Elevated CO2, chlorpyrifos and biochar influence nitrification and microbial abundance in the rhizosphere of wheat cultivated in a tropical vertisol

Climate change is predicted to increase pest infestation and may lead to high use of insecticides in agriculture. Elevated CO2 and other climate factors affect soil microbial processes like nitrification. To regulate climate change biochar (BC) has been recommended for soil application. It is hypothesized that elevated CO2 and biochar may stimulate autolithotrophic nitrifiers and providing a matrix for microbial proliferation while chlorpyrifos inhibit nitrification through toxicity effect on soil microorganisms. To validate these hypotheses, Experiments were carried out to estimate nitrification in rhizosphere of wheat under the influence of elevated CO2, chlorpyrifos and biochar. The experimental factors were CO2 (400 ppm, 800 ppm), biochar (0%, 1%), and chlorpyrifos (0 ppm, 10 ppm). The parameters were nitrification rate, abundance of 16S rRNA gene of eubacteria, abundance of amoA gene, plant shoot and root biomass. Nitrification rate and microbial parameters were lowest in the treatment of CO2 400 ppm biochar 0% chlorpyrifos 10 ppm and high under CO2 800ppm biochar 1% chlorpyrifos 0 ppm. Chlorpyrifos inhibited nitrification rates by 3 folds. Similarly, the abundances of 16S rRNA gene copies of eubacteria, ammonia oxidizing bacteria were inhibited 1.36 and 2.68 times by chlorpyrifos. Plant parameters (shoot and root biomass) were highest under elevated CO2 biochar 1% and chlorpyrifos 0 ppm and lowest in CO2 400 ppm biochar 0% and chlorpyrifos 10 ppm. Principal component analysis denoted that PC1 contributed 93.28% variation and PC2 contributed 4.40% variation. Study concludes that chlorpyrifos inhibit nitrification while elevated CO2 and biochar may alleviate these negative impacts aiding in retaining soil function.