Biochar Influences Greenhouse Gas Fluxes In Forest Humus Layer In Xing ’an Type Permafrost Region

The Daxing’an Mountains region is distributed with a large area of permafrost,which is extremely sensitive to climate change.The forest humus soil in the permafrost regions of the Daxing’an Mountains contains rich carbon resources,and greenhouse gas（GHG）emissions under freezing and thawing have an important impact on global warming.Global warming brings about increased temperatures and an increase in the thickness of the active layer of permafrost,which increase the risk of decomposition of forest soil organic matter and GHG emissions in permafrost regions.Biochar has a stable structure,large specific surface area,and well-developed pore structure.Biochar has a strong adsorption effect,promotes the formation of soil aggregates,changes soil permeability,and can improve soil carbon storage under certain conditions.Currently,biochar is widely used as a soil conditioner.However,the effects of biochar on soil organic matter decomposition and GHG emissions in forest permafrost are unclear and need further research.The humic soil of three forest types（Larix gmelinii forest,Betula platyphylla forest,L.gmelinii and B.platyphylla mixed forest）was collected in the Xing’an type permafrost region,and laboratory experiments were conducted to investigate the effects of no freeze-thawing and freeze-thawing on permafrost under different biochar additions respectively.The objective is to reveal the impact of freeze-thawing and biochar conditions on GHG emissions from forest permafrost.The main conclusions include the following:（1）Experimental studies on forest permafrost with different biochar additions shows that biochar can improve the stability of total organic carbon（TOC）in soil and significantly increase the content of TOC and ammonia nitrogen.For the three forest types in the permafrost area of Xing’an,TOC content increased with the increase of biochar addition.Under the condition of 8%biochar addition,the soil TOC content of Larix gmelinii forest,Betula platyphylla forest and mixed forest increased by 21.2%,15.5%and 16.6%,respectively.Dissolved organic carbon（DOC）content of soil decreased with the increase of biochar addition,and biochar effectively alleviated the mineralization of soil organic matter.Under the condition of 8%biochar addition,the addition of biochar can significantly increase the soil electrical conductivity（EC）,and the soil EC of the three forest types increased by 633%,260%and 733%,respectively.（2）The study of GHG flux changes in forest permafrost soils under different biochar addition conditions shows that biochar has a high adsorption capacity,improves the stability of soil organic matter,and inhibits soil CO₂ emissions.Because Betula platyphylla forest soil has the highest organic matter content,the inhibitory effect of biochar on CO₂ emissions is more obvious and increases with the increase of biochar addition.During the cooling process at 25℃,the CO₂ emissions from the soil of the Betula platyphylla forest with 8%biochar decreased by 34.4%.Biochar can inhibit the absorption of CH₄ in soil,and the inhibition effect is proportional to the amount of biochar added.The addition of biochar can inhibit the warming potential of global warming and play a leading role in inhibiting CO₂ emissions.In the cooling process,biochar has a greater inhibitory effect on the warming potential of global warming than in the warming process.（3）The effects of biochar on GHG emissions from permafrost under freeze-thawing cycles shows that freeze-thawing inhibited CO₂ emissions and CH₄ absorption in three forest types of soil.Freeze-thawing are beneficial to improving the pore structure of biochar,which improves the adsorption of CO₂ by biochar.The impact analysis of biochar and freeze-thaw on GHG emissions from Xing’an type permafrost regions shows that under freeze-thaw conditions,biochar can inhibit GHG emissions from forest soils and reduce global warming potential.Adding biochar to the Xing’an permafrost region is a potential method to reduce GHG emissions.The research results have important scientific value for reducing GHG emissions from forest soils in the permafrost region.