R. Rae et Wf. Vincent, PHYTOPLANKTON PRODUCTION IN SUB-ARCTIC LAKE AND RIVER ECOSYSTEMS - DEVELOPMENT OF A PHOTOSYNTHESIS-TEMPERATURE-IRRADIANCE MODEL, Journal of plankton research, 20(7), 1998, pp. 1293-1312
We investigated the size-dependent temperature response of natural phy
toplankton communities from a lake and a river in the Canadian subarct
ic. Photosynthesis by total, <2 mu m and >2 mu m size fractions was de
termined at 11 irradiances (1-109% of ambient solar radiation) and fiv
e temperatures (5-25 degrees C) in outdoor solar incubators. Temperatu
re had no effect on photosynthesis at low irradiance, but strongly reg
ulated the photosynthetic response at saturating and inhibiting irradi
ances. For the river phytoplankton, low temperatures lowered E-K value
s (onset of light saturation) and shifted photosynthesis in the water
column from light dependence to temperature dependence. A photosynthes
is-temperature-irradiance (P-T-E) model was developed to describe the
varied temperature response of photosynthesis across the full range of
limiting, saturating and inhibiting irradiances. The P-T-E model expl
ained 74-95% of the variation in photosynthesis for all size fractions
(total community, >2 mu m fraction and <2 mu m fraction). Picoplankto
n (<2 mu m) had greater photosynthetic rates (P-max) at all temperatur
es than did the total and >2 mu m communities. The picoplankton fracti
on was also more responsive to increasing temperature than larger cell
s, implying a greater sensitivity to diurnal or longer term changes in
lake water temperature.