Short-term effects of biochar on soil CO2 efflux in boreal Scots pine forests

Xudan Zhu,Jukka Pumpanen,Tingting Zhu,Xuan Zhou,Yixiang Wang,Heidi Aaltonen,Frank Berninger,Liisa Kulmala,Egle Köster,Viktor J Bruckman,Naoki Makita,Marjo Palviainen,Kajar Köster

doi:10.1007/s13595-020-00960-2

Abstract

Key messageDuring the first summer, wood biochar amendments increased soil temperature, pH, and soil CO2effluxes in a xeric boreal Scots pine forest. The increase of soil CO2efflux could be largely explained by increases in by soil temperature. Higher biochar application rates (1.0 vs 0.5 kg m−2) led to higher soil CO2efflux while the pyrolysis temperature of biochar (500 or 650 °C) had no effect on soil CO2efflux.ContextUsing biochar as a soil amendment has been proposed to increase the carbon sequestration in soils. However, a more rapid soil organic matter turnover after biochar application might reduce the effectiveness of biochar applications for carbon sequestration. By raising the pyrolysis temperature, biochar with lower contents of labile carbohydrates can be produced.AimsTo better understand the effects of biochar on boreal forest soil, we applied two spruce biochar with different pyrolysis temperatures (500 °C and 650 °C) at amounts of 1.0 and 0.5 kg m−2 in a young xeric Scots pine forest in southern Finland.MethodsSoil CO2, microbial biomass, and physiochemical properties were measured to track changes after biochar application during the first summer.ResultsSoil CO2 increased 14.3% in 1.0 kg m−2 treatments and 4.6% in 0.5 kg m−2. Soil temperature and pH were obviously higher in the 1.0 kg m−2 treatments. Differences in soil CO2 among treatments disappear after correcting by soil temperature and soil moisture.ConclusionBiochar increased soil CO2 mainly by raising soil temperature in the short term. Higher biochar application rates led to higher soil CO2 effluxes. The increase in soil CO2 efflux may be transient. More studies are needed to get the optimum biochar amount for carbon sequestration in boreal forest.

Highlights

Biochar is a C-rich material produced by pyrolyzing biomass or other organic materials, such as agricultural crop residues, wood, and green waste in an oxygen-depleted environment (Ahmed and Schoenau 2015)
Palviainen et al (2018) investigated the long-term effect of biochar application on carbon and nitrogen fluxes in the same site and found that soil CO2 effluxes showed no clear response to biochar addition
Our results suggest that changes in the physical environment dominate the response of soil CO2 efflux after biochar application

Summary

Introduction

Biochar is a C-rich material produced by pyrolyzing biomass or other organic materials, such as agricultural crop residues, wood, and green waste in an oxygen-depleted environment (Ahmed and Schoenau 2015). In 2001, the term “biochar” was coined after Glaeser describing “Terra preta” soils (Glaser et al 2001). It is used as a soil amendment to increase productivity, restore soil fertility, sequester C in soil, and reduce atmospheric CO2 concentration (Woolf 2008; Van Zwieten et al 2010; Wang et al 2014). The majority of studies on the effects of biochar application on soils have been on agricultural soils (Prayogo et al 2014; Lu et al 2014; Zhang et al 2017). The effects of newly added biochar on forest ecosystems are still uncertain

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