TY - JOUR

T1 - Microsensor studies of photosynthesis and respiration in the larger symbiont bearing foraminifera Amphistegina lobifera, and Amphisorus hemprichii

AU - Köhler-Rink, S.

AU - Kühl, Michael

PY - 2001

Y1 - 2001

N2 - The photosynthesis and respiration of the larger foraminifera Amphistegina lobifera and Amphisorus hemprichii was studied with O2, CO2, and pH microsensors, and with a miniature gas exchange chamber. The diffusive transport of O2 and CO2 through both perforate (A. lobifera) and imperforate (A. hemprichii) calcite shells of the foraminifera was fast and allowed investigations of endosymbiont photosynthesis by microsensor measurements at the shell surface. Gross photosynthesis versus scalar irradiance (P vs. E0) curves showed onset of light saturation (Ek) at 95-198 pmol photons m-2 s-1. No photoinhibition was observed up to an irradiance of 2000 pmol photons m-2 s-1. Net photosynthesis (at saturating irradiance) and dark respiration rates were 3.7-22.7 and 5.6-14.3 nmol O2 foraminifer-1 h-1, respectively. Simultaneous CO2, pH and O2 measurements at the shell surface of A. hemprichii during experimental light-dark cycles showed rapid concentration changes of all three variables upon light-dark or dark-light shifts. The dynamics of O2 and CO2 at the shell surface of A. hemprichii showed unequal net conversion rates of O2 and CO2 during experimental light-dark cycles. The molar O2/CO2 conversion ratio at the shell surface of the foraminifera was ~2 in darkness and ~6 at saturating irradiance, pointing to a large internal supply of CO2 in the host-symbiont association and the use of bicarbonate as source for inorganic carbon. The carbonate chemistry in the vicinity of symbiont-bearing larger foraminifera is thus strongly affected by the combined action of photosynthesis, respiration and calcification, and cannot be considered in equilibrium with the surrounding sea water. This has important implications for paleoenvironmental analysis and interpretation of the stable isotope composition of foraminiferal calcite shells and the derived models used for reconstructing climate and productivity in the past.

AB - The photosynthesis and respiration of the larger foraminifera Amphistegina lobifera and Amphisorus hemprichii was studied with O2, CO2, and pH microsensors, and with a miniature gas exchange chamber. The diffusive transport of O2 and CO2 through both perforate (A. lobifera) and imperforate (A. hemprichii) calcite shells of the foraminifera was fast and allowed investigations of endosymbiont photosynthesis by microsensor measurements at the shell surface. Gross photosynthesis versus scalar irradiance (P vs. E0) curves showed onset of light saturation (Ek) at 95-198 pmol photons m-2 s-1. No photoinhibition was observed up to an irradiance of 2000 pmol photons m-2 s-1. Net photosynthesis (at saturating irradiance) and dark respiration rates were 3.7-22.7 and 5.6-14.3 nmol O2 foraminifer-1 h-1, respectively. Simultaneous CO2, pH and O2 measurements at the shell surface of A. hemprichii during experimental light-dark cycles showed rapid concentration changes of all three variables upon light-dark or dark-light shifts. The dynamics of O2 and CO2 at the shell surface of A. hemprichii showed unequal net conversion rates of O2 and CO2 during experimental light-dark cycles. The molar O2/CO2 conversion ratio at the shell surface of the foraminifera was ~2 in darkness and ~6 at saturating irradiance, pointing to a large internal supply of CO2 in the host-symbiont association and the use of bicarbonate as source for inorganic carbon. The carbonate chemistry in the vicinity of symbiont-bearing larger foraminifera is thus strongly affected by the combined action of photosynthesis, respiration and calcification, and cannot be considered in equilibrium with the surrounding sea water. This has important implications for paleoenvironmental analysis and interpretation of the stable isotope composition of foraminiferal calcite shells and the derived models used for reconstructing climate and productivity in the past.

M3 - Journal article

VL - 55

SP - 111

EP - 122

JO - Marine Biology Research

JF - Marine Biology Research

SN - 1745-1000

IS - 2

ER -