Biochar influences on soil CO2 and CH4 fluxes in response to wetting and drying cycles for a forest soil

Mark S Johnson,Rachhpal S Jassal,Cameron Webster,T Andrew Black,Iain Hawthorne

doi:10.1038/s41598-017-07224-6

Abstract

Biochar has been the focus of significant research efforts in agriculture, but little research has been conducted in forested ecosystems. Here, we assess CO2 and CH4 fluxes from a forest soil in response to biochar additions using a before-after-control-intervention experimental design. Soil CO2 and CH4 fluxes were measured over a series of wetting cycles by coupling soil mesocosms equipped with auto-chambers to a laser-based spectrometer for high-frequency measurements of gas fluxes and related soil processes. We found that soil CO2 fluxes were higher and CH4 fluxes were less negative (e.g. reduced CH4 uptake) for the biochar-amended soil compared to the no biochar condition. Furthermore, biochar improved soil infiltrability under wet conditions, and enhanced soil moisture levels under dry conditions. Biochar additions shifted the point of maximum soil respiration (i.e. soil CO2 efflux) to a slightly wetter soil moisture level. The point of maximum CH4 uptake was also shifted to a slightly wetter moisture level for soil with biochar. Overall differences in soil gas fluxes were found to be minor compared to the increase in soil carbon resulting from the biochar addition. Biochar may thus contribute to improved forest management through increases to soil carbon stocks and improved soil moisture levels.

Highlights

Almost 200,000 ha of forest are harvested and replanted in British Columbia each year, which has a significant impact on the soil carbon (C) stocks of managed forest landscapes
The experiment was structured to simulate rainfall patterns typical of coastal British Columbia with wetting cycles occurring in rapid succession for the wet season, and drying phases interrupted by occasional wetting for the dry season
Little is known regarding gas fluxes from forest soils in response to biochar additions. These fluxes are of interest as they help to determine the climatic effect of C management in forested ecosystems, where biochar additions can enhance soil C stocks[24] and improve forest biomass production[7]

Summary

Introduction

Almost 200,000 ha of forest are harvested and replanted in British Columbia each year, which has a significant impact on the soil carbon (C) stocks of managed forest landscapes. Carbon sequestration is a key priority for British Columbia, where a forest carbon offset protocol is already in place[4], burning forest harvest slash material to facilitate replanting and reduce fire risk remains a common practice for managed forest landscapes in the province, releasing ~8 Mt CO2 yr−1 into the atmosphere[5]. We designed a controlled experiment to evaluate the impact of biochar additions to a forest soil from a managed forest in coastal British Columbia on soil gas fluxes of carbon dioxide (CO2) and methane (CH4). We hypothesized that biochar additions would affect soil CO2 and CH4 fluxes by influencing soil moisture content

Methods

Results

Conclusion