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What factors influence in vivo chlorophyll fluorescence?
Three items that can influence the fluorescence sensitivity coefficient are:

1)    Species Composition.  The K value – calibration coefficient - is species dependent.  The ratio of chlorophyll to plant carbon can be anywhere from 25 to 100%.  Differences in cell packaging, chloroplast shape and cell morphology can also result in varying K values.

2)     Physical Environmental Parameters.  The in vivo  fluorescence efficiency of chlorophyll is dependent on light exposure and temperature.  At low light levels, algal cells can optimize the light uptake by pushing chloroplasts to the outer edge of the cell or by producing more chlorophyll per cell.  Both of these responses can result in fluorescence data that falsely represents the algal biomass.  Temperature is also a consideration.  Fluorescence is indirectly correlated to temperature.  As the temperature increases, the fluorescence decreases.  This can be corrected through temperature compensation.  The temperature coefficient for in vivo chlorophyll is 1.4%/ °C or .78%/ °F.

3)     Physiological state of the cell.  The presence of senescent cells (or dying cells) will also affect the K value.  There are three outcomes of light energy that are absorbed by chlorophyll contained in algal cells; 1) it is channeled towards photosynthesis, 2) it is given off as heat, or 3) it is re-emitted as fluorescence.  This is why healthier cells fluoresce less than senescent cells.
See our Application page for a complete description of in vivo  chlorophyll theory, measurement and calibration considerations.