Rahul Datta

Effect of soil sieving on respiration induced by low-molecular-weight substrates

Abstract The mesh size of sieves has a significant impact upon soil disturbance, affecting pore structure, fungal hyphae, proportion of fungi to bacteria, and organic matter fractions. The effects are dependent upon soil type and plant coverage. Sieving through a 2 mm mesh increases mineralization of exogenously supplied carbohydrates and phenolics compared to a 5 mm mesh and the effect is significant (p<0.05), especially in organic horizons, due to increased microbial metabolism and alteration of other soil properties. Finer mesh size particularly increases arabinose, mannose, galactose, ferulic and pthalic acid metabolism, whereas maltose mineralization is less affected. Sieving through a 5 mm mesh size is suggested for all type of experiments where enhanced mineralization of low-molecular-weight organic compounds needs to be minimalized.

Assessment of some cultural experimental methods to study the effects of antibiotics on microbial activities in a soil: An incubation study

Oxytetracycline (OTC) and sulfamethoxazole (SMX) are two of most widely used antibiotics in livestock and poultry industry. After consumption of antibiotics, a major portion of these compounds is excreted through the feces and urine of animals. Land application of antibiotic-treated animal wastes has caused increasing concern about their adverse effects on ecosystem health. In this regard, inconsistent results have been reported regarding the effects of antibiotics on soil microbial activities. This study was conducted based on the completely randomized design to the measure microbial biomass carbon, cumulative respiration and iron (III) reduction bioassays. Concentrations of OTC and SMX including 0, 1, 10, 25, 50, and 100 mg/kg were spiked in triplicate to a sandy loam soil and incubated for 21 days at 25°C. Results showed that the effects of OTC and SMX antibiotics on cumulative respiration and microbial biomass carbon were different. SMX antibiotic significantly affected soil microbial biomass carbon and cumulative respiration at different treatments compared to control with increasing incubation time. OTC antibiotic, on the other hand, negatively affected cumulative respiration compared to control treatment throughout the incubation period. Although OTC antibiotic positively affected microbial biomass carbon at day one of incubation, there was no clear trend in microbial biomass carbon between different treatments of this antibiotic after that time period. Nevertheless, sulfamethoxazole and oxytetracycline antibiotics had similar effects on iron (III) reduction such that they considerably affected iron (III) reduction at 1 and 10 mg/kg, and iron (III) reduction was completely inhibited at concentrations above 10 mg/kg. Hence, according to our results, microbial biomass carbon and cumulative respiration experiments are not able alone to exhibit the effect of antibiotics on soil microbial activity, but combination of these two experiments with iron (III) reduction test could well display the effects of sulfamethoxazole (SMX) and oxytetracycline (OTC) antibiotics on soil biochemical activities.

How enzymes are adsorbed on soil solid phase and factors limiting its activity: A Review

Abstract A majority of biochemical reactions are often catalysed by different types of enzymes. Adsorption of the enzyme is an imperative phenomenon, which protects it from physical or chemical degradation resulting in enzyme reserve in soil. This article summarizes some of the key results from previous studies and provides information about how enzymes are adsorbed on the surface of the soil solid phase and how different factors affect enzymatic activity in soil. Many studies have been done separately on the soil enzymatic activity and adsorption of enzymes on solid surfaces. However, only a few studies discuss enzyme adsorption on soil perspective; hence, we attempted to facilitate the process of enzyme adsorption specifically on soil surfaces. This review is remarkably unmatched, as we have thoroughly reviewed the relevant publications related to protein adsorption and enzymatic activity. Also, the article focuses on two important aspects, adsorption of enzymes and factors limiting the activity of adsorbed enzyme, together in one paper. The first part of this review comprehensively lays emphasis on different interactions between enzymes and the soil solid phase and the kinetics of enzyme adsorption. In the second part, we encircle various factors affecting the enzymatic activity of the adsorbed enzyme in soil.

Microbial expression profiles in the rhizosphere of two maize lines differing in N use efficiency

AimsStudy of the microbial expression profile in the rhizosphere of two contrasting maize lines, differing in the Nitrogen Use efficiency (NUE).MethodsThe Lo5 and T250 inbred maize characterized by high and low NUE, respectively, were grown in rhizoboxes allowing precise sampling of rhizosphere and bulk soils. We conducted metatranscriptomic of rhizosphere and bulk soil by m-RNA sequencing.ResultsHigh activity of bacteria was observed compared to archaea and fungi in both rhizosphere and bulk soils of both maize lines. Proteobacteria and Actinobacteria were involved in all processes, while significant shifts occurred in the expression of Bacteroidetes, Chloroflexi, Firmicutes, Acidobacteria, Cyanobacteria, archaea and fungi, indicating their possible role in specific processes occurring in rhizosphere of two maize lines. Maize plants with different NUE induced changes in microbial processes, especially in N cycling, with high NUE maize favouring ammonification and nitrification processes and low NUE maize inducing expression of genes encoding for denitrifying process, likely favoured by longer N residence time in the rhizosphere.ConclusionsOverall our results showed that maize lines with different NUE shaped not only microbial communities but also conditioned the microbial functions and the N cycle in their rhizosphere. While the plant NUE is genetically determined and an inherent plant physiological trait, it also stimulates changes in the microbial community composition and gene expression in the rhizosphere, favouring microbial processes that mineralize and oxidize N in the high NUE maize. These results can improve our understanding on plant-microbe interaction in the rhizosphere of crop plants with potential applications for improving the management practices of the agro-ecosystems.

Role of Soil Phosphorus on Legume Production

Legumes play a significant role in sustainable agriculture through their ability to improve soil fertility and health. Legumes, with a mutual symbiotic relationship with some bacteria in soil, can improve nitrogen (N) amount through biological N-fixation (BNF). But to maximize such functions, legumes need more phosphorus (P) as it is required for energy transformation in nodules. Besides, P also plays a significant role to root development, nutrient uptake, and growth of legume crops. But most of the agricultural soils have inadequate amounts of P to support efficient BNF as it exists in stable chemical compounds which are least available to plants. The deficiency of P causes significant yield reduction in leguminous crops. The mineral P sources are nonrenewable, unlike N. So there is a need to enhance P use efficiency (PUE) for better legume productivity and soil sustainability. Improving the PUE of applied fertilizer requires enhanced P acquisition from the soils by crops for growth and development. It is necessary to better exploit soil P resources through increasing labile soil P using leguminous crops in a rotation cycle. Moreover, incorporation of legumes in cropping system with better P management under P-deficient conditions could be a promising tool for improving legume productivity. Endowed with inherent potential PUE, deep root system, root exudate-mediated P-solubilization, and nutrient-rich residues, legumes can improve soil fertility and enhance the soil profile and efficient nutrient cycling. The data obtained from various research studies show that agriculturally important legumes can fix 40–60 million metric tons of N annually. In view of this importance of P, this chapter emphasizes on the PUE and its role in legume production for food security programs, soil sustainability, and management.

Impact of chlortetracycline and sulfapyridine antibiotics on soil enzyme activities.

Abstract Pharmaceutical antibiotics are frequently used in the livestock and poultry industries to control infectious diseases. Due to the lack of proper guidance for use, the majority of administrated antibiotics and their metabolites are excreted to the soil environment through urine and feces. In the present study, we used chlortetracycline and sulfapyridine antibiotics to screen out their effects on dehydrogenase, alkaline phosphatase and urease activity. Factorial experiments were conducted with different concentrations of antibiotic (0, 10, 25 and 100 mg kg−1 of soil) mixed with soil samples, and the enzyme activity was measured at intervals of 1, 4 and 21 days. The results show that the chlortetracycline and sulfapyridine antibiotics negatively affect the dehydrogenase activity, but the effect of sulfapyridine decreases with time of incubation. Indeed, sulfapyridine antibiotic significantly affect the alkaline phosphatase activity for the entire three-time interval, while chlortetracycline seems to inhibit its activity within 1 and 4 days of incubation. The effects of chlortetracycline and sulfapyridine antibiotics on urease activity appear similar, as they both significantly affect the urease activity on day 1 of incubation. The present study concludes that chlortetracycline and sulfapyridine antibiotics have harmful effects on soil microbes, with the extent of effects varying with the duration of incubation and the type of antibiotics used.