Biochar-induced Soil Priming Effects And Associated Mechanisms

Biochar,which is more biologically and chemically recalcitrant than its feedstocks,is commonly considered to be beneficial for soil carbon sequestration and climate change following the addition to soil.However,it was reported that biochar would intensively stimulate humus mineralization thus offset its potential of carbon sequestration.Impact of biochar amendment on soil organic mineralization has become a frontier research area.Acceleration(positive priming effects)and depression(negative priming effects)of soil organic carbon(SOC)mineralization induced by biochar were both widely reported,and no robust conclusion has been reached.Biochar characterization and soil types are major explanation of various priming effects.Natural abundance of 13C was used in this research to distinguish carbon source(biochar and SOC)in soil respiration.Incubation experiments,consisted of a typical red soil with 12 kinds of biochar and 8 soil amended with single biochar,were conducted to investigate priming effects differentiation and microbial community response.We made the following conclusion in this study:(1)We used grass\com\cane\peanut shell as feedstock,slow pyrolysed at 300\400\500℃ under limited oxygen condition,yielded 12 types of biochar.Feedstcoks had major impact on biochar properties,influence of temperature was largely depended on feedstock types during slow pyrolysis at low and medium temperature.Cellulose and lignin content in feedstocks were closely related to C content,C/O,C/N,DOC and ash.High cellulose feedstock yielded biochar was more susceptible of temperature alternation.(2)Biochar induced positive priming effects in the selected red soil,except Peanut-B300.The magnitude of negative priming effects were-0.14 g C kg-1 dry soil mass,accounted for-0.47%of soil organic matter.Grass-B induced the largest positive priming effects,which is 1.21g C kg-1 dry soil mass.Impact of pyrolysis temperature on biochar-induced priming effects largely relied on its feedstock types,cellulose and lignin content in feedstock were associated with priming effect magnitude.Feedstock with different proportion of cellulose and lignin tended to interact with soil organic matter in different ways.The early stage of priming effects(first 8 days)was due to microbial uptaken of labile carbon and other nutrients from biochar,thus accelerat the microbial organisms turnover.Consistent with previous research,Actinobacteria(G+)and Firmicutes(G+)dominated at this stage.In fungi community,Sordariomycetes and Tremellomycetes were responsible for the longer period of real priming effects after day 40 of incubation.(3)Soil pH,organic matter and native microbial community diversity of soil,probably related to biochar induced negative priming effect magnitude.Following biochar addition,soil with more acidity,lower organic carbon content and simpler microbial community composition,intended to stimulate more intensive negative priming effects.Substrate like biochar(considered to be biologically or chemically inert),the degradability was not only determined by its chemical properties,also largely relied on soil types or the interaction between soil and substrate.Biochar addition tended to depress fungal community diversity,and the suppression on bacterial community only occurred in soils with low organic carbon content and pH,which indicated that impact of biochar on microbial community depended on soil organic carbon and pH.