Studies on salinization in Haryana soils on free‐living nitrogen‐fixing bacterial populations and their activity

Abstract

A total of 26 soil samples from saline soils of Haryana were collected. Based on their electrical conductivity (EC) values, which varied from 1.04 to 21.00 dS m(-1), the soils were categorized into non-saline soils (EC 0-2 dS m(-1)), weakly saline soils (EC 2-4 dS m(-1)), saline soils (EC 4-8 dS m(-1)), strongly saline soils (EC 8-16 dS m(-1)), and very strongly saline soils (EC >16 dS m(-1)). The pH values of these soil samples ranged from 6.03 to 8.62, while organic C, total N, and available P were in the range of 0.06-0.94%, 0.07-0.15%, and 0.11-0.29 μg g(-1) soil, respectively. As a measure of the impact of salinity on free-living N(2) fixers and their activity, the total bacterial populations on four media (Jensen's nitrogen-free medium, malate medium, Burk's medium, and soil extract agar medium) decreased from 6.12 to 3.70 log CFU g(-1) soil with increasing salinity level. PCR amplification of the nifH region of the DNA from 234 selected morphotypes from all the media showed the presence of nifH in 71 isolates. Out of these, 37% of the isolates were obtained using Jensen's medium; 35, 28, and 21% of the isolates were obtained using soil extract medium, Burk's medium, and malate medium, respectively. The majority of the free-living N(2) fixers (67%) were Gram negative. Apart from the acetylene reduction assay (ARA) activity in these isolates, other beneficial traits like ammonia excretion and indole acetic acid (IAA) production were also present. A decreasing trend in the activities was observed with increasing salinity levels. Isolates JN6, BP8, and MJ4 showed the highest ARA activity, ammonia excretion, and IAA production. The performance of isolates like BNC2 with good ARA activity, ammonia excretion, and IAA production and isolated from a very strongly saline soil should be further evaluated under high-saline conditions.

The Root Microbiome of Salicornia ramosissima as a Seedbank for Plant-Growth Promoting Halotolerant Bacteria

“…N-fixation was overall less frequent than either P-solubilization or siderophore production and was not represented in one of the subsets of isolates (Al). Nitrogen fixation is energetically costly for bacteria [30] and negatively affected by soil salinity [89,90], which can explain the low number of isolates exhibiting this feature. In Salicornia-dominated areas, cyanobacteria have a very important role in Nitrogen fixation, especially in warmer months and low plant density areas [91].…”

“…The low organic matter content of Al sediments may explain a poorer spectrum of bacterial extracellular enzymatic activities but not the lack of N-fixing isolates in the Al subset. The abundance of diazotrophs in sediments tends to decrease with increasing salinity [89,90], but Al sediments would be the least stressful in terms of salinity and conductivity. Therefore, their highly saline pore waters (Table 1) or other factors (e.g., moisture, total N, C/N ratio) not covered by the set of physico-chemical parameters may be involved [97,98].…”

Bioaugmentation of soil with Enterobacter cloacae AKS7 enhances soil nitrogen content and boosts soil microbial functional-diversity

“…A 0.1 mL aliquot was collected from appropriate dilution and aseptically spread onto Burk's medium supplemented with agar (Merck). Burk's medium has been found to be used in previous reports to isolate nitrogen-fixing bacteria from soil (Park et al 2005;Kayasth et al 2014;Chakraborty and Tribedi 2019). The composition of Burk's medium was as follows-…”

Response of some characteristics of selected beneficial soil microorganisms under different potassium fertilizer applications

“…The CFU counts were performed after 5 days of incubation. The specific media used were as follows: i) Jensen's Agar Medium (HiMedia™) for the population of nitrogen-fixing bacteria according to the method of Kayasth et al (2014), ii) Yeast Mannitol Agar medium (HiMedia™) for the population of Rhizobium species, iii) Pikovskaya's Agar medium (Pikovskaya, 1948) for the population of phosphate-solubilizing soil microorganisms, iv) King's Medium B Base (HiMedia™) for the population of Pseudomonas sp., and v) Aleksandrow medium (HiMedia™) for the population of potassium-solubilizing bacteria. In order to determine the microbial activity of the treated soils under study, the basal respiration activity was estimated using NaOH entrapment of CO 2 evolved due to microbial respiration according to the modified method of Alef (1991).…”