, 55 % lower compared to CF30, while no differences in nitrous oxide emissions were observed between treatments (p > 0.05). No yield differences between irrigation systems were observed in two of the rice seasons (p > 0.05) while AWDI promoted yield reduction in one of the seasons (p < 0.05). When rice yield and greenhouse gases (GHG) emissions were considered together, the AWDI irrigation system allowed for lower yield-scaled total global warming potential (GWP). Higher irrigation water productivity was achieved under AWDI in two of the three rice seasons. These findings suggest that AWDI could be an option for reducing GHG emissions and increasing irrigation water productivity. However, AWDI may compromise grain yield in certain years, reflecting the importance of the need for fine tuning of this irrigation strategy and an assessment of the overall tradeoff between relationships in order to promote its adoption by farmers.
The practice of inoculating forage legumes with rhizobia strains is widespread. It is assumed that the inoculated strain determines the performance of the symbiosis and nitrogen fixation rates. However, native-naturalized strains can be competitive, and actual nodule occupancy is often scarcely investigated. In consequence, failures in establishment, and low productivity attributed to poor performance of the inoculant may merely reflect the absence of the inoculated strain in the nodules. This study lays out a strategy followed for selecting a
Rhizobium leguminosarum
sv. trifolii strain for white clover (
Trifolium repens
) with competitive nodule occupancy. First, the competitiveness of native-naturalized rhizobia strains selected for their efficiency to fix N
2
in clover and tagged with
gus
A was evaluated in controlled conditions with different soils. Second, three of these experimental strains with superior nodule occupancy plus the currently recommended commercial inoculant, an introduced strain, were tested in the field in 2 years and at two sites. Plant establishment, herbage productivity, fixation of atmospheric N
2
(
15
N natural abundance), and nodule occupancy (ERIC-PCR genomic fingerprinting) were measured. In both years and sites, nodule occupancy of the native-naturalized experimental strains was either higher or similar to that of the commercial inoculant in both primary and secondary roots. The difference was even greater in stolon roots nodules, where nodule occupancy of the native-naturalized experimental strains was at least five times greater. The amount of N fixed per unit plant mass was consistently higher with native-naturalized experimental strains, although the proportion of N derived from atmospheric fixation was similar for all strains. Plant establishment and herbage production, as well as clover contribution in oversown native grasslands, were either similar or higher in white clover inoculated with the native-naturalized experimental strains. These results support the use of our implemented strategy for developing a competitive inoculant from native-naturalized strains.
Generation times, acid production, carbon utilization, immunological properties, plasmid content, protein profile and symbiotic properties of 15 isolates of rhizobia nodulating Lotus subbiflorus were studied. Based on specific growth rates, carbon source utilization and acid production, 13 out of the 15 isolates could be assigned to the slow-growing group of rhizobia (bradyrhizobia). Using antisera against whole cells of three isolates, we separated the 15 isolates into three serogroups. Only the slow-growing isolate Ls4 and the fast-growers Ls5 and Ls552 lacked cross-reactivity with any of the sera tested. Electrophoretic mobilities of whole cell protein from seven out of the eight isolates included in the serogroup represented by strain Ls31 were identical. Similarly, isolates Ls 1 B3 and Ls 1B4, both in serogroup Ls 1B3, had the same pattern of cell proteins. In contrast, isolates Ls3 and Ls7, belonging to serogroup Ls7, differed in protein profile. Plant growth experiments carried out under bacteriologically controlled conditions revealed that all of the isolates effectively nodulated L. subbiflorus and L. pedunculatus, but were unable to form effective nodules on L. tenuis and L. corniculatus. All isolates showed similar effectiveness in symbiosis with L. subbiflorus, except isolate Ls7, which gave significantly higher plant dry weight.Abbreviations: ELISA -enzyme linked immuno-sorbent assay, kDa -kiloDalton, MM -mineral medium, PBS -phosphate-buffered saline, RE -relative efficiency, SDS-PAGE -sodium dodecyl sulfate-polyacrylamide gel electrophoresis, YEM -yeast extract mannitol.
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