TY - JOUR

T1 - Metabolism and resources of spherical colonies of Nostoc zetterstedtii

AU - Jensen, Kaj Sand

AU - Raun, Ane-Marie Løvendahl

AU - Borum, Jens

PY - 2009

Y1 - 2009

N2 - Constraints imposed by the spherical form and gelatinous matrix of centimeter-thick colonies of thecyanobacterium Nostoc zetterstedtii on its functional properties were tested by examining the scaling of itscomposition, light absorption, photosynthesis, and respiration to individual size. In three summer experimentswith colonies collected from the bottom of oligotrophic lakes of low inorganic carbon concentrations (dissolvedinorganic C, DIC), metabolism and pigment density of colonies were scaled to their surface area as most algalfilaments were confined to a 2-mm-thick outer shell. Nostoc absorbed 96% of incident light from the surface to thecenter because of high areal pigment density, but absorbed photons were used with low quantum efficiency (11-38 mmol O2 mol21 photon) and photosynthesis was low relative to dark respiration (2.0-5.4). Therefore, N.zetterstedtii is threatened by reduced light availability and only extended to lake depths receiving about 12% ofsurface irradiance, whereas mosses, characeans, and angiosperms with thin photosynthetic tissues grew deeper(3.1-7.5% of surface irradiance). Nostoc ameliorated the restrictions of low lake DIC and long diffusion paths byactive transport that could extract most external DIC, accumulate DIC in the colony 150-fold above externalconcentrations, and retain respiratory CO2. The energy cost of solute transport and gel formation in Nostoccolonies and extensive self shading restrict their potential growth, whereas colony formation should preventgrazing and increase longevity and nutrient recirculation. Nostoc zetterstedtii has become one of rarest freshwatermacroalgae because of widespread lake eutrophication reducing water transparency and increasing competitionfrom taller and faster-growing stands of filamentous algae and higher plants.

AB - Constraints imposed by the spherical form and gelatinous matrix of centimeter-thick colonies of thecyanobacterium Nostoc zetterstedtii on its functional properties were tested by examining the scaling of itscomposition, light absorption, photosynthesis, and respiration to individual size. In three summer experimentswith colonies collected from the bottom of oligotrophic lakes of low inorganic carbon concentrations (dissolvedinorganic C, DIC), metabolism and pigment density of colonies were scaled to their surface area as most algalfilaments were confined to a 2-mm-thick outer shell. Nostoc absorbed 96% of incident light from the surface to thecenter because of high areal pigment density, but absorbed photons were used with low quantum efficiency (11-38 mmol O2 mol21 photon) and photosynthesis was low relative to dark respiration (2.0-5.4). Therefore, N.zetterstedtii is threatened by reduced light availability and only extended to lake depths receiving about 12% ofsurface irradiance, whereas mosses, characeans, and angiosperms with thin photosynthetic tissues grew deeper(3.1-7.5% of surface irradiance). Nostoc ameliorated the restrictions of low lake DIC and long diffusion paths byactive transport that could extract most external DIC, accumulate DIC in the colony 150-fold above externalconcentrations, and retain respiratory CO2. The energy cost of solute transport and gel formation in Nostoccolonies and extensive self shading restrict their potential growth, whereas colony formation should preventgrazing and increase longevity and nutrient recirculation. Nostoc zetterstedtii has become one of rarest freshwatermacroalgae because of widespread lake eutrophication reducing water transparency and increasing competitionfrom taller and faster-growing stands of filamentous algae and higher plants.

U2 - 10.4319/lo.2009.54.4.1282

DO - 10.4319/lo.2009.54.4.1282

M3 - Journal article

VL - 54

SP - 1282

EP - 1291

JO - Limnology and Oceanography

JF - Limnology and Oceanography

SN - 0024-3590

IS - 4

ER -