experimental conditions. Metagenomic analysis further showed that HP addition increased microbial richness and diversity and changed microbial community structure by reducing the relative abundance of Acidobacteria and Chloroflexi, increasing genes involved in fructose metabolism, and increasing the abundance of AM fungi and beneficial bacteria. In general, these findings showed that biochar, especially 0.5% HP, improved soil P cycling and microbial functional potential, and thus improved paddy soil P cycling and rice P uptake. This study emphasizes the importance of targeted biochar application as a sustainable approach for optimizing P management in paddy soils.