Abstract
We examined time-dependent effect of iron oxide nanoparticles (IONPs) at a rate of 2000 mg kg−1 soil on Cynodon dactylon litter (3 g kg−1) decomposition in an arid sandy soil. Overall, heterotrophic cultivable bacterial and fungal colonies, and microbial biomass carbon were significantly decreased in litter-amended soil by the application of nanoparticles after 90 and 180 days of incubation. Time dependent effect of nanoparticles was significant for microbial biomass in litter-amended soil where nanoparticles decreased this variable from 27% after 90 days to 49% after 180 days. IONPs decreased CO2 emission by 28 and 30% from litter-amended soil after 90 and 180 days, respectively. These observations indicated that time-dependent effect was not significant on grass-litter carbon mineralization efficiency. Alternatively, nanoparticles application significantly reduced mineral nitrogen content in litter-amended soil in both time intervals. Therefore, nitrogen mineralization efficiency was decreased to 60% after 180 days compared to that after 90 days in nanoparticles grass-litter amended soil. These effects can be explained by the presence of labile Fe in microbial biomass after 180 days in nanoparticles amendment. Hence, our results suggest that toxicity of IONPs to soil functioning should consider before recommending their use in agro-ecosystems.
Highlights
Decreased the microbial activity and nutrient acquisition by fungi in soil[20,21,22]
Soil microbiota are the major drivers of litter decomposition and nutrient cycling in an agroecosystem[7,27,28,29] but only a single, very recent study reported the influence of IONPs on soil microbial community and nitrification process when applied at very low doses (0.1–10 mg kg−1 soil) in a short incubation interval of 48 hrs[17]
Treatment and time interaction for this parameter was not significant (P > 0.05). Electrical conductivity in both grass litter-amended soil (LS) and nanoparticles-grass litter amended soil (LNPS) was 42% and 49% higher, respectively compared to control soil (CS) treatment after 90 days of incubation (P = 0.000) but after 180 days this difference decreased to 38% in both treatments (Table 1)
Summary
Decreased the microbial activity and nutrient acquisition by fungi in soil[20,21,22]. The metabolic quotient, a measure of soil pollution was higher in IONPs treated compared to control soil, indicating nanoparticles stress to soil microbial activity[20]. Such nanomaterials would be accumulated or taken up by soil microbes during their life cycle[20]. Stability of IONPs is weak due to higher mobility of electron within their structure and diffusion of Fe2+ ions[26] This effect would influence its bioavailability in the soil with time and its toxicity. We hypothesized that IONPs stability will decrease with time resulting in overall decrease in their toxicity to litter carbon and nitrogen mineralization in the soil
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