Chromophoric dissolved organic matter in experimental mesocosms maintained under different pCO2 levels

Abstract

Chromophoric dissolved organic matter (CDOM) represents the optically active fraction of the bulk dissolved organic matter (DOM) pool. Recent evidence pointed towards a microbial source of CDOM in the aquatic environment and led to the proposal that phytoplankton is not a direct source of CDOM, but that heterotrophic bacteria, through reprocessing of DOM of algal origin, are an important source of CDOM. In a recent experiment designed at looking at the effects of elevated pCO 2 on blooms of the coccolithophorid alga Emiliania huxleyi, we found that despite the 3 different pCO 2 levels tested (190, 414 and 714 ppm), no differences were observed in accumulation of CDOM over the 20 d of incubation. Unlike previous mesocosm experiments where relationships between CDOM accumulation and bacterial abundance have been observed, none was observed here. These results provide some new insights into the apparent lack of effect of pCO 2 on CDOM accumulation in surface waters, and question the previously proposed mechanisms and rates of CDOM production in natural phytoplankton blooms.KEY WORDS: CDOM · DOC · Mesocosms · Viruses · Cyanobacteria · Heterotrophic bacteria · CO 2 Resale or republication not permitted without written consent of the publisher

Spatio-seasonal variability of chromophoric dissolved organic matter absorption and responses to photobleaching in a large shallow temperate lake

“…7a and b) as has been shown in previous studies (e.g. Stedmon et al, 2000;Del Castillo and Coble, 2000;Yacobi et al, 2003;Rochelle-Newall et al, 2004;Zhang et al, 2007a;Kowalczuk et al, 2003).…”

Marine CDOM accumulation during a coastal Arctic mesocosm experiment: No response to elevated pCO2 levels

“…Although according to the empirical model of Stedmon and Markager [2001], at the beginning of the experiment CDOM had typical marine properties, toward the end of the experiment a nonmarine-like signatures of CDOM were apparently formed. We found significant CDOM accumulation, which contrasts findings in a previous similar experiment in temperate waters [RochelleNewall and Fisher, 2002;Rochelle-Newall et al, 2004]. However, no significant response of CDOM accumulation to different pCO 2 treatments was found.…”

“…Highest abundance of bacteria in mesocosm 3 is consistent with slightly higher increase in CDOM in the same mesocosm (Table 2). Despite the lack of evidence of different responses of CDOM to varying pCO 2 treatments, an overall accumulation of CDOM (0.0145 ± 0.0021 m À1 d À1 ) is contrary to previous mesocosm studies [ Rochelle-Newall and Fisher, 2002;Rochelle-Newall et al, 2004].…”

Mesocosm CO<sub>2</sub> perturbation studies: from organism to community level

“…It can not be ruled out that the pervasive response of the plankton community to the nutrient addition has masked possible effects caused by the CO 2 perturbations. In fact, no significant differences between CO 2 treatments were observed for PeECE II+III -concentrations of POM and DOM (Engel et al, 2004;Rochelle-Newall et al, 2004;Riebesell et al, 2007) PeECE III -phytoplankton composition and cell cycle during bloom development -inorganic nutrient utilization, nutrient stoichiometry Bellerby et al, 2007; and nutrient turnover (Tanaka et al, 2008) -biogenic calcification -bacterial abundance, diversity of attached bacteria, 14 C-leucine based bacterial production, bacteriaphytoplankton coupling -micro-zooplankton grazing -calcite loss due to microzooplankton grazing Fig. 2.…”