Thermal treatment and leaching biochar alleviates plant growth inhibition from mobile organic compounds
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Abstract
Recent meta-analyses of plant responses to biochar boast positive average effects of between 10 and 40 %. Plant responses, however, vary greatly across systems, and null or negative biochar effects are increasingly reported. The mechanisms responsible for such responses remain unclear. In a glasshouse experiment we tested the effects of three forestry residue wood biochars, applied at five dosages (0, 5, 10, 20, 50 t/ha) to a temperate forest drystic cambisol as direct surface applications and as complete soil mixes on the herbaceous pioneers Lolium multiflorum and Trifolium repens. Null and negative effects of biochar on growth were found in most cases. One potential cause for null and negative plant responses to biochar is plant exposure to mobile compounds produced during pyrolysis that leach or evolve following additions of biochars to soil. In a second glasshouse experiment we examined the effects of simple leaching and heating techniques to ameliorate potentially phytotoxic effects of volatile and leachable compounds released from biochar. We used Solid Phase Microextraction (SPME) – gas chromatography – mass spectrometry (GC-MS) to qualitatively describe organic compounds in both biochar (through headspace extraction), and in the water leachates (through direct injection). Convection heating and water leaching of biochar prior to application alleviated growth inhibition. Additionally, growth was inhibited when filtrate from water-leached biochar was applied following germination. SPME-GC-MS detected primarily short-chained carboxylic acids and phenolics in both the leachates and solid chars, with relatively high concentrations of several known phytotoxic compounds including acetic acid, butyric acid, bisphenol and benzonoic acid. We speculate that variable plant responses to phytotoxic organic compounds leached from biochars may largely explain negative plant growth responses and also account for strongly species-specific patterns plant responses to biochar amendments in short-term experiments.
Cite this as
2016. Thermal treatment and leaching biochar alleviates plant growth inhibition from mobile organic compounds. PeerJ Preprints 4:e2123v1 https://doi.org/10.7287/peerj.preprints.2123v1note This preprint is not peer-reviewed. You may wish to reference the subsequent peer-reviewed version of this article.
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This is a submission to PeerJ for review.
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Supplemental Information
Contrast coefficients for ryegrass growth responses to biochar
Supplementary Table S1. Simultaneous confidence intervals and test statistics for multiple comparisons (contrasts) of performance traits for ryegrass in experiment 1. Significant differences are in boldface type (p < 0.05)
Contrast coefficients for clover growth responses to biochar
Supplementary Table S2. Simultaneous confidence intervals and test statistics for multiple comparisons (contrasts) of performance traits for clover in experiment 1. Significant differences are in boldface type (p < 0.05)
Contrast coefficients for ryegrass growth to treated biochars
Supplementary Table S3. Simultaneous confidence intervals and test statistics for multiple comparisons (contrasts) of performance traits for ryegrass in experiment 2. Significant differences are in boldface type (p < 0.05)
Dose-response script for Experiment.1
source code for linear regression analyses performed in experiment 1: biomass and leaf area response effect sizes as a function of increasing biochar dosage.
Data set for lolium in experiment 1
Data set containing lolium growth responses in experiment 1
dataset of clover growth responses to biochars in experiment 1
raw-data of clover growth responses to biochars in experiment 1
Ryegrass growth responses to treated biochars and leachates
raw data of ryegrass growth responses to treated biochars and leachates
data set for dose-response analyses in experiment 1
clover performance traits in experiment 1 presented as response ratios
Data set for dose-response analyses in experiment 1
ryegrass performance traits in experiment 1 presented as response ratios
Additional Information
Competing Interests
The authors declare that they have no competing interests
Author Contributions
Nigel V Gale conceived and designed the experiments, performed the experiments, analyzed the data, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.
Tara E Sackett conceived and designed the experiments, performed the experiments, wrote the paper, reviewed drafts of the paper.
Sean C Thomas conceived and designed the experiments, contributed reagents/materials/analysis tools, wrote the paper, reviewed drafts of the paper.
Data Deposition
The following information was supplied regarding data availability:
The raw data has been supplied as a supplemental dataset.
Funding
Funding was provided by the Natural Sciences and Engineering Research Council of Canada. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
