Search results for "N fixation"

Quantification of denitrifying bacteria in soils by nirK gene targeted real-time PCR.

2004

Abstract Denitrification, the reduction of nitrate to nitrous oxide or dinitrogen, is the major biological mechanism by which fixed nitrogen returns to the atmosphere from soil and water. Microorganisms capable of denitrification are widely distributed in the environment but little is known about their abundance since quantification is performed using fastidious and time-consuming MPN-based approaches. We used real-time PCR to quantify the denitrifying nitrite reductase gene (nirK), a key enzyme of the denitrifying pathway catalyzing the reduction of soluble nitrogen oxide to gaseous form. The real-time PCR assay was linear over 7 orders of magnitude and sensitive down to 102 copies by assa…

Isolation and Characterization of High-Efficiency Rhizobia From Western Kenya Nodulating With Common Bean.

2021

Common bean is one of the primary protein sources in third-world countries. They form nodules with nitrogen-fixing rhizobia, which have to be adapted to the local soils. Commercial rhizobial strains such as Rhizobium tropici CIAT899 are often used in agriculture. However, this strain failed to significantly increase the common bean yield in many places, including Kenya, due to the local soils’ low pH. We isolated two indigenous rhizobial strains from the nodules of common bean from two fields in Western Kenya that have never been exposed to commercial inocula. We then determined their ability to fix nitrogen in common beans, solubilize phosphorus, and produce indole acetic acid. In greenhou…

Biological nitrogen fixation of some landraces of sulla (Hedysarum coronarium) in Mediterranean environment

2004

Morpho-agronomic and genetic diversity among twelve sicilian agro-ecotypes of lentil (Lens culinaris)

2015

Although Sicily is relatively small (about 25000 km2), it accounts for several agro-ecotypes of lentil (Lens culinaris Medik.), for many of which no data on morphological, agronomic, and organoleptic characteristics are available to date. Thus, experiments were performed to characterize 12 lentil agro-ecotypes from different areas of Sicily, including some small islands surrounding the main island, and to assess the extent of genetic diversity (by means of six inter-simple sequence repeat [ISSR] primers). A famous agro-ecotype from central Italy (Castelluccio di Norcia) and two commercial varieties from Canada (Eston and Laird) were also included in the study. The results showed a large deg…

Nitrogen fixation and methanotrophy in forest mosses along a N deposition gradient

2013

Abstract Nitrogen deposition has decreased the plant-associated nitrogen (N 2 ) fixation when measured using the indirect acetylene reduction assay (ARA). However, nitrogen deposition can also lead to changes in the diversity of moss symbionts, e.g. affect methanotrophic N 2 fixation, which is not measured by ARA. To test this hypothesis we compared ARA with the direct stable isotope method ( 15 N 2 incorporation) and studied methanotrophy in two mosses, Hylocomium splendens and Pleurozium schreberi , collected from seven forest sites along a boreal latitudinal N deposition transect. We recognized that the two independent N 2 fixation measures gave corresponding results with the conversion …

Methanotrophy induces nitrogen fixation during peatland development

2013

Significance In peatlands, the external sources of nitrogen are mainly atmospheric, but the atmospheric nitrogen deposition alone cannot explain the long-term annual nitrogen accumulation rates to these ecosystems. Because of methodological problems, methane-induced fixation of atmospheric dinitrogen gas has been previously overlooked as an additional nitrogen input mechanism. We found that the activity of methane-oxidizing bacteria provides not only carbon but also nitrogen to peat mosses and, thus, contributes to carbon and nitrogen accumulation in peatlands, which store approximately one-third of the global soil carbon pool. Our results imply that nitrogen fixation in wetlands may be str…

Invasional meltdown via horizontal gene transfer of a European symbiosis island variant in North American nodule symbionts of Cytisus scoparius

2022

New data from sites in Spain, Sicily and North America establish that the spread of the European legume Cytisus scoparius (Scotch broom) across North America involved the concurrent invasion of a European mobile genetic element (symbiosis island [SI]) into North American Bradyrhizobium nodule bacteria. At four SI loci, bacteria from nine C. scoparius populations across the continent were all identical to haplotypes present in European Bradyrhizobium strains. At seven non-symbiotic (housekeeping) loci, these American C. scoparius bacteria grouped into eight diverse lineages related to, or in some cases identical to, symbionts from several native North American legumes. Inoculation experiment…

Effects of indole-3-acetic acid on Sinorhizobium meliloti survival and on symbiotic nitrogen fixation and stem dry weight production

2009

We evaluated the effects of the main auxin phytohormone, indole-3-acetic acid (IAA), on the central metabolism of Sinorhizobium meliloti strain 1021. We either treated the Sinorhizobium meliloti 1021 strain with 0.5 mM IAA (1021+) or use a derivative, RD64, of the same strain harbouring a pathway for IAA biosynthesis converting tryptophan into IAA via indoleacetamide. We assayed the activity of key enzymes in the major energy-yielding pathways (Entner-Doudoroff, Embden-Meyerhof-Parnas, pentose phosphate, glyoxylate bypass and tricarboxylic acid cycle). We found that activity of two main regulative tricarboxylic acid (TCA) cycle enzymes was increased. Citrate synthase (CS) activity, as compa…

Influence of arbuscular mycorrhizae on biomass production and nitrogen fixation of berseem clover plants subjected to water stress.

2014

Several studies, performed mainly in pots, have shown that arbuscular mycorrhizal symbiosis can mitigate the negative effects of water stress on plant growth. No information is available about the effects of arbuscular mycorrhizal symbiosis on berseem clover growth and nitrogen (N) fixation under conditions of water shortage. A field experiment was conducted in a hilly area of inner Sicily, Italy, to determine whether symbiosis with AM fungi can mitigate the detrimental effects of drought stress (which in the Mediterranean often occurs during the late period of the growing season) on forage yield and symbiotic N2 fixation of berseem clover. Soil was either left under water stress (i.e., rai…

Symbiotic N2 fixation activity in relation to C economy of Pisum sativum L. as a function of plant phenology

2003

The relationships between symbiotic nitrogen fixation (SNF) activity and C fluxes were investigated in pea plants (Pisum sativum L. cv. Baccara) using simultaneous 13 C and 15 N labelling. Analysis of the dynamics of labelled CO 2 efflux from the nodulated roots allowed the different components associated with SNF activity to be calculated, together with root and nodule synthetic and maintenance processes. The carbon costs for the synthesis of roots and nodules were similar and decreased with time. Carbon lost by turnover, associated with maintenance processes, decreased with time for nodules while it increased in the roots. Nodule turnover remained higher than root turnover until flowering…