Reduction in N2O Emissions and Improvement in Nitrifier and Denitrifier Communities through Bamboo-Biochar-Based Fertilization in Pomelo Orchard Soil

Abstract

Farmland soil is an important source of the greenhouse gas nitrous oxide (N2O), and soil nitrification and denitrification are key processes affecting N2O production. In this study, the acidic soil of a pomelo orchard was used to investigate the effects of a bamboo-biochar-based fertilizer (BB) on soil N2O emissions and nitrifier and denitrifier communities. In this study, five treatments, namely, CK (no urea and BB), N (0.72 g·kg−1 urea), 5BB+N (0.72 g·kg−1 urea plus 5 g·kg−1 BB), 10BB+N (0.72 g·kg−1 urea plus 10 g·kg−1 BB), and 20BB+N (0.72 g·kg−1 urea plus 20 g·kg−1 BB) were applied to the acidic soil of a pomelo orchard. The nitrification (AOA-amoA, AOB-amoA) and denitrification (nirS, nirK, nosZ) gene copy numbers were analyzed by qPCR, and their community diversities were determined by Illumina MiSeq sequencing. The results showed that N treatment significantly promoted soil N2O emissions compared with CK, while all BB+N treatments significantly inhibited soil N2O emissions compared with N treatment. BB fertilizer promoted soil nitrification, alleviated the adverse effects from N fertilizer inputs on the AOA-amoA gene copy numbers and community diversity, and restored the AOA-amoA diversity to the initial level. BB had a strong effect on Crenarchaeota (AOA-amoA) and Nitrosospira (AOB-amoA). BB significantly promoted the denitrification gene copy numbers; increased nirS and nirK community diversity; particularly affected the relative abundance of denitrifiers such as Nonomuraea (nirS), Proteobacteria (nirK), and Rhodanobacter (nosZ); and, finally, reduced N2O emissions.