A meta-analysis and critical evaluation of influencing factors on soil carbon priming following biochar amendment
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Previous studies have found biochar-induced effects on native soil organic carbon (NSOC) decomposition, with a range of positive, negative and no priming reported. However, many uncertainties still exist regarding which parameters drive the amplitude and the direction of the biochar priming.
Materials and methods
We conducted a quantitative analysis of 1170 groups of data from 27 incubation studies using boosted regression trees (BRTs). BRT is a machine learning method combining regression trees and a boosting algorithm, which can effectively partition independent influences of various factors on the target variable in the complex ecological processes.
Results and discussion
The BRT model explained a total of 72.4% of the variation in soil carbon (C) priming following biochar amendment, in which incubation conditions (36.5%) and biochar properties (33.7%) explained a larger proportion than soil properties (29.8%). The predictors that substantially accounted for the explained variation included incubation time (27.1%) and soil moisture (5.0%), biochar C/N ratio (6.2%), nitrogen content (5.5%), pyrolysis time during biochar production (5.1%), biochar pH (4.5%), soil C content (5.2%), sand (4.7%) and clay content (4.1%). In contrast, other incubation conditions (temperature, biochar dose, whether nutrient was added), biochar properties (biochar C, feedstock type, ash content, pyrolysis temperature, whether biochar was activated) and soil properties (nitrogen content, silt content, C/N ratio, pH, land use type) had small contribution (each < 4%). Positive priming occurred within the first 2 years of incubations, with a change to negative priming afterwards. The priming was negative for low N biochar or in high-moisture soils but positive on their reverse sides. The size of negative priming increased with rising biochar C/N ratio, pyrolysis time and soil clay content, but deceased with soil C/N ratio.
We determine the critical drivers for biochar effect on native soil organic C cycling, which can help us to better predict soil C sequestration following biochar amendment.
KeywordsBoosted regression tree Incubation time Native soil organic matter Priming effect Pyrogenic organic matter Soil respiration
We are grateful to two anonymous reviewers for their insightful advice on an earlier version of this manuscript. We thank all the researchers whose data were included in this meta-analysis. This work was supported by the National Science Foundation of China (grant numbers 41601307, 31330011, 41630755), State Key Laboratory of Forest and Soil Ecology (grant number LFSE2015-06) and the National Key Research and Development Program of China (grant number 2016YFD0200304).
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