Biochar alters soil properties, microbial community diversity, and enzyme activities, while decreasing conifer performance

Biochars are porous charcoal-like materials that can enhance soil health and plant growth, but its use has not been adequately evaluated in woody cropping systems. We set up an experimental Christmas tree plantation on a Marlette series soil amended with two types of biochar and conducted two studies on the impacts of biochar on the agroecosystem over three years following establishment. The first study investigated the effects of biochar on plant performance, soil physicochemical properties and extracellular enzyme activities, while the second investigated the response of the root-associated fungal community. Both biochars stimulated five extracellular enzyme activities, with increases of between 67% and 446%. Structural equation modelling identified increases to dissolved organic carbon and soil moisture as potential mechanisms of biochar’s effects on enzyme activities. Tree growth and survival were negatively affected by biochar application, depending on the tree species and biochar applied, which may have been due to induced nitrogen limitation. High-throughput sequencing showed that biochar decreased the diversity of root-associated fungal communities, with the ectomycorrhizal species Wilcoxina mikolae reaching levels of hyper-dominance on balsam fir in response to one of the biochars. Further studies should investigate how biochar can be harnessed to remediate specific soil quality issues or restructure soil ecosystems in ways that improve crop performance. ### Competing Interest Statement The authors have declared no competing interest. * EEA : extracellular enzyme activity ECM : ectomycorrhizal TDN : total dissolved nitrogen DOC : dissolved organic carbon PRS : plant root simulator BG : β-glucosidase CBH : cellobiohydrolase LAP : leucine aminopeptidase NAG : β-N-acetyl glucosaminidase PER : peroxidase PHEN : phenoloxidase PHOS : acid phosphatase EDX : energy dispersive X-ray spectroscopy ITS : internal transcribed spacer PCR : polymerase chain reaction ANOVA : analysis of variance PERMANOVA : permutational multiple analysis of variance ANCOM : analysis of composition of microbiomes OTU : operational taxonomic unit