Abstract
Autotrophic nitrification is regulated by canonical ammonia-oxidizing archaea (AOA) and bacteria (AOB) and nitrite-oxidizing bacteria (NOB). To date, most studies have focused on the role of canonical ammonia oxidizers in nitrification while neglecting the NOB. In order to understand the impacts of combined biochar and chemical fertilizer addition on nitrification and associated nitrifiers in plant rhizosphere soil, we collected rhizosphere soil from a maize field under four different treatments: no fertilization (CK), biochar (B), chemical nitrogen (N) + phosphorus (P) + potassium (K) fertilizers (NPK), and biochar + NPK fertilizers (B + NPK). The potential nitrification rate (PNR), community abundances, and structures of AOA, AOB, complete ammonia-oxidizing bacteria (Comammox Nitrospira clade A), and Nitrobacter- and Nitrospira-like NOB were measured. Biochar and/or NPK additions increased soil pH and nutrient contents in rhizosphere soil. B, NPK, and B + NPK treatments significantly stimulated PNR and abundances of AOB, Comammox, and Nitrobacter- and Nitrospira-like NOB, with the highest values observed in the B + NPK treatment. Pearson correlation and random forest analyses predicted more importance of AOB, Comammox Nitrospira clade A, and Nitrobacter- and Nitrospira-like NOB abundances over AOA on PNR. Biochar and/or NPK additions strongly altered whole nitrifying community structures. Redundancy analysis (RDA) showed that nitrifying community structures were significantly affected by pH and nutrient contents. This research shows that combined application of biochar and NPK fertilizer has a positive effect on improving soil nitrification by affecting communities of AOB and NOB in rhizosphere soil. These new revelations, especially as they related to understudied NOB, can be used to increase efficiency of agricultural land and resource management.
Highlights
To meet the food needs of a large population, excess chemicals are often applied in agricultural production (Liu et al, 2015)
Compared with CK, biochar and/or NPK amendment obviously increased the contents of soil organic matter (OM), available phosphorus (AP), total phosphorus (TP), total nitrogen (TN), and NO3− in rhizosphere soil, with the highest values in the B and B + NPK treatments
Addition of biochar alone significantly stimulated soil potential nitrification rate (PNR) compared to the CK treatment, indicating that biochar addition had a positive effect on PNR, which was in line with a recent study that manure-based biochar increased the gross nitrification rate in rhizosphere soil using the 15N isotope labeling technique (Pokharel et al, 2021)
Summary
To meet the food needs of a large population, excess chemicals are often applied in agricultural production (Liu et al, 2015). The overuse and low use efficiency of chemical fertilizers have led to serious environmental problems such as soil acidification (Guo et al, 2010), increased greenhouse gas emissions (Hu et al, 2015), and surface water and groundwater pollution (Sebilo et al, 2013). This pathway is closely correlated with environmental problem and food production, which has attracted extensive attention in the past several decades (Koops et al, 2006). Nitrite oxidation can become the limiting step for nitrification in disturbed soil ecosystems, and NOB has immense ecological significance as a principal source of NO3− that supports primary biological production on Earth (Galloway et al, 2008)
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