Vertical and seasonal distribution of picoplankton and functional nitrogen genes in a high‐altitude warm‐monomictic tropical lake

Abstract

The nitrogen (N) cycle is highly dependent on microbial processes. Distribution of these communities is one of the most important factors in the variation of the N cycling in warm‐monomictic lakes. However, the effects of the alternation of water stratification and mixing periods on the ecology of microbial communities involved in these processes are rarely studied in this type of aquatic ecosystem. We explored vertical and seasonal patterns of picoplankton and the genetic potential for ammonium oxidation (amoA gene for bacteria and archaea), denitrification (nirS and nirK), anammox (hzsA), and DNRA (nrfA) and their relationships with the main limnological variables in Lake Alchichica (Central Mexican Plateau) to provide insight into the distribution and importance of these planktonic communities in warm‐monomictic tropical lakes. Ten depths were sampled during late stratification (November 2015) and mixing (February 2016) periods, covering the epilimnion, metalimnion (oxycline), and hypolimnion layers in the first case. We showed that temperature and oxygen stratification shaped the distribution of picoplankton and functional N genes in this lake. These communities also varied in relation to nutrient availability and underwent temporal changes throughout the water column. The amoA genes, along with autotrophic picoplankton, were more abundant during the stratification, indicating that nitrification could be potentially more important during this period, mainly at the oxycline layer. Denitrifying genes showed strong variations during the stratification period, with highest gene copy numbers at the oxycline and hypolimnion layers. Anoxic conditions were characterised by a relative increase in the abundance of the nrfA gene with depth, which was positively correlated with NH4+ concentration. On the other hand, the hzsA gene was not detected in any sample. Our findings highlight the importance of thermal stratification as one of the main factors influencing the genetic potential for N transformations within the water column in warm‐monomictic tropical lakes.

Processes and Microorganisms Involved in the Marine Nitrogen Cycle: Knowledge and Gaps

“…The nir genes are present in many other microorganisms, including anammox bacteria, nitrite and methane-oxidizing bacteria, AOA and AOB (Kuypers et al, 2018). Moreover, several studies have shown evidence of niche differentiation between nirK and nirS communities (Jones and Hallin, 2010;Wittorf et al, 2016;Pajares et al, 2017). Furthermore, nirS-denitrifiers seem to have a complete denitrification pathway (including nor and nos genes); thus, they are more likely to completely reduce NO 2 − to N 2 (Graf et al, 2014).…”

Short-Term Response of the Soil Microbial Abundances and Enzyme Activities to Experimental Warming in a Boreal Peatland in Northeast China

“…Our result illustrated that amoA gene abundance was negatively correlated with soil ammonia nitrogen content. The nirS and nirK genes can be used to compare the abundance and diversity of denitrifying communities [76], and these gene abundances correlate with potential denitrification rates [79,80]. In our study, the nirK gene abundance in deep soil decreased markedly under warming, and the nirK gene abundance in shallow soil and nirS gene abundance in the two soil layers tended to decrease under warming, but the changes were not statistically significant.…”

“…The nitrogen cycle depends on microbial processes and contains two important processes: nitrification and denitrification [75,76]. Studies of the nitrifiers and denitrifiers are commonly focused on functional genes, such as amoA, nirK, and nirS [75,77,78].…”

Cyanobacteria Dynamics in a Mediterranean Reservoir of the North East of Algeria: Vertical and Seasonal Variability

“…Accompanying with this gradient, we observe that the nutrients levels were greater in hypolimnetic waters than in epilimnetic ones, suggesting the presence of a vertical gradient in nutrient resources. Higher ammonium concentrations on the bottom of this reservoir could result from ammonification of organic matter and dissimilatory nitrate reduction to ammonium, which is an important N-cycling pathway, approved by anaerobic bacteria in aquatic ecosystems [Pajares et al, 2017].…”