Impact Of Different Fertilizers And Atrazine On Soil Microbial Biomass And The Gene Diversity Involved In Soil Sulfur Cycle

Soil quality was very important for sustainable management of agriculture and agricultural products.Soil microbes were another important contributor in balancing soil health.Agricultural chemicals like herbicides and fertilizers were considered as necessary evil for enhancing yield.Even though,the uses of agricultural fertilizers were significantly important to cope up with global food shortage,their impacts on ecosystem were unable to ignore.Despite from studying the adverse impacts of agricultural chemicals on human and environment they also were found strongly responsible for changing the microbial structure of the soil;which was playing a significant role in soil fertility.Soil microbial structure and their activities were reflected as a key factor of agriculture sector that not only were maintaining soil nutrients but also actively entailing in enhancing soil quality and crop productions.That why soil microorganisms were considered as bio-indicator to assess soil fertility;soil microbial activities showed a great impact on its physic-chemical properties and sustainable agricultural practices in agricultural soils were favorable for sustaining these microbial activities.Agricultural chemicals like pesticides,herbicides and fertilizers were found longer persistence in soil and they were disturbing soil health on affecting soil microbial composition.Fertilizer type was another important factor in influencing soil functioning,like bulk amount of nutrients can alter soil microbial biomass concentration,soil moisture,soil pH,enzymes and many others.All these aspects were adding in shifting the soil microbial population dynamics with straight impact of agricultural chemicals on soil profile.Although such impacts were depending on many other factors like biotic and abiotic parameters along with seasonal changes from soil quality to crop production range,still it was studied that agricultural chemicals has stronger impacts on changing soil microbial communities.These microbial communities were not only participating in maintaining soil fertility but also were regulating many other environmental activities which were significantly important in balancing life on this planet earth;like role of microorganisms in biogeochemical cycles.That's why current study was designed to observe the impact of different types of fertilizers(organic and inorganic)on soil microbial biomass and DNA concentration;Atrazine was used to study the impact of herbicides on soil microbial enrichment;especially with reference to microbes involved in soil sulfur cycle.In this study sulfar was selected for many reasons.Before this study sulfur was not point of concern to see atrazine impact but sulfur cycle was very important in soil biogeochemical cycles.Mostly sulfur was present in form of sulphates or sulphonates(carbon bonded sulfur)in agricultural lands instead of inorganic sulphates;however,plants roots were able to absorb inorganic sulphates only.So,soil microbes were found responsible to convert bonded sulphates into inorganic sulphates for plants utilization.Soil microbes were not only responsible for mineralization of bonded sulfur but also to immobilize sulphate esters present in soil.Anyhow,specified genera or species which controlled soil sulfur cycle along with sulphate reducing bacteria were yet to study further.Results concluded that type of fertilizer could alter the soil microbial biomass and DNA contents.Many other abiotic components were also found responsible for changing soil microbial concentrations but main point was the type of fertilizers.In this study soil treated with organic fertilizers resulted in higher concentrations of microbial biomass(0.0051-0.0098 g/g of soil)and DNA contents(0.53-1.49 ug/g of soil)in summers as compared to spring season where microbial biomass concentration was ranged between 0.0053-0.0085 g/g of soil and DNA concentration was ranged between 1.27-2.49ug/g of soil.Correspondingly,in soil treated with inorganic fertilizer,concentrations of soil microbial biomass(0.001-0.009 g/g of soil)and DNA(0.21-1.16 ug/g of soil)was found higher in summer season instead of spring where the soil microbial and DNA concentration was ranged between 0.002-0.005ug/g and 0.56-1.87ug/g of soil respectively.This study demonstrated the impact of fertilizers and seasonal variations on soil microbial biomass and also revealed significant correlation between soil microbial biomass and soil DNA.Soil has natural ability to recover microbes.Same trend was observed under atrazine stress.For this purpose we observed activities of soil microbial biomass and DNA under 20,50,100 and 200 mg/kg of atrazin concentrations.Results indicated that at day first soil microbial biomass and DNA concentration was ranged 0.0085g/g of soil and 1.32ug/g while on day 28 concentration of microbial biomass and DNA was 0.004g/g of soil and 0.68ug/g of soil under 20mg/kg of atrazine stress;on other hand resulted showed that higher atrazine concentrations slow down the process of microbial recovery as under 200mg/kg of atrazine stress soil microbial biomass and DNA concentration was recovered from 0.006g/g of soil to 0.002 g/g of soil and 1.32ug/g of soil to 058ug/g of soil respectively.Furthermore,total microbial count and sulphate reducing bacterial count was also investigated under atrazine stress to evaluate its impact on soil sulfur cycle.Total microbial count at day first of experiment was ranged between 26.5×104cfu/g of soil to 27×104 cfu/g of soil and highest recovery rate 22.5×104 cfu/g of soil was found under 20mgkg of atrazine stress at day 28;while lowest recovery rate of total microbial counts was observed 10.5×104 cfu/g of soil under 200mg/kg of atrazine stress at day 28.Same trend was noted in case of sulfate reducing bacteria.Highest detection of sulphate reducing bacteria(1.85×104 cfu/g of soil)was observed in microcosm treated with 20mg/kg of atrazine and lowest concentration of SRB(0.5x 104 cfu/g of soil)was shown by the microcosm treated with 200mg/kg of atrazine at day 28.Study also investigated the atrazine impact on genes involved in soil sulfur cycle aprA and dsrA under different concentrations of atrazine.No aprA and dsrA gene was detected at day 28 in treatments with higher atrazine concentrations(200mg/kg).While analyzing diversity analysis of genes involved in soil sulfur cycle under atrazine stress results demonstrated that all sequences observed in this study were much analogous to aprA genes.Maximum similarity level(99%)was found in all samples having 0 mg/kg of atrazine concentration during all experiment from day 1 to 28 while sample taken from soil containing 20mg/kg of atrazine concentration illustrated maximum similarity only at day first of testing.General tendency in similarity sequences resulted that aprA gene sequences in soil samples having highest the atrazine concentration represented the lowest matching rate while aprA gene sequence from the soil with low atrazine concentration from 0,20 and 50 mg/kg showed higher matching rate with other gene sequences in the system.Higher the atrazine concentration,higher the stress on microbial comnunity's regulation sulfur cycle and longer time required for production of soil microbes including SRBs.Results concluded that exceeding concentrations of agricultural chemicals including fertilizers and herbicides influenced the soil microbial activities.This disturbance will not only impact the soil fertility but also will cause impact on other environmental systems.