Oxygenic Phototrophic Prokaryotes - Cyanobacteria and their community composition in agricultural wetlands
Plant growth and production is limited by nitrogen (N) in the reduced forms of ammonia and nitrate, which is made bioavailable during organic matter decomposition, manure in soils, through fixation of nitrogen by lightening, and via biological nitrogen fixation. N fertilizer produced by the Haber-Bosch process and phosphorus fertilizers have led to the nutrient enrichment of waterways via non point source pollution. Waterways have often been modified (e.g., impoundments) so that natural hydraulics are no longer present to flush excess nutrients and therefore harmful levels of nutrients accumulate. This coupled with rising temperatures, give Cyanobacteria and algae the ideal conditions to grow rapidly and at times produce toxins in harmful algal blooms (HABs).
However, the bad rap cyanobacteria receive is mostly due to human processes creating ideal environments for the competitive advantage of cyanobacteria growth and formation of HABs. This negativity could be balanced by understanding the reasons for the production of harmful toxins, adjustment of human processes, and knowing the tremendous benefits cyanobacteria provide. Cyanobacteria were the first organisms to produce oxygen and support the evolution of human ancestors on earth. Cyanobacteria have also been found to produce a wide range of secondary metabolites which have properties ranging from anti-cancer, anti-inflammatory, anti-bacterial, and anti-fungal properties that could lead to new medications and other advances in biotechnology.
As well, some cyanobacteria (e.g., Anabaena and Nostoc) have the ability to fix atmospheric nitrogen through specialized cells called heterocysts, which form and use a nitrogenase enzyme to fix atmospheric N when environmental N levels are too low for the requirements of photosynthesis. The ability of these nitrogen-fixing cyanobacteria has been harnessed to increase agricultural productivity in Asian rice-paddy farming and is being examined in other agricultural applications.
Within experimental agricultural wetlands, we are examining the role of the diazotrophic (nitrogen-fixing) cyanobacteria Nostoc, Anaebeana, and the diatom genera Epithemia and Rhopalodia, which contain nitrogen-fixing cyanobacterial endosymbionts. We are examining the temporal changes to the cyanobacteria communities in experimental mesocosms that have been rotated between corn growth and wetlands exposed to different hydrologic treatments. The temporary hydrologic conditions in rotational agriculture may offer a unique insight into how to harness natural ecosystem services such as the formation of heterocysts in cyanobacteria that may potentially contribute a natural form of nitrogen fertilization to crops.