Land use drives the effect of century-old biochar on taxonomic and functional diversity of springtail communities

Abstract

Although biochar is a promising climate-smart agricultural tool to stabilize carbon overtime in soils and to improve soil productivity, long-term consequences for soil organisms are barely known. Yet, it is of great importance given the role of soil fauna in ecosystem processes. The objective of the present study is to investigate the effect of century-old biochar on microbial activity and springtail communities. We used preindustrial charcoal kiln sites (CKS) in temperate soils as a model for aged biochar. Adjacent soils (REF) were used as reference. Three CKS and REF sites were selected in two contrasted textures (clay and silt-rich soils) and three land occupations (cropland, grassland, forest). Soil mesofauna samples were collected and physico-chemical and microbial properties analysed across all sites. After the springtail identification to species level, a trait-based functional approach (using FRic and RaoQ indices) was performed in complementary to taxonomic analysis. CKS soils contained larger OC, CEC, Ca2+, Mg2+ than REF with a more enhanced effect in clay-rich soils. Despite large uncertainties in microbial properties, no difference between mineralization rate of C and N between CKS and REF soils suggested little effect of aged biochar on microbial biomass and activity. The functional trait-based approach highlighted that the taxonomic shift caused by the presence of biochar led to a functional and taxonomic diversification of springtail communities in CKS in cropland, a functional and taxonomic homogenization of springtail communities in CKS in forest and a mixed effect in CKS in grassland. The present study confirmed previous findings on the effect of aged biochar on the soil physico-chemical properties. Our results demonstrated that springtail communities are strongly modified by the centennial presence of charcoal in the soil. In the case of grassland and forest silty soils, charcoal decreased the functional redundancy of springtail communities. Given that redundant species act as ‘spare wheels’ during a disturbance to maintain ecosystem functions, further research is needed to examine more in depth the long-term effect of biochar on springtail communities in other soil types.