Effect of different types of biochar on soil properties and functional microbial communities in rhizosphere and bulk soils and their relationship with CH4 and N2O emissions

Abstract

Biochar as an agricultural soil amendment plays vital roles in mediating methane (CH₄) and nitrous oxide (N₂O) emissions in soils. The link between different types of biochar, bulk soil, and rhizosphere microbial communities in relation to CH₄ and N₂O emissions is being investigated in this study. The rice pot experiment was conducted using biochar at two temperatures (300°C and 500°C) in combination with three biochar levels (0, 2, 10% w/w). Soil properties and the abundance of genes associated with CH₄ and N₂O emissions from both rhizosphere and bulk soils were investigated. The study also aimed to examine the structure of microbial communities (pmoA, nosZ) in rhizosphere and bulk soils whereas CH₄ and N₂O emissions were monitored while growing rice. Results showed that biochar at 300°C and 10% incorporation significantly increased the CH₄ emissions by up to 59% rise compared to the control group. Random Forest analysis revealed that the ratio of mcrA/pmoA along with the abundance of mcrA from both rhizosphere and bulk soils, the abundance of AOA, TN, DOC, and the community composition of pmoA-harboring microorganisms from both bulk and rhizosphere soils were important predictors of CH₄ emissions. Therefore, the ratio of mcrA/pmoA in rhizosphere soil and the abundance of AOA in bulk soil were the main factors influencing CH₄ emissions. Variation Partitioning Analysis (VPA) results indicated that the effects of these factors on bulk soil were 9% of CH₄ emissions variations in different treatments, which contributed more than rhizosphere soils' factors. Moreover, random forest analysis results indicated that the abundance of AOB in bulk soil was the most important predictor influencing N₂O emissions. The VPA result revealed that the factors in rhizosphere soil could explain more than 28% of the variations in N₂O emissions. Our study highlights that rhizosphere soil has a more significant effect than bulk soil on N₂O production. Our findings further the understanding of the link between bulk and rhizosphere attributes, and their impact on CH₄ and N₂O emissions in paddy soils. In summary, we recommend the application of biochar at 500°C and 2% incorporation rate for agricultural production in the area.

Keywords: CH4; N2O; biochar; bulk; nosZ; pmoA; rhizosphere.

Figure 1

Abundance of CH₄-related and N₂O-related functional genes in rhizosphere and bulk soils. Panels (A–I) indicate the copy numbers of functional genes in rhizosphere soils. Panels (J–R) indicate the copy numbers of functional genes in bulk soils. Error bars indicate the standard deviation of triplicate analyses. Different lowercase letters indicate significant differences in different treatments (p < 0.05). No lowercase letters indicate no significant differences among different treatments (p > 0.05). The treatment labels are as follows: CK, without biochar addition; B300, biochar pyrolyzed at 300°C; B500, biochar pyrolyzed at 500°C; M, 2% (w:w) biochar addition; H, 10% (w:w) biochar addition; R, rhizosphere soil; B, bulk soil.

Figure 2

Non-metric multidimensional scaling analysis (NMDS) (A), distribution of pmoA community composition (B), and network analysis of pmoA community in rhizosphere (C) and bulk (D) soils. The treatment labels are as follows: CK, without biochar addition; B300, biochar pyrolyzed at 300°C; B500, biochar pyrolyzed at 500°C; M, 2% (w:w) biochar addition; H, 10% (w:w) biochar addition; R, rhizosphere soil; B, bulk soil.

Figure 3

Non-metric multidimensional scaling analysis (NMDS) (A), distribution of nosZ community composition (B), and network analysis of nosZ community in rhizosphere (C) and bulk (D) soils. The treatment labels are as follows: CK, without biochar addition; B300, biochar pyrolyzed at 300°C; B500, biochar pyrolyzed at 500°C; M, 2% (w:w) biochar addition; H, 10% (w:w) biochar addition; R, rhizosphere soil; B, bulk soil.

Figure 4

The cumulative emissions of CH₄ (A) and N₂O (B) from both rhizosphere and bulk soils during the growth of rice are displayed. Error bars indicate that the standard deviation of triplicate analyses. The treatment labels are as follows: CK, without biochar addition; B300, biochar pyrolyzed at 300°C; B500, biochar pyrolyzed at 500°C; M, 2% (w:w) biochar addition; H, 10% (w:w) biochar addition. The p value (p < 0.001) is for the significant effect on the CH₄ emissions during the rice growth among different treatments. p > 0.05 indicates no significant effect on the N₂O emissions during the rice growth among different treatments.

Figure 5

The cumulative emissions of CH₄ (A) and N₂O (B), the total global warming potential (GWPt) (C) associated with N₂O and CH₄, and above-ground biomass (D) during the rice growth across different treatments are presented. Error bars indicate that the standard deviation of triplicate analyses. Different lowercase letters indicate significant differences in different treatments (p < 0.05). No lowercase letters indicate no significant differences among different treatments (p > 0.05). The treatment labels are as follows: CK, without biochar addition; B300, biochar pyrolyzed at 300°C; B500, biochar pyrolyzed at 500°C; M, 2% (w:w) biochar addition; H, 10% (w:w) biochar addition.

Figure 6

Random Forest Analysis against significant abiotic and biotic factors were analyzed for CH₄ (A) and N₂O (B) emissions. Variation Partitioning Analysis (VPA) against significant abiotic and biotic factors were analyzed for CH₄ (C) and N₂O (D) emissions. R, rhizosphere soil; B, bulk soil.