The positive effects of biochar application on Rhizophagus irregularis, rice seedlings, and phosphorus cycling in paddy soil

Phosphorus (P) is an essential element for plant growth but is often limiting in ecosystems; therefore, improving the P fertilizer use efficiency is important. Biochar and arbuscular mycorrhizal fungi (AMF) may enhance P cycling in paddy soils that contain high total P but low available phosphorus (AP). In this study, the effects of biochar and Rhizophagus irregularis inoculation on the organic and inorganic P contents and phosphatase activity of paddy soil, rice seedling growth, and AMF colonization ability were investigated. Compared with the control, biochar enhanced the percentage spore germination at day 7, hyphal length, most probable number, and mycorrhizal colonization rate of R. irregularis by, on average, 32%, 662%, 70%, and 28%, respectively. Biochar and R. irregularis altered soil P cycling and transformed soil P availability. Biochar and R. irregularis, either individually or in combination, increased the soil AP content by 2%–48%. Rice seedlings treated with biochar and R. irregularis produced greater biomass, and showed improved root morphology and higher nutrient uptake compared with those of the control. The results suggest that combined application of biochar and R. irregularis is beneficial for rice cultivation in paddy soils with high total P but low AP content.