123
environment and can be unambiguously assigned to specific physiological responses of the
organism. The success of this type of experiment depends critically on the presence of control
samples, to which the responses of the treated samples can be compared. A lack of suitable
controls is one of the main factors which limits the interpretation of fluorescence techniques
in field samples. Considering the number of environmental factors that potentially influence
photosynthesis, and the complex coupling of these reactions to fluorescence yield, an
unambiguous assignment of field fluorescence measurements to specific environmental
influences and physiological responses is nearly impossible without additional information.
This is not to say that field measurements of in vivo or in situ chlorophyll fluorescence are
useless. There are excellent examples of studies that have used correlations between
fluorescence measurements and other physical and biological variables, such as natural
gradients in light or nutrient availability, to assess phytoplankton responses (Vincent, 1980;
Kolber et ai., 1989; Therriault et ai., 1989; Cleveland et ai., 1989; Yentsch and Campbell,
1991; Olson et ai., 1989a). Powerful new fluorescence techniques, such as the "double-flash"
technique used by Falkowski and co-workers (see below), also appear to be quite useful in
evaluating many aspects of photosynthetic physiology. One additional technique, which
remains to be explored, involves the use of field samples as controls against which aliquots
of the same sample briefly incubated with added nutrients, metabolic inhibitors, or under
various light conditions, can be compared. Under these conditions, one could potentially
evaluate the bulk properties of a field sample in terms of the relative importance of multiple
environmental factors that affect photosynthetic physiology.
Fluorescence excitation and emission spectra. A fluorescence emission spectrum probes the
spectral properties of those pigments that directly emit fluorescence. Since the origin of
fluorescence emission in nearly all photosynthetic algae and higher plants is the chI a antenna
of PS II, emission spectra are of little use in distinguishing between the photosynthetic
properties of samples. The exception is the phycobilin-containing algae, where a significant
fraction of total fluorescence emission originates from the phycobilisome antenna (Bryant,
1986). This factor has been utilized to evaluate the abundance and distribution of marine
Synechococcus species (Olson et ai., 1989a).
environment and can be unambiguously assigned to specific physiological responses of the
organism. The success of this type of experiment depends critically on the presence of control
samples, to which the responses of the treated samples can be compared. A lack of suitable
controls is one of the main factors which limits the interpretation of fluorescence techniques
in field samples. Considering the number of environmental factors that potentially influence
photosynthesis, and the complex coupling of these reactions to fluorescence yield, an
unambiguous assignment of field fluorescence measurements to specific environmental
influences and physiological responses is nearly impossible without additional information.
This is not to say that field measurements of in vivo or in situ chlorophyll fluorescence are
useless. There are excellent examples of studies that have used correlations between
fluorescence measurements and other physical and biological variables, such as natural
gradients in light or nutrient availability, to assess phytoplankton responses (Vincent, 1980;
Kolber et ai., 1989; Therriault et ai., 1989; Cleveland et ai., 1989; Yentsch and Campbell,
1991; Olson et ai., 1989a). Powerful new fluorescence techniques, such as the "double-flash"
technique used by Falkowski and co-workers (see below), also appear to be quite useful in
evaluating many aspects of photosynthetic physiology. One additional technique, which
remains to be explored, involves the use of field samples as controls against which aliquots
of the same sample briefly incubated with added nutrients, metabolic inhibitors, or under
various light conditions, can be compared. Under these conditions, one could potentially
evaluate the bulk properties of a field sample in terms of the relative importance of multiple
environmental factors that affect photosynthetic physiology.
Fluorescence excitation and emission spectra. A fluorescence emission spectrum probes the
spectral properties of those pigments that directly emit fluorescence. Since the origin of
fluorescence emission in nearly all photosynthetic algae and higher plants is the chI a antenna
of PS II, emission spectra are of little use in distinguishing between the photosynthetic
properties of samples. The exception is the phycobilin-containing algae, where a significant
fraction of total fluorescence emission originates from the phycobilisome antenna (Bryant,
1986). This factor has been utilized to evaluate the abundance and distribution of marine
Synechococcus species (Olson et ai., 1989a).