Nutrient regeneration mediated by extracellular enzymes in water column and interstitial water through a microcosm experiment
Song C; Cao X; Zhou Y; Azzaro M; Monticelli LS; Maimone G; Azzaro F; La Ferla R; Caruso G.;
In coastal lakes the role of microorganisms in driving nutrients regeneration at different water depths and in sediments is not yet fully understood. The dynamics of microbial (algal and bacterial) abundance and bacterial
activities involved in organic matter transformation were measured, together with nutrient concentrations, through a microcosm experiment set up using the oligotrophic Faro lake as a study model over a total period
of 15 days and with a four-day frequency. Water column at different depths (surface, middle and bottom) and interstitial water obtained by sediment centrifugation were used in appropriate ratios (mixed 1:1 with surface
waters) to fill 21-Litre plastic aquaria in order to simulate processes occurring in natural conditions. At early experimental period, the sharp decrease of dissolved organic nutrients and the abundant production of leucine
aminopeptidase (LAP) and alkaline phosphatase (AP) in correspondence with high phytoplankton abundance in bottom and interstitial water reflected the relevance of organic nutrients for inorganic nutrients regeneration
and phytoplankton growth. Size fractionation of LAP and AP as well as the positive relationship between microbial compartments suggested that bacteria and phytoplankton worked in close reciprocal synergy,
and coupling of nitrogen and phosphorus regeneration, especially in bottom and interstitial waters, was observed.
At later experimental period, the change in bacterial community, especially the increase of filamentous shaped cells, together with a simultaneous increase of protozoan abundance indicated that nutrient replenishment
made the microbial loop structure more competitive. In oligotrophic conditions, such as those in Faro lake, organic nutrient enrichment of bottom and interstitial waters was associated with changes in the bacterial
community, with consequent stimulation of extracellular enzymes to support phytoplankton growth. Nutrient availability from microbial regeneration resulted in an increased complexity of the microbial loop structure,
with bacteria and phytoplankton adopting specific strategies to respond to the changing environment
2019 - Articolo in rivista
Science of the total environment 670 (2019): 982–992. doi:10.1016/j.scitotenv.2019.03.297
Keywords: eutrophication, nutrient regeneration, Extracellular enzymatic activity, bacterial abundance, phytoplankton abundance