Abstract
We have evaluated the effects of short-term changes
in incident irradiance and temperature on oxygenic
photosynthesis and oxygen consumption in a hypersaline
cyanobacterial mat from the Ebro Delta, Spain,
in which Microcoleus chthonoplastes was the dominant
phototrophic organism. The mat was incubated
in the laboratory at 15, 20, 25 and 308C at incident
irradiances ranging from 0 to 1000 mmol photons
m22 s21. Oxygen microsensors were used to measure
steady-state oxygen profiles and the rates of gross
photosynthesis, which allowed the calculation of areal
gross photosynthesis, areal net oxygen production,
and oxygen consumption in the aphotic layer of the
mat. The lowest surface irradiance that resulted in
detectable rates of gross photosynthesis increased
with increasing temperature from 50 mmol photons
m22 s21 at 158C to 500 mmol photons m22 s21 at 308C.
These threshold irradiances were also apparent from
the areal rates of net oxygen production and point to
the shift of M. chthonoplastes from anoxygenic to
oxygenic photosynthesis and stimulation of sulphide
production and oxidation rates at elevated temperatures.
The rate of net oxygen production per
unit area of mat at maximum irradiance, J0, did not
change with temperature, whereas, JZphot, the flux of
oxygen across the lower boundary of the euphotic
zone increased linearly with temperature. The rate of
oxygen consumption per volume of aphotic mat
increased with temperature. This increase occurred in
darkness, but was strongly enhanced at high irradiances,
probably as a consequence of increased rates
of photosynthate exudation, stimulating respiratory
processes in the mat. The compensation irradiance
(Ec) marking the change of the mat from a heterotrophic
to an autotrophic community, increased
exponentially
| Original language | English |
|---|---|
| Journal | Environmental Microbiology |
| Volume | 2 |
| Issue number | 4 |
| Pages (from-to) | 465-474 |
| ISSN | 1462-2912 |
| Publication status | Published - 2000 |