Short-term impact of biochar amendments on eukaryotic communities in three different soils

Keystone taxa of phoD-harboring bacteria mediate alkaline phosphatase activity during biochar remediation of Cd-contaminated soil

Phosphorus (P)-modified biochar can efficiently remediate cadmium (Cd)-contaminated soil. However, the mechanisms of responses of alkaline phosphatase (ALP) and phoD-harboring microorganisms, which are notably sensitive to Cd and P, are not clear during the remediation process. In this study, apple (Malus domestica) tree branches were co-pyrolyzed with tripotassium phosphate (K3PO4) to prepare P-modified biochar, which was used to remediate Cd-soil contaminated soil collected near a mine site. The effect of P-modified biochar on the composition of the phoD-harboring microbial community and its mechanism of interacting with ALP were analyzed. The results showed that the application of P-modified biochar to Cd-contaminated soil promoted the co-precipitation of Cd and phosphate and reduced the content of bioavailable Cd by 69.77 %. P-modified biochar improved the complexity and stability of the soil phoD-harboring microbial community. Furthermore, this study clarified that ALP activity was not completely regulated by the abundance of phoD, but Priestia and Massilia that contain phoD genes dominated the activity of ALP in rhizosphere and bulk soils, respectively. It is notable that bioavailable Cd significantly stimulated Priestia, Massilia, and ALP activity. These findings provide a theoretical basis for the application of P-modified biochar to the remediation of soil contaminated with Cd with respect to P functional microorganisms.

Biochar Amendment and Nitrogen Fertilizer Contribute to the Changes in Soil Properties and Microbial Communities in a Paddy Field

Biochar amendment can influence the abundance, activity, and community structure of soil microbes. However, scare information is present about the effect of the combined application of biochar with synthetic nitrogen (N) fertilizer under paddy field condition. We aimed to resolve this research gap in rice field conditions through different biochar in combination with N fertilizers on soil nutrients, soil microbial communities, and rice grain yield. The present study involves eight treatments in the form of biochar (0, 10, 20, and 30 t ha-1) and N (135 and 180 kg ha-1) fertilizer amendments. The soil microbial communities were characterized using high-throughput sequencing of 16S and Internal transcribed spacer (ITS) ribosomal RNA gene amplicons. Experiential findings showed that the treatments had biochar amendments along with N fertilizer significantly advanced soil pH, soil organic carbon (SOC), total nitrogen (TN), soil microbial carbon (SMBC), soil microbial nitrogen (SMBN), and rice grain yield in comparison to sole N application. Furthermore, in comparison with control in the first year (2019), biochar amendment mixed with N fertilizer had more desirable relative abundance of microorganism, phyla Acidobacteria, Actinobacteria, Proteobacteria, and Verrucomicrobia with better relative abundance ranging from 8.49, 4.60, 46.30, and 1.51% in T7, respectively. Similarly, during 2020, bacteria phyla Acidobacteria, Actinobacteria, Bacteroidetes, Gemmatimonadetes, Planctomycetes, and Verrucomicrobia were resulted in higher and ranging from 8.69, 5.18, 3.5, 1.9, 4.0, and 1.6%, in biochar applied treatments, respectively, as compared to control (T1). Among the treatments, Sphingopyxis and Thiobacillus bacterial genus were in higher proportion in T7 and T3, respectively, as compared to other treatments and Bacillus was higher in T6. Interestingly, biochar addition significantly decreased the soil fungi phyla Ascomycota, Basidiomycota, Chytridiomycota, and Rozellomycota, in 2020 as compared to 2019. Whereas biochar addition to soil decreased Echria, Kohlmeyeriopsis, and Westerdykella fungal genus as compared to non-biochar treatments. The redundancy analysis showed that soil biochemical traits were positively correlated with soil bacteria. In addition, correlation analysis showed that soil bacteria including Acidobacteria, Actinobacteria, Bacteroidetes, Planctomycetes, and Proteobacteria strongly correlated with rice grain yield. This study demonstrated that soil nutrients and bacteria contribute to an increase in rice yield in combined biochar amendment with lower N treatments.

Effects of biochar on soil microbial community and functional genes of a landfill cover three years after ecological restoration

Landfills, as the most common approach to disposing of municipal solid waste worldwide, disturb native ecosystems and create a need for ecological restoration. The restoration of landfill cover with biochar has shown immediate potential to improve soil microbial functions within one year. However, such characteristics could change after a longer period of time. Here, soil properties, microbial communities, and microbial functional genes related to nutrient cycling were investigated three years after the biochar amendment of the topsoil of a subtropical landfill cover. The results showed that the levels of soil organic matter, water content, total carbon (C), total nitrogen (N) and total phosphorus (P) of biochar-amended soils were higher than those of control soil. Different soil microbial community structures were observed in the biochar-amended and control soils. Nine phyla, including Proteobacteria and Acidobacteria, but not Actinobacteria or Chloroflexi, were enriched in the biochar-amended soil. Although the impact of biochar on shaping microbial communities increased after a longer period of restoration, no differences were observed in soils that were amended using different biochar:soil ratios. The abundances of functional genes related to C and N cycling decreased, whereas those of genes related to P cycling were higher in soils that received biochar amendment. This finding suggests that compared with the control soil, biochar-amended soils were less active in processes involved in C and N cycling but enhanced in processes related to P cycling. This study can serve as a reference for future ecological restoration of degraded lands using biochar.