Nitrogen Fixation Dynamics of Two Diazotrophic Communities in Mono Lake, California

Abstract

Two types of diazotrophic microbial communities were found in the littoral zone of alkaline hypersaline Mono Lake, California. One consisted of anaerobic bacteria inhabiting the flocculent surface layers of sediments. Nitrogen fixation (acetylene reduction) by flocculent surface layers occurred under anaerobic conditions, was not stimulated by light or by additions of organic substrates, and was inhibited by 2, nitrate, and ammonia. The second community consisted of a ball-shaped association of a ifiamentous chlorophyte (Ctenocladus circinnatus) with diazotrophic, nonheterocystous cyanobacteria, as well as anaerobic bacteria (Ctenocladus balls). Nitrogen fixation by Ctenocladus balls was usually, but not always, stimulated by light. Rates of anaerobic dark fixation equaled those in the light under air. Fixation in the light was stimulated by 3-(3,4-dichlorophenyl)-1,1-dimethylurea and by propanil [N-(3,4-dichlorophenyl)propanamide]. 3-(3,4-Dichlorophenyl)-1,1-dimethyl urea-elicited nitrogenase activity was inhibited by ammonia (96%) and nitrate (65%). Fixation was greatest when Ctenocladus balls were incubated anaerobically in the light with sulfide. Dark anaerobic fixation was not stimulated by organic substrates in short-term (4-h) incubations, but was in long-term (67-h) ones. Areal estimates of benthic N2 fixation were measured seasonally, using chambers. Highest rates (-29.3 ,umol of C2H4 m2 h 1) occurred under normal diel regimens of light and dark. These estimates indicate that benthic N2 fixation has the potential to be a significant nitrogen source in Mono Lake.

Meromixis in hypersaline Mono Lake, California. 2. Nitrogen fluxes

“…Although nitrogen fixation is low or absent in the pelagic region, it does occur in the sur-ficiral sediments and floating ball-shaped clusters consisting of a matrix of filamentous chlorophytes, nonheterocystous cyanobacteria, and anaerobic bacteria (Oremland 1990) found in the littoral region. Oremland (1990) found benthic N-fixation rates of -6 pmol me2 h-l and estimated lakewide fixation to be -0.1 x 10" mol yr-' or 0.6 mmol m-2 yr-I. Subsequent measurements of nitrogen fixation in benthic algal mats have yielded rates -lo-fold higher (65 pmol m-* h-l, D. Herbst pers.…”

“…comm.). The highest hourly rate multiplied by 24 h and the total area of sediments ablove 1 O-m depth (57 km2) yields a lakewide (160 km2) input of 0.5 mmol m-* d-l. Because algal mats are patchily distributed, a major portion of the benthic fixation is light-dependent (Oremland 1990), and rates measured by Herbst were measured at temperatures near the annual maximum in well-developed mats; a realistic mean estimate is much less. Realized rates are likely to be not more than a tenth of this estimate or 0.05 mmol m-2 d-l.…”

Chemolithotrophic haloalkaliphiles from soda lakes

“…The soda lakes are populated almost exclusively by prokaryotes, which can form dense communities (possibly due to the absence of grazing pressure) even in saturated alkaline brines [6][7][8][9][10][11]. Alkaliphilic cyanobacteria (Spirulina, Arthrospira, Anabaenopsis, Cyanospira) are responsible for the generally high level of primary production and nitrogen fixation in soda lakes [12][13][14]. The polymers produced by the primary producers are degraded by the aerobic and anaerobic hydrolytics, such as haloalkaliphilic Bacillus spp.…”

“…Molecular probing, including 13 C-labelling of the DNA, of the methanotrophic population in the soda lakes of Central Asia demonstrated the ubiquitous domination and the activity of the type I methanotrophs belonging to the Methylomicrobium-Methylobacter group of the gammaproteobacteria in moderately saline soda lakes [11,19,35].…”

The nitrogen cycle in cryoconites: naturally occurring nitrification‐denitrification granules on a glacier

“…The investigation of the structure and function of microbial granules has mainly been focused on granules in wastewater treatment processes, such as methanogenic granules, anaerobic ammonium oxidation (anammox) granules and nitrification granules (Liu et al, 2010;Song et al, 2013). However, there have also been a number of previous studies investigating microbial granules in natural environments (Paerl and Carlton, 1988;Oremland, 1990;Seitz, 1993;Norlund et al, 2009;Brady et al, 2010;Elliott et al, 2014).…”