TY - JOUR
T1 - Photosynthesis in estuarine intertidal microphytobenthos is limited by inorganic carbon availability
AU - Vieira, Sónia
AU - Sousa Dias Cartaxana, Paulo Jorge
AU - Máguas, Cristina
AU - Silva, Jorge Marques da
PY - 2016/4
Y1 - 2016/4
N2 - The effects of dissolved inorganic carbon (DIC) availability on photosynthesis were studied in two estuarine intertidal microphytobenthos (MPB) communities and in the model diatom species Phaeodactylum tricornutum. Kinetics of DIC acquisition, measured with a liquid-phase oxygen electrode, showed higher K 1/2(DIC) (0.31 mM) and Vm (7.78 nmol min-1 μg (Chl a)-1) for MPB suspensions than for P. tricornutum (K 1/2(DIC) = 0.23 mM; Vm = 4.64 nmol min-1 μg (Chl a)-1), suggesting the predominance of species with lower affinity for DIC and higher photosynthetic capacity in the MPB. The net photosynthetic rate of the MPB suspensions reached saturation at a DIC concentration of 1-1.5 mM. This range was lower than the concentrations found in the interstitial water of the top 5-mm sediment layer, suggesting no limitation of photosynthesis by DIC in the MPB communities. Accordingly, carbon isotope discrimination revealed a moderate activity of CO2-concentrating mechanisms in the MPB. However, addition of NaHCO3 to intact MPB biofilms caused a significant increase in the relative maximum photosynthetic electron transport rate (rETR max) measured by imaging pulse-amplitude modulated chlorophyll a fluorescence. These results suggest local depletion of DIC at the photic layer of the sediment (the first few hundred μm), where MPB cells accumulate during diurnal low tides. This work provides the first direct experimental evidence of DIC limitation of photosynthesis in highly productive intertidal MPB communities.
AB - The effects of dissolved inorganic carbon (DIC) availability on photosynthesis were studied in two estuarine intertidal microphytobenthos (MPB) communities and in the model diatom species Phaeodactylum tricornutum. Kinetics of DIC acquisition, measured with a liquid-phase oxygen electrode, showed higher K 1/2(DIC) (0.31 mM) and Vm (7.78 nmol min-1 μg (Chl a)-1) for MPB suspensions than for P. tricornutum (K 1/2(DIC) = 0.23 mM; Vm = 4.64 nmol min-1 μg (Chl a)-1), suggesting the predominance of species with lower affinity for DIC and higher photosynthetic capacity in the MPB. The net photosynthetic rate of the MPB suspensions reached saturation at a DIC concentration of 1-1.5 mM. This range was lower than the concentrations found in the interstitial water of the top 5-mm sediment layer, suggesting no limitation of photosynthesis by DIC in the MPB communities. Accordingly, carbon isotope discrimination revealed a moderate activity of CO2-concentrating mechanisms in the MPB. However, addition of NaHCO3 to intact MPB biofilms caused a significant increase in the relative maximum photosynthetic electron transport rate (rETR max) measured by imaging pulse-amplitude modulated chlorophyll a fluorescence. These results suggest local depletion of DIC at the photic layer of the sediment (the first few hundred μm), where MPB cells accumulate during diurnal low tides. This work provides the first direct experimental evidence of DIC limitation of photosynthesis in highly productive intertidal MPB communities.
U2 - 10.1007/s11120-015-0203-0
DO - 10.1007/s11120-015-0203-0
M3 - Journal article
C2 - 26546444
SN - 0166-8595
VL - 128
SP - 85
EP - 92
JO - Photosynthesis Research
JF - Photosynthesis Research
IS - 1
ER -