Effects of root-applied biochar on soil nitrogen transformation and root nitrogen metabolism of cucumber seedlings in facility continuous cropping soils
The problem of soil barrier caused by excessive accumulation of nitrogen is common in continuous crop-ping soil of facility agriculture.To investigate the modulating effects of biochar amendment on soil nitrogen transfor-mation in greenhouse continuous cropping systems,we conducted a pot experiment with two treatments,no biochar addition(CK)and 5％biochar addition(mass ratio).We analyzed the effects of biochar addition on soil microbial community structure,abundances of genes functioning in nitrogen cycling,root growth and nitrogen metabolism-re-lated genes expressions of cucumber seedlings.The results showed that biochar addition significantly increased plant height,root dry mass,total root length,root surface area,and root volume of cucumber seedlings.Rhizosphere en-vironment was improved,which enhanced root nitrogen absorption by inducing the up-regulation of genes expres-sions related to plant nitrogen metabolism.Biochar addition significantly increased soil microbial biomass nitrogen,nitrate nitrogen,and nitrite nitrogen contents.The abundances of bacteria that involved in nitrogen metabolism,in-cluding Proteobacteria,Cyanobacteria,and Rhizobiales(soil nitrogen-fixing bacteria),were also significantly im-proved in the soil.The abundances of genes functioning in soil nitrification and nitrogen assimilation reduction,and the activities of enzymes involved in nitrogen metabolisms such as hydroxylamine dehydrogenase,nitronate monoox-ygenase,carbonic anhydrase were increased.In summary,biochar addition improved soil physicochemical proper-ties and microbial community,and affected soil nitrogen cycling through promoting nitrification and nitrogen assimi-lation.Finally,nitrogen adsorption capacity and growth of cucumber plant was increased.
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