A survey of the ecological variability within 52 populations of Schoenoplectus californicus (C.A. Mey.) Soják across its distributional range revealed that it is commonly found in nitrogen (N) limited areas, but rarely in phosphorus limited soils. We explored the hypothesis that S. californicus supplements its nitrogen demand by bacterial N2-fixation processes associated with its roots and rhizomes. We estimated N2-fixation of diazotrophs associated with plant rhizomes and roots from several locations throughout the species' range and conducted an experiment growing plants in zero, low, and high N additions. Nitrogenase activity in rhizomes and roots was measured using the acetylene reduction assay. The presence of diazotrophs was verified by the detection of the nifH gene. Nitrogenase activity was restricted to rhizomes and roots and it was two orders of magnitude higher in the latter plant organs (81 and 2032 nmol C2H4 g DW-1 d-1, respectively). Correspondingly, 40x more nifH gene copies were found on roots compared to rhizomes. The proportion of the nifH gene copies in total bacterial DNA was positively correlated with the nitrogenase activity. In the experiment, the contribution of fixed N to the plant N content ranged from 13.8% to 32.5% among clones from different locations. These are relatively high values for a non-cultivated plant and justify future research on the link between N-fixing bacteria and S. californicus production.
- MeSH
- bakteriální proteiny metabolismus MeSH
- distribuce rostlin MeSH
- druhová specificita MeSH
- dusík chemie metabolismus MeSH
- fixace dusíku * MeSH
- fosfor chemie metabolismus MeSH
- kořeny rostlin metabolismus MeSH
- mokřady * MeSH
- nitrogenasa metabolismus MeSH
- oddenek metabolismus mikrobiologie MeSH
- oxidoreduktasy metabolismus MeSH
- půda chemie MeSH
- rostlinné proteiny metabolismus MeSH
- šáchorovité metabolismus mikrobiologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- Jižní Amerika MeSH
- Severní Amerika MeSH
In situ nitrogen fixation was investigated in a cyanobacterial mat growing on the bed of rocks of the Muga River, Spain. The filamentous non-heterocystous cyanobacterium Schizothrix dominated the mat, showing nitrogenase activity in the light at similar rates to those found in nearby heterocystous Rivularia colonies. N2 fixation in the light was significantly increased by an inhibitor of PSII and oxygen evolution, DCMU (3-[3,4-dichlorophenyl]-1,1-dimethylurea), and anaerobic conditions. However, no nitrogenase activity was found in the dark. Addition of fructose as a respiratory substrate induced nitrogenase activity in samples incubated under aerobic conditions in the dark but not in anaerobic conditions. Microelectrode oxygen profiles showed internal microaerobic microzones where nitrogen fixation might concentrate. Analyses of the 16S rRNA gene revealed only the presence of sequences belonging to filamentous non-heterocystous cyanobacteria. nifH gene diversity showed that the major phylotypes also belonged to this group. One of the three strains isolated from the Schizothrix mat was capable of fixing N2 and growing in the absence of combined N. This was consistent with the nifH gene analysis. These results suggest a relevant contribution of non-heterocystous cyanobacteria to nitrogen fixation in these mats.
The effect of UV-C radiation on thylakoid arrangement, chlorophyll-a and carotenoid content and nitrogenase activity of the cyanobacterium Microchaete sp. was studied. Chlorophyll-a and carotenoid content increased gradually up to 48 h of UV-C exposure but declined with longer exposures. Nitrogenase activity decreased moderately with 6 to 12 h exposure and decreased substantially afterwards. When cells exposed to UV-C for 12 to 24 h, grown under fluorescent light for 144 h, nitrogenase activity increased to levels greater than in the control cells. The exposure of UV-C treated cells to fluorescent light, however, did not result in recovery of pigment content. In Microchaete sp. cells treated with UV-C for 144 h, thylakoid membranes became dense, were aggregated into bundles, and were surrounded by spaces devoid of cytoplasm.
The well-developed biological soil crusts cover up to 40% of the soil surface in the alpine and subnival zones of the Tibetan Plateau, accounting for a vast area of Asia. We investigated the diversity and biomass of the phototrophic part (Cyanobacteria) of the microbial community inhabiting biological soil crusts and uncrusted soils in their surroundings on the elevation gradient of 5200-5900 m a.s.l. The influence of soil physico-chemical properties on phototrophs was studied. The ability of high-altitude phototrophs to fix molecular nitrogen was also determined under laboratory conditions. The biological soil crust phototroph community did not differ from that living in uncrusted soil in terms of the species composition, but the biomass is three-to-five times higher. An increasing trend in the cyanobacterial biomass from the biological soil crusts with elevation was observed, with the genera Nostoc spp., Microcoleus vaginatus and Phormidium spp. contributing to this increase. Based on the laboratory experiments, the highest nitrogenase activity was recorded in the middle elevations, and the rate of nitrogen fixation was not correlated with the cyanobacterial biomass.
- MeSH
- biodiverzita MeSH
- biomasa MeSH
- dusík metabolismus MeSH
- ekosystém * MeSH
- fixace dusíku MeSH
- nadmořská výška MeSH
- nitrogenasa metabolismus MeSH
- půda chemie MeSH
- půdní mikrobiologie * MeSH
- sinice klasifikace enzymologie fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
The potential for N(2) fixation by heterocystous cyanobacteria isolated from soils of different geographical areas was determined as nitrogenase activity (NA) using the acetylene reduction assay. Morphology of cyanobacteria had the largest influence on NA determined under light conditions. NA was generally higher in species lacking thick slime sheaths. The highest value (1446 nmol/h C(2)H(4) per g fresh biomass) was found in the strain of branched cyanobacterium Hassalia (A Has1) from the polar region. A quadratic relationship between NA and biomass was detected in the Tolypothrix group under light conditions. The decline of NA in dark relative to light conditions ranged from 37 to 100 % and differed among strains from distinct geographical areas. Unlike the NA of temperate and tropical strains, whose decline in dark relative to light was 24 and 17 %, respectively, the NA of polar strains declined to 1 % in the dark. This difference was explained by adaptation to different light conditions in temperate, tropical, and polar habitats. NA was not related to the frequency of heterocysts in strains of the colony-forming cyanobacterium Nostoc. Colony morphology and life cycle are therefore more important for NA then heterocyst frequency. NA values probably reflect the environmental conditions where the cyanobacterium was isolated and the physiological and morphological state of the strain.
