The susceptibility of soil microbial metabolism and diazotroph functional groups to silica nanoparticles

The agro-ecological effect of silica nanoparticles on soil metabolism has been investigated by microcalorimetry with specific enzymatic tests (urease, catalase and fluorescein diacetate hydrolase, FDA) and diazothroph account. Three SNP doses (10, 25 and 50 mg kg-1) corresponding to each dimension (9, 12 and 40 nm) were used. The thermodynamic parameters obtained from the power-time curves showed an increase, with some exception, of total heat output, microbial growth rate constant (k) and heat output peak (Pmax) by increasing SNP dose, indicating a general stimulation of microbial populations. Urease and FDA activity, except catalase, showed similar positive size-dose response thus supporting microcalorimetric analysis. However, no direct effects on diazotrophs were found. The results confirmed the capability of SNP to maintain or enhance nitrogenous nutrient availability and to promote microbial deoxygenation of the soil microenvironments. SNP did not depress total microbial biomass (no changes in FDA) or impair plant nutrition and the diazotroph taxa.