Abstract
AbstractBiochar application can influence soil nitrogen (N) cycle through biological and abiotic processes. However, studies on comprehensive examination of the effects of biochar application on microbially mediated N‐cycling processes (N mineralization, nitrification, denitrification, and fixation) and soil N fate (i.e., plant N uptake, soil N2O emission, and N leaching) are warranted. Therefore, the aim of this study was to examine the effects of biochar application on soil N transformation, microbial functional gene abundance, enzyme activity, and plant N uptake. To achieve the objective of this study, a meta‐analysis involving 131 peer‐reviewed field experiments was conducted. Results showed that field application of biochar significantly enhanced soil and content, N mineralization, nitrification, N2 fixation, and plant N uptake by 5.3%, 3.7%, 15.3%, 48.5%, 14.7%, and 18.3%, respectively, but reduced N2O emissions and N leaching by 14.9% and 10.9%, respectively. Biochar application also increased the abundance of soil denitrifying/nitrifying genes (amoA, narG, nirS/nirK+S, and nosZ), proportion of N2 fixation bacteria, and N‐acetyl‐glucosaminidase activity by 18.6%–87.6%. Soil content was positively correlated with AOA‐amoA abundance, and soil N2O emission was positively correlated with the relative abundance of genes (e.g., amoA, narG, and nirS/nirK) involved in N2O production. Furthermore, long‐term biochar application tended to increase AOB‐amoA and nirK+S abundance, especially soil N2O emission and N leaching. Overall, the findings of this study indicated that biochar application accelerated microbially mediated N‐cycling processes under field conditions, thereby enhancing soil N availability and plant productivity. However, long‐term biochar application may increase N losses. Therefore, future studies should be conducted to examine the effect of long‐term biochar application on the soil N cycle and the underlying microbial mechanisms.
Highlights
Nitrogen (N) is one of the most critical nutrients for plant growth and food production, and the use of N fertilizers has remained a key strategy in agriculture (Zamanian et al, 2018; Zhang et al, 2015)
The hypotheses formulated for validation were as follows: (1) biochar application would enhance soil N mineralization, nitrification, denitrification, and fixation by stimulating the abundance of N-relevant microbial genes and enzyme activities; (2) the enhanced microbially mediated N-cycling processes under biochar application would increase soil N availability and plant N uptake, but might result in greater soil N2O emission and N leaching; and (3) biochar load, experimental duration, climate, and soil factors could significantly alter the effects of biochar on the soil N cycle and relevant microbial properties
The present study showed that there was a significant increase in enzyme activity and the abundance of soil N-cycling genes, with the highest values obtained for soils treated with biochar load of 21–40 t ha−1 (Figure 4)
Summary
Nitrogen (N) is one of the most critical nutrients for plant growth and food production, and the use of N fertilizers has remained a key strategy in agriculture (Zamanian et al, 2018; Zhang et al, 2015). Long-term field experiments provide the opportunity to better evaluate the temporal patterns of microbially mediated N-cycling processes (N mineralization, nitrification, denitrification, and fixation) and soil N fate (i.e., plant N uptake, soil N2O emission, and N leaching) in response to biochar application. The hypotheses formulated for validation were as follows: (1) biochar application would enhance soil N mineralization, nitrification, denitrification, and fixation by stimulating the abundance of N-relevant microbial genes and enzyme activities; (2) the enhanced microbially mediated N-cycling processes under biochar application would increase soil N availability and plant N uptake, but might result in greater soil N2O emission and N leaching; and (3) biochar load, experimental duration, climate, and soil factors could significantly alter the effects of biochar on the soil N cycle and relevant microbial properties
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