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The influence of iron, siderophores and refractory DOM on cyanobacterial biomass in oligotrophic lakes
Author(s) -
Sorichetti Ryan J.,
Creed Irena F.,
Trick Charles G.
Publication year - 2014
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/fwb.12355
Subject(s) - nitrate , phytoplankton , environmental chemistry , cyanobacteria , dissolved organic carbon , siderophore , chlorophyll a , ammonium , nutrient , phosphorus , biomass (ecology) , chemistry , biology , ecology , botany , bacteria , genetics , organic chemistry
Summary Our conceptual understanding of factors that promote cyanobacterial growth is inadequate in the face of rising public concern about cyanobacterial blooms in oligotrophic freshwater lakes. We hypothesised that cyanobacterial density would be highest in lakes with low levels of phosphorus ( P ), nitrogen ( N ), total dissolved iron ( TDF e) and dissolved organic matter ( DOM ) with labile properties, where cyanobacteria use siderophores to scavenge F e and overcome F e limitation. We tested this hypothesis by measuring cyanobacterial density during peak biomass in 25 oligotrophic lakes representing gradients in total P ( TP ), nitrate, TDF e and DOM concentrations. Total phytoplankton biomass, using chlorophyll‐ a (chl‐ a ) as a proxy, was a function of TP ( r 2 = 0.83, P < 0.001). Cyanobacterial density was highest in lakes with low chl‐ a , low TP , variable (low and high) nitrate and low TDF e. Regression tree analysis confirmed that TDF e, specifically low concentrations (<3.2 μg L −1 ), gave rise to the highest cyanobacterial densities in lakes. All lakes had detectable concentrations of hydroxamate and/or catecholate siderophores. In lakes with relatively low TDF e (<3.2 μg L −1 ), cyanobacterial density was positively correlated with hydroxamate siderophore concentration ( r 2 = 0.77, P = 0.01). In lakes with higher TDF e (≥3.2 μg L −1 ), cyanobacterial density was positively correlated with nitrate ( r 2 = 0.84, P < 0.001) and ammonium ( r 2 = 0.75, P < 0.001) concentrations. Dissolved organic matter may have an overriding control on cyanobacterial density, with cyanobacterial densities typically highest where DOM concentrations were low (<5 mg L −1 ) and with a humification index <5. These findings suggest that DOM with labile properties may allow cyanobacteria to gain access to F e complexed with DOM and thus to overcome F e limitation, while DOM with refractory properties may bind F e tightly so that Fe is not readily bioavailable to cyanobacteria. A new conceptual model is presented that emphasises the potential influence of DOM quantity and quality on the functioning of siderophores and the provision of a supply of Fe to cyanobacteria in lakes with low macronutrient supply.