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.

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W orldwide concern about global climate change and its effects on our future environment requires a better understanding of the global carbon cycle and emissions of greenhouse gases (GHGs). The magnitude of soil CO 2 and CH 4 fluxes and their importance in the global climate system has resulted in a dramatic increase in the number of such studies in recent years. This has uncovered many new problems and opportunities, such as how to make unbiased measurements at the desired spatial and temporal scales, as well as efforts to measure more than one GHG simultaneously.Automated chamber systems have been used extensively to measure soil CO 2 efflux at many research sites around the world (e.g., Jassal et al., 2012). The non-steady-state chamber technique uses the measurement of rate of change in the chamber headspace gas mixing ratio (dc/dt) and uses a model to extrapolate it to the pre-lid-closure time (i.e., time = 0) to enable flux calculations. The chamber headspace mixing ratio does not change linearly with time due to a declining difference in mixing ratios between the soil and the chamber headspace. However, Jassal et al. (2012) showed that over short time scales of a few minutes, a linear model will cause negligible error in the calculated flux. Measurement of soil CH 4 fluxes has been generally restricted to using static chamber method, mainly due to nonavailability of robust low-cost portable CH 4 analyzers. Lai et al. (2012) and Savage et al. (2014) described simultaneous measurement of soil CO 2 and CH 4 fluxes with automated chamber systems but by using separate sensors for the two gases. In this study, we developed a method of simultaneously measuring soil CO 2 and CH 4 fluxes using a laserbased cavity ring-down spectrometer coupled to automated non-steady-state chambers. Materials and Methods Chamber System Assembly and OperationAn automatic non-steady-state chamber system was installed in a constant temperature (20°C) laboratory. The system consisted of two 0.75-m-long, 0.52-m-i.d. polyvinyl chloride cylinders and two automated chambers (Fig. 1 Agricultural & Environmental Letters Research LetterAbstract: We present a method of simultaneously measuring soil CO 2 and CH 4 fluxes using a laser-based cavity ring-down spectrometer (CRDS) coupled to an automated non-steady-state chamber system. The differential equation describing the change in the greenhouse gas (GHG) mixing ratio in the chamber headspace following lid closure is solved for the condition when a small flow rate of chamber headspace air is pulled through the CRDS by an external pump and exhausted to the atmosphere. The small flow rate allows calculation of fluxes assuming linear relationships between the GHG mixing ratios and chamber lid closure times of a few minutes. We also calibrated the chambers for effective volume (V eff ) and show that adsorption of the GHGs on the walls of the chamber caused V eff to be 7% higher than the geometric volume, with the near-surface soil porosity causing another 4% increase in V eff . Core Ideas• A me...

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