Interaction of TiO2 nanoparticles with soil: Effect on microbiological and chemical traits.

Titanium dioxide (TiO2) nanoparticles (NPs) are the most widely used nanomaterials and their expanding use raises concerns about their impacts on soil ecosystems and functioning. The present study evaluates the potential impacts of TiO2 NPs applied at low doses (0, 1.0, 2.5, 5.0, 10.0 and 20.0 mg L-1) on soil chemical properties including the macro and micronutrient contents, microbial population and enzyme activities in rhizosphere soil of mung bean crop at different time intervals (7, 14, 28 and 56 days). A quantitative RT-PCR study was also performed to study the relative change in the gene expression of ammonia oxidizer and nitrogen fixers upon TiO2 NP supplementation. An increase in soil nutrient content viz., available N, P, Cu, Fe, Mn, nitrate-N and ammonical-N was observed with NP application except available K and Zn content. The TiO2 NPs stimulated the growth of soil microflora at low concentrations while an inhibitory effect was recorded at high concentrations. The soil fungi and actinobacteria emerged as the most sensitive groups of soil microbes towards TiO2 NP exposure exhibiting detrimental impacts on their growth at all concentrations. Similarly, the soil enzyme activities enhanced till TiO2 NPs (10.0 mg L-1) which was followed by decrease at higher concentrations. The qRT-PCR study showed that the ammonia oxidizers were more affected by TiO2 NPs application than nitrogen fixers. These findings suggest that TiO2 NPs can be used as stimulators of soil nutrients and soil microbial dynamics at low concentrations.

Chitosan-Urea Nanocomposite for Improved Fertilizer Applications: The Effect on the Soil Enzymatic Activities and Microflora Dynamics in N Cycle of Potatoes (Solanum tuberosum L.).

The impact of polymer-based slow-release urea formulations on soil microbial N dynamics in potatoes has been sparingly deciphered. The present study investigated the effect of a biodegradable nano-polymer urea formulation on soil enzymatic activities and microflora involved in the N cycling of potato (Solanum tuberosum L.). The nano-chitosan-urea composite (NCUC) treatment significantly increased the soil dehydrogenase activity, organic carbon content and available potassium compared to the conventional urea (CU) treatment. The soil ammonical nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) contents and urease activity were significantly decreased in the NCUC-amended soil. The slow urea hydrolysis rate led to low concentrations of NH4+-N and NO3--N in the tested potato soil. Furthermore, these results corroborate the low count of ammonia oxidizer and nitrate reducer populations. Quantitative PCR (q-PCR) studies revealed that the relative abundance of eubacterial (AOB) and archaeal ammonia-oxidizing (AOA) populations was reduced in the NCUC-treated soil compared to CU. The abundance of AOA was particularly lower than AOB, probably due to the more neutral and alkaline conditions of the tested soil. Our results suggest that the biodegradable polymer urea composite had a significant effect on the microbiota associated with soil N dynamics. Therefore, the developed NCUC could be used as a slow N-release fertilizer for enhanced growth and crop yields of potato.