A.K. Kashyap

Methane flux from irrigated rice fields in relation to crop growth and N-fertilization

Abstract The effects of N-fertilization on rice plant growth (number of tillers, shoot and root biomass, root volume and porosity, grain yield) and their relationship with methane flux was investigated in three irrigated varieties of Oryza sativa L. (Sarju-52, Malviya-36 and Pant Dhan-4). The study design consisted of (a) control (unfertilized) vegetated, (b) fertilized vegetated, (c) control (unfertilized) bare, and (d) fertilized bare plots; laid down in a completely randomized block design in triplicate. Urea was applied in (b) and (d) in three split doses at a rate of 40, 30 and 30 kg N ha−1 at the time of transplanting, active tillering and grain filling stages of crop. The field was submerged before transplanting and the water depth ranged from 6.7 to 23.9 cm in response to rainfall. Every 10 d, crop growth and CH4 flux were measured from d 9 to 115 after rice transplanting. Sarju-52 and Pant Dhan-4 were similar in phenological stages but different than Malviya-36. Results showed that there were significant differences in all the growth variables measured for all the rice varieties due to growth period and fertilization. Variety×treatment, variety×growth period and treatment×growth period interactions were significant for all growth variables. Maximum CH4 flux from control (vegetated) plots was observed at the flowering stage (65 d after transplanting in Sarju-52 and Pant Dhan-4 and 76 d after transplanting in Malviya-36) and ranged from 10.79 to 14.20 mg m−2 h−1. In vegetated fertilized plots, maximum CH4 emission was observed 10 d later than in the vegetated control plots and ranged from 14.43 to 20.20 mg m−2 h−1. These values were from 7- to 12.3-fold higher than bare (unfertilized) plots. All growth variables, except mean shoot and root biomass, showed strong positive relationships with seasonal CH4 emission. It was concluded that the CH4 source strength was dependent on the rice variety under cultivation, its phenology, growth variables and soil fertilization.

Cyanobacteria in alkaline soil and the effect of cyanobacteria inoculation with pyrite amendments on their reclamation

The succession of cyanobacteria was studied in a usar (alfisol, solonetz, alkaline) soil, located in a tropical region of upper Gangetic plain, following the first rainfall for a period of 10 months (i.e., July–April). A dozen cyanobacteria were identified to grow on the soil surface and their appearance was in the following order: Microcoleus sp., Calothrix brevissima, Scytonema sp., Cylindrosprmum licheniformae, Cylindrosprmum fertilissima, Nostoc calcicola, Nostoc punctiformae, Aphanothece parietina, Nostoc commune, Aulosira fertilissima, Phormidium sp., and Oscillatoria sp. Among these cyanobacteria, N. calcicola was the dominant species. N. calcicola was inoculated on the alkaline soil and incubated under ambient conditions in the light for 2 years in the laboratory. Changes in soil properties were more rapid after the incorporation of pyrite (FeS2). Recovery was monitored by using a filamentous heterocystous cyanobacterium N. calcicola and its bicarbonate-resistant (HCO3−R) mutant. The mutant strain showed better response to modification of soil pH following growth in soil.

Microbial biomass C, N and P in disturbed dry tropical forest soils, India.

Abstract Variations in microbial biomass C (MB-C), N (MB-N) and P (MB-P) along a gradient of different dominant vegetation covers (natural forest, mixed deciduous forest, disturbed savanna and grassland ecosystems) in dry tropical soils of Vindhyan Plateau, India were studied from January 2005 to December 2005. The water holding capacity, organic C, total N, total P and soil moisture content were comparatively higher in forest soils than in the savanna and grassland sites. Across different study sites the mean annual MB-C, MB-N and MB-P at 0–15 cm soil depth varied from 312.05 ± 4.22 to 653.40 ± 3.17, 32.16 ± 6.25 to 75.66 ± 7.21 and 18.94 ± 2.94 to 30.83 ± 23.08 μg g −1 dry soil, respectively. At all the investigated sites, the maximum MB-C, MB-N and MB-P occurred during the dry period (summer season) and the minimum in wet period (rainy season). In the present study, soil MB-C, MB-N and MB-P were higher at the forest sites compared to savanna and grassland sites. The differences in MB-C, MB-N and MB-P were significant ( P P P P P P P mixed deciduous forest > savanna > grassland. The results suggested that deforestation and land use practices (conversion of forest into savanna and grassland) caused the alterations in soil properties, which as a consequence, led to reduction in soil nutrients and MB-C, MB-N and MB-P in the soil of disturbed sites (grassland and savanna) compared to undisturbed forest ecosystems.

Factors Affecting Formation of Spores (Akinetes) in Cyanobacterium Anabaena doliolum (AdS strain)

Summary The effect of various physical and chemical factors on spore formation of Anabaena doliolum [AdS strain*)] was investigated under laboratory conditions. Among the three inorganic nitrogen sources, nitrate and nitrite (0.5 mM) were slightly stimulatory to sporulation, however, the specific growth rate was reduced in comparison to N-free grown culture. Ammonium (all concentrations) was inhibitory to growth as well as to sporulation. Dilution of phosphate in the medium was stimulatory whereas dilution of the medium was inhibitory to sporulation. Temporal relationship between spore differentiation, depletion of phosphate from the medium, and development of alkaline phosphatase activity suggest that induction of this enzyme may be considered as one of the important events preceeding sporulation. Metabolic inhibitors like sodium azide, sodium fluoride, and sodium arsenate were stimulatory either in terms of the time required for sporulation or the spore frequency. Growth rate as well as sporulation of A. doliolum was more enhanced at 32 ±2 °C than at 25 ±1 °C. Increasing light intensities (from 500lx to 3,000lx) increased the sporulation frequency with a gradual decrease in the time required for spore initiation. pH 8.0 of the medium was most suitable for sporulation.

Genetic control of ammonium transport in nitrogen fixing cyanobacterium Nostoc muscorum

SummaryAmmonium (NH4+) transport was investigated in Nostoc muscorum ISU (wild type) and spontaneous mutants resistant to cyanophage N-1 (Nm/N-1), streptomycin (Nm/Sm) and methylamine (Nm/MA). N2-fixing wild-type cells transported NH4+via two transport systems: the ‘high-affinity’ (Km 11 μM) and ‘low-affinity’ (Km 66 μM), which formed 10 and 50-fold concentration gradients, respectively. The high-affinity system of Nm/MA (Km 11 μM) was similar to the wild type but the low-affinity system had reduced affinity for NH4+(Km 125 μM), while Nm/N-1 and Nm/Sm mutants had only a high-affinity transport system (Km 20 and 28 μM, respectively). The growth of mutant Nm/N-1 was more sensitive to 1 mM NH4+or methylamine than other strains, and also glutamine-synthetase activity was most reduced in NH4+-grown cells. l-methionine-d, l-sulfoximine (20 μM) treatment of N2-grown Nm/N-1 cells resulted in a higher rate of NH4+efflux. The apparent alterations in kinetic constants of NH4+transport in mutants and glutamine synthetase activity suggested that NH4+in N. muscorum is transported by specific carrier(s) and the transport is genetically controlled.

Nitrogenase activity of the antarctic cyanobacteriumNostoc commune: Influence of temperature

Nitrogenase activity (C2H2 reduction) ofNostoc commune isolated from Schirmacher Oasis (Antarctica) was compared withNostoc muscorum, N. calcicola, Anabaena doliolum andGloeocapsa sp. The temperature profile of acetylene reduction (5–30 °C) forN. commune revealed (a) that the highest rate of nitrogenase activity was at 25±1 °C, (b) that it was low (69 %) in comparison withN. muscorum, and (c) that nitrogenase activity continued at lower temperatures, which was not evident for other cyanobacteria. The results suggest thatN. commune is adapted to lower temperatures in terms of nitrogen fixation.

Nutrient status, algal and cyanobacterial flora of six fresh water streams of Schirmacher Oasis, Antarctica

The algal and cyanobacterial flora and the chemical environment of six freshwater streams of Schirmacher Oasis, Antarctica were investigated. Over 30 species of algae, predominantly cyanobacteria (Cyanophyceae), were recorded. N2-fixing species, both heterocystous and unicellular diazotrophs, contributed more than 50% to the counts and their dominance was greatest in the middle of the stream where nitrogen and other nutrients were low. Green algae and diatoms also contributed to the flora. The species composition varied between streams. Glacial and snow drift meltwater streams contained a distinctive community. Based on diversity indices, these streams could be classified into two clusters.

Hydrogen photoproduction by filamentous non-heterocystous cyanobacterium Plectonema boryanum and simultaneous release of ammonia

Abstract Plectonema boryanum (filamentous, non-heterocystous cyanobacterium) photoproduced H 2 when cells grown aerobically in nitrate were transferred to microaerobic or anaerobic conditions without nitrate. It was observed that H 2 photoproducing cells simultaneously excreted ammonium in the medium, which was possibly due to phycocyanin degradation [decrease in chlorophyll a (Chl a ):phycocyanin ratio in comparison to aerobic nitrate-grown cells]. Although nitrogenase (measured as H 2 evolution) was induced in Ar:CO 2 (96:4 v/v), inclusion of N 2 in the gas phase (Ar:CO 2 :N 2 , 72:4:24 v/v) resulted in a 2-fold increase in H 2 evolution. Addition of l -methionine DL-sulphoximine (MSX, glutamine-synthetase inhibitor), besides stimulating ammonium excretion in the medium, resulted in a 4.5-fold increment of H 2 photoproduction (1.43 μmol H 2 mg −1 dry wt h −1 ) in comparison to cells in Ar:CO 2 gas phase (0.31 μmol H 2 mg −1 dry wt h −1 ). Inhibition of photosystem II by 3(3,4-dichlorophenyl)1,1-dimethyl urea (DCMU) caused an increment of 1.6 and 3.2-fold in Ar:CO 2 and Ar:CO 2 :N 2 , respectively, in comparison to cells incubated in Ar:CO 2 gas phase alone. Simultaneous production of H 2 and NH 4 + was at a maximum when MSX and DCMU were added together in suboptical concentrations. Immobilization of cells in calcium alginate prolonged the duration (12 days) of H 2 evolution and NH 4 − excretion.

Enhanced hydrogen photoproduction by non-heterocystous cyanobacterium Plectonema boryanum

Abstract Nitrogenase activity was derepressed in Plectonema boryanum following 18–24 h of microaerobic incubation. The cyanobacterium evolved hydrogen at a slow rate. Addition of reducing substances (sulfide, sulfite or dithionite) to the diazotrophic cultures resulted in an increase in nitrogenase activity or photoproduction of hydrogen. The reducing substances also restored phycocyanin degradation.

Evaluating the potential of N. calcicola and its bicarbonate resistant mutant as bioameleorating agents for ‘usar’ soil

The potential of Nostoc calcicola and its bicarbonate resistant mutant as bioameleorating agent was investigated, using laboratory simulation experiments, in terms of their growth potential, glutamine synthetase (GS) activity, heterocyst frequency and effect on pH of soil. Nostoc calcicola, exhibited a tendency to lower the pH of ‘usar’ soil significantly and showed better growth and pigment content at 20% soil extract as compared to basal medium. The bicarbonate resistant mutant (HCO3−R) exhibited a better ability to grow at higher percentage of soil extract (60%), besides bringing about a more significant change in soil pH as compared to wild type. The heterocyst frequency was much higher in the mutant strain, which was not significantly affected by growth in various concentrations of soil extract. The mutant strain holds promise as a potential bioameliorant for ‘usar’ soil after further evaluation of its reclamative properties at field level.