Rashi Gupta

Effects of chemical and biological pesticides on plant growth parameters and rhizospheric bacterial community structure in Vigna radiata.

With increasing application of pesticides in agriculture, their non-target effects on soil microbial communities are critical to soil health maintenance. The present study aimed to evaluate the effects of chemical pesticides (chlorpyrifos and cypermethrin) and a biological pesticide (azadirachtin) on growth parameters and the rhizospheric bacterial community of Vigna radiata. Qualitative and quantitative analysis by PCR-denaturing gradient gel electrophoresis (DGGE) and q-PCR, respectively, of the 16S rRNA gene and transcript were performed to study the impact of these pesticides on the resident and active rhizospheric bacterial community. While plant parameters were not affected significantly by the pesticides, a shift in the bacterial community structure was observed with an adverse effect on the abundance of 16S rRNA gene and transcripts. Chlorpyrifos showed almost complete degradation toward the end of the experiment. These non-target impacts on soil ecosystems and the fact that the effects of the biopesticide mimic those of chemical pesticides raise serious concerns regarding their application in agriculture.

Nontarget effects of chemical pesticides and biological pesticide on rhizospheric microbial community structure and function in Vigna radiata

Intensive agriculture has resulted in an indiscriminate use of pesticides, which demands in-depth analysis of their impact on indigenous rhizospheric microbial community structure and function. Hence, the objective of the present work was to study the impact of two chemical pesticides (chlorpyrifos and cypermethrin) and one biological pesticide (azadirachtin) at two dosages on the microbial community structure using cultivation-dependent approach and on rhizospheric bacterial communities involved in nitrogen cycle in Vigna radiata rhizosphere through cultivation-independent technique of real-time PCR. Cultivation-dependent study highlighted the adverse effects of both chemical pesticide and biopesticide on rhizospheric bacterial and fungal communities at different plant growth stages. Also, an adverse effect on number of genes and transcripts of nifH (nitrogen fixation); amoA (nitrification); and narG, nirK, and nirS (denitrification) was observed. The results from the present study highlighted two points, firstly that nontarget effects of pesticides are significantly detrimental to soil microflora, and despite being of biological origin, azadirachtin exerted negative impact on rhizospheric microbial community of V. radiata behaving similar to chemical pesticides. Hence, such nontarget effects of chemical pesticide and biopesticide in plants’ rhizosphere, which bring out the larger picture in terms of their ecotoxicological effect, demand a proper risk assessment before application of pesticides as agricultural amendments.

Impact of chemical- and bio-pesticides on bacterial diversity in rhizosphere of Vigna radiata.

To study the effects of two chemical pesticides (chlorpyrifos and endosulfan), and a bio-pesticide (azadirachtin) on bacterial diversity in rhizospheric soil, a randomized pot experiment was conducted on mung bean (Vigna radiata) with recommended and higher doses of pesticides. Denaturing gradient gel electrophoresis was used to analyze such effects on both resident and active bacterial communities across two time points. It was observed that higher doses of azadirachtin mimicked the effects of chlorpyrifos on bacterial diversity. Both azadirachtin and chlorpyrifos showed a dose- and time-dependent effect, which was observable only at the RNA level. Endosulfan treatments showed dissimilar profiles compared to control. Most of the bands showed high sequence similarities to known bacterial groups, including many nitrogen-fixing, phosphate-solubilizing, and plant-growth-promoting bacteria. This study indicates that pesticides display non-target effects on active microbial populations that serve important ecosystem functions, thereby emphasizing the need to critically investigate and validate the use of bio-pesticides in agriculture before accepting them as safe alternatives to chemical pesticides.

Impact of Application of Biofertilizers on Soil Structure and Resident Microbial Community Structure and Function

Biofertilizers are believed to be an eco-friendly alternative to chemicals that have been used extensively in agriculture thereby contaminating the environment. The mechanism by which biofertilizers lead to positive effect on plant growth is not completely understood. Target effects of biofertilizers have been investigated before their field release to determine their efficacy. However, a largely ignored aspect in the development and release of biofertilizers has been studies on their impact on the indigenous microbial community. The introduction of biofertilizers, in numbers which largely exceed their normal populations, can change the microbial community structure and function in both positive and negative ways. It is, therefore, important to study the microbial ecology of resident microbial communities post biofertilizer application. A thorough understanding of the interactions between bioinoculants and other soil components would help in improvement of their survival and competitive ability in the rhizosphere of crops. The chapter primarily focuses in discussing the reports of impact of biofertilizers on soil structure and microbial community dynamics.

Characterization of liquid transport in needle-punched nonwovens. I. Wicking under infinite liquid reservoir

The study of wicking characteristics of fibrous materials has received significant attention from both academic and industry over many decades. Wicking describes the liquid transport behavior of fibrous assemblies, and plays a critical role in the processing and end use of nonwovens in many application areas including medical, geotextiles, filtration, etc. However, the analysis of wicking in a nonwoven materials is complex because of random arrangement of capillary tubes formed by fibers, and therefore, we must have to rely on the experimental techniques to appraise their wicking performance. In the present work, the wicking characteristics (rate and amount of liquid rise) of different nonwovens (made from polypropylene fibers) under an unlimited or infinite liquid reservoir system has been analyzed using a newly developed computerized wicking apparatus based on capacitance principle. Some factors, i.e., fiber denier, mass per unit area and needling density, were chosen for the experimental plan to find their significance on the vertical wicking. It has been found that the rate and extent of wicking is significantly affected by changing the levels of above factors (p<0.05). The rate and amount of liquid rise was increasing with increase in needling density and mass per unit area of nonwoven samples. Samples made from higher fiber denier (15 denier) were showing poor wicking results compared to lower denier samples (2.5 and 6 denier). Further work is still needed to examine other factors on the wicking to further improve our understanding of liquid transport in such highly complex porous networks.

Revisiting Action of Bioinoculants: Their Impact on Rhizospheric Microbial Community Function

Bioinoculants have been known to promote plant growth and grain yield by more than one mechanism, though it has been difficult to pinpoint them. The contribution of the impact exerted by these live microorganisms on the resident rhizospheric microbial community functioning in enhancing plant growth cannot be ruled out. The chapter aims to critically evaluate the studies that throw light on such non-target effects of bioinoculants and to bring out the existing research gaps in the area. Also, markers and methodologies, which could be good indicators of soil functioning, have been highlighted for the benefit of workers probing into similar problems.