Arbuscular Mycorrhizae Affect Soil Nitrogen Fertilizer Utilization, Denitrification Functional Genes, and N₂O Emissions During Biochar Amendment

Abstract

Arbuscular mycorrhizal fungi (AMF) can form symbionts with plant roots, acquire soil nitrogen, and affect nitrous oxide (N2O) production. Biochar, as a soil additive for the management of agricultural soil, affects soil nitrogen (N) utilization and plant growth. However, how AMF regulates soil N unitization, the denitrification process, and N2O emissions in plant–soil systems remains largely unknown, particularly under the biochar amendment. In this study, a microcosm experiment was conducted to investigate the impacts of different mycorrhizal treatments (CK: neither AMF hyphae nor plant roots; AMF: only AMF hyphae; AMF + R: AMF hyphae and plant roots) on plant growth, soil N fertilizer utilization, N2O production and consumption, functional gene abundance, and N2O emission at two biochar addition levels (B0: no biochar; B1: biochar addition rate of 10 g·kg−1 soil) in a maize planting soil system. The results revealed that AMF alone and AMF with plant root treatments enhanced the fresh weight of maize plants by 10.15% and 19.23% and decreased soil inorganic N contents by 33.28% and 75.56%, respectively. The combination of biochar, AMF, and plant roots showed the largest increase in maize plant biomass. The AMF and AMF with root treatments all significantly decreased the nirS + nirK/nosZ ratio and N2O emissions at two biochar levels. The presence of AMF and plant roots during biochar amendment showed the smallest nirS + nirK/nosZ ratio and N2O emissions. The AMF combined with biochar and AMF and plant roots combined with biochar treatments increased nirS + nirK/nosZ by 24.32% and 26.90% and decreased N2O accumulation emission by 21.12% and 38.13%, respectively. The results imply that biochar, AMF, and plant roots reduced N2O emissions directly by reducing soil N and increasing soil N unitization efficiency and indirectly by shifting the N2O production and consumption gene abundance in agroecosystems. These findings suggest that the addition of biochar and AMF and/or the presence of plant roots can interact to alleviate soil N2O emissions by manipulating plant inorganic N acquisition and the soil denitrification process.

Keywords

• arbuscular mycorrhizal fungi
• denitrification
• plant biomass
• nitrogen uptake
• nitrogen retention