Nitrogen Fixation (Acetylene Reduction) Associated with Duckweed ( Lemnaceae ) Mats

Abstract

Duckweed (Lemnaceae) mats in Texas and Florida were investigated, using the acetylene reduction assay, to determine whether nitrogen fixation occurred in these floating aquatic macrophyte communities. N2-fixing microorganisms were enumerated by plating or most-probable-number techniques, using appropriate Nfree media. Results of the investigations indicated that substantial N2-fixation (C2H2) was associated with duckweed mats in Texas and Florida. Acetylene reduction values ranged from 1 to 18 ,umol of C2H4 g (dry weight)-' day-' for samples incubated aerobically in light. Dark N2 fixation was always twoto fivefold lower. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (7 to 10 ,uM) reduced acetylene reduction to levels intermediate between light and dark incubation. Acetylene reduction was generally greatest for samples incubated anaerobically in the light. It was estimated that 15 to 20% of the N requirement of the duckweed could be supplied through biological nitrogen fixation. N2-fixing heterotrophic bacteria (10' cells g [wet weight]-' and cyanobacteria (105 propagules g [wet weight]-1 were associated with the duckweed mats. Azotobacter sp. was not detected in these investigations. One diazotrophic isolate was classified as Klebsiella.

Dinitrogen fixation associated with shoots of aquatic carnivorous plants: is it ecologically important?

“…Plant-associated N 2 fixation has also been reported as a potential source of N for several terrestrial carnivorous plant species with opened pitcher or snapping traps (Prankevicius and Cameron, 2011;Albino et al, 2000), although direct utilization of microbially fixed N 2 by carnivorous plants has not yet been experimentally confirmed. Nitrogen-fixing bacteria have also been detected in a beneficial association with non-carnivorous aquatic plant roots and surfaces (Zuberer, 1982;Reddy, 1987).…”

Role of Internal Nutrient Storage in Duckweed Growth for Swine Wastewater Treatment

“…induced only moderate growth stimulation. In addition, the presence of N 2 -fixing heterotrophic bacteria and cyanobacteria was detected in duckweed mats sampled in Texas and Florida (Zuberer, 1982). It was estimated that as much as 15% to 20% of the nitrogen required by duckweed could come from nitrogen fixation.…”

Mutualism outcome across plant populations, microbes, and environments in the duckweedLemna minor

“…In plant-microbe mutualisms, we generally see positive correlations between host and symbiont fitness (Friesen, 2012), although some environments may decouple them (Weese et al, 2015; Shantz et al, 2016). Aquatic microbes associated with duckweed species that may affect growth are known to include diatoms (Desianti, 2012), nitrogen-fixing cyanobacteria (Zuberer, 1982; Duong and Tiedje, 1985; Eckardt and Biesboer, 1988), and a collection of additional bacteria, including members of other nitrogen-fixing clades (Underwood and Baker, 1991; Ishizawa et al, 2017b), and one that may provision phosphorus (Ishizawa et al, 2017a). Here we find positive correlations between duckweed fitness and microbial growth across treatments (Figure 3), potentially indicating positive fitness feedbacks (Sachs et al, 2004) between duckweed and the community of microbes that live on them.…”