3. lrradiance and Lipid Production
57
fied season in Georgian Bay, however, it seems valid to assume that the synthesis
of glycolipids, phospholipids, and total lipids over the light phase is closely
related to and only 10-15% larger than the net synthesis over the full diel cycle.
3.3. Irradiance and Lipid Synthesis
3.3.1. Photosynthetic Parameters
There are few published data on the photosynthetic parameters associated with
any of the major biomolecular classes and lipid in particular. Most of the studies
reporting on lipid synthesis by microalgae have concentrated on light-saturated
lipid production (i.e., L m ), the lipid analogue of Pm (total photosynthesis at light
saturation), or the lipid fraction of carbon fixation at light saturation (Ln/P m ).
However, much photosynthesis (and presumably, lipid synthesis) occurs at less
than light saturation and should properly be approached through analysis of the
complete light response of the phytoplankton.
Although many models for photosynthetic light response have been developed
overthe years, most of them characterize the response by use of the light-saturated
rate plus a parameter that characterizes the slope of the response at low irradiance.
This parameter is commonly termed a (Platt et aI., 1980) and is a measure of the
efficiency of light use. Ik (= Pm/a), the light adaptation parameter, is also often
used as an index of the photoadaptive state of the phytoplankton. The lipid
analogs of these parameters, a-lipid and Ik-lipid, have been used previously to
explain the production of lipid (Wainman and Lean, 1992). A final photosynthetic
parameter, ~, the slope of the light-inhibited portion of the P-I curve, may also be
required if photoinhibition is appreciable but was not needed in the data analyzed
here. All parameters reported in this chapter are chlorophyll-specific values, in
keeping with general usage.
One of the greatest problems in looking at photosynthetic lipid production is the
paucity of complete sets of lipid production versus irradiance data. For this study,
three sets of data, two from Canada and one from Germany, comprising 49
separate dates on five different bodies of fresh water, have been collected. The
first data set arises from 24 experiments on Anstruther (44° 45' N, 78° 12' W), Bay
(45° 01' N, 77° 52' W), and Jack (44° 42' N, 78° 02' W) Lakes in 1988 and has
been partially reported in Wainman and Lean (1992). The second data set comes
from eight experiments on Colpoys Bay of Lake Huron (44° 50' N, 81 ° 2' W) in
1993 (Furgal et aI., 1998; Furgal and Smith, 1997; Furgal and Smith, unpublished
data). The final data come from 16 experiments on the Schohsee (54° 15' N) in
Germany carried out in 1995 (Rai, unpublished data).
All lipid extractions were part of sequential extractions of lipid, protein, carbohydrate, and LMW. Wainman and Lean (1992) used the sequential extraction
method detailed in Cuhel and Lean (\ 987). Furgal and Smith (1997; and unpublished data) and Rai (unpublished data) used the Li and Platt method as
modified by Smith and D'Souza (1993). There is little functional difference
57
fied season in Georgian Bay, however, it seems valid to assume that the synthesis
of glycolipids, phospholipids, and total lipids over the light phase is closely
related to and only 10-15% larger than the net synthesis over the full diel cycle.
3.3. Irradiance and Lipid Synthesis
3.3.1. Photosynthetic Parameters
There are few published data on the photosynthetic parameters associated with
any of the major biomolecular classes and lipid in particular. Most of the studies
reporting on lipid synthesis by microalgae have concentrated on light-saturated
lipid production (i.e., L m ), the lipid analogue of Pm (total photosynthesis at light
saturation), or the lipid fraction of carbon fixation at light saturation (Ln/P m ).
However, much photosynthesis (and presumably, lipid synthesis) occurs at less
than light saturation and should properly be approached through analysis of the
complete light response of the phytoplankton.
Although many models for photosynthetic light response have been developed
overthe years, most of them characterize the response by use of the light-saturated
rate plus a parameter that characterizes the slope of the response at low irradiance.
This parameter is commonly termed a (Platt et aI., 1980) and is a measure of the
efficiency of light use. Ik (= Pm/a), the light adaptation parameter, is also often
used as an index of the photoadaptive state of the phytoplankton. The lipid
analogs of these parameters, a-lipid and Ik-lipid, have been used previously to
explain the production of lipid (Wainman and Lean, 1992). A final photosynthetic
parameter, ~, the slope of the light-inhibited portion of the P-I curve, may also be
required if photoinhibition is appreciable but was not needed in the data analyzed
here. All parameters reported in this chapter are chlorophyll-specific values, in
keeping with general usage.
One of the greatest problems in looking at photosynthetic lipid production is the
paucity of complete sets of lipid production versus irradiance data. For this study,
three sets of data, two from Canada and one from Germany, comprising 49
separate dates on five different bodies of fresh water, have been collected. The
first data set arises from 24 experiments on Anstruther (44° 45' N, 78° 12' W), Bay
(45° 01' N, 77° 52' W), and Jack (44° 42' N, 78° 02' W) Lakes in 1988 and has
been partially reported in Wainman and Lean (1992). The second data set comes
from eight experiments on Colpoys Bay of Lake Huron (44° 50' N, 81 ° 2' W) in
1993 (Furgal et aI., 1998; Furgal and Smith, 1997; Furgal and Smith, unpublished
data). The final data come from 16 experiments on the Schohsee (54° 15' N) in
Germany carried out in 1995 (Rai, unpublished data).
All lipid extractions were part of sequential extractions of lipid, protein, carbohydrate, and LMW. Wainman and Lean (1992) used the sequential extraction
method detailed in Cuhel and Lean (\ 987). Furgal and Smith (1997; and unpublished data) and Rai (unpublished data) used the Li and Platt method as
modified by Smith and D'Souza (1993). There is little functional difference