What is it and what do the numbers mean? What is it and what do the numbers mean? Gary A. Ritchie Consultant in Environmental and Forest Sciences Olympia, WA Chlorophyll fluorescence

Chlorophyll Fluorescence Chlorophyll Fluorescence “...probes the light reaction of photosynthesis...”

Outline Photosynthesis Photosynthesis Chlorophyll Fluorescence (CF) measurement Chlorophyll Fluorescence (CF) measurement Interpretation Interpretation

The fate of light energy in a leaf

What happens to the absorbed light?

Three steps in photosynthesis Light harvesting (leaf “captures” light energy). Light harvesting (leaf “captures” light energy). Photochemistry (light energy converted to chemical energy in the light reaction). Photochemistry (light energy converted to chemical energy in the light reaction). Biochemistry (chemical energy used to make sugars from CO 2, Calvin Cycle). Biochemistry (chemical energy used to make sugars from CO 2, Calvin Cycle).

The light reaction

–A leaf is held in darkness for several minutes, this “empties” the electron acceptor pool and electron transport pathways. –Then the leaf is exposed to a strong pulse of photosynthetically active light. –The fluorescence emission is measured for several minutes. –The properties of this emission curve are examined and interpreted. How is CF measured?

Chlorophyll fluorescence: Discovery

“Kautsky” curve F var /F max optimal quantum yield, a direct estimate of efficiency of light reaction (Genty et al 1989) optimal quantum yield, a direct estimate of efficiency of light reaction (Genty et al 1989) Diuron

What does DCMU do?

Kautsky fluorometers In existence for many decades. In existence for many decades. Most important and often reported variable is Fv/Fm. Most important and often reported variable is Fv/Fm.

PAM fluorometers (pulse amplitude modulation) Introduced in 1995 by Schreiber et al. Introduced in 1995 by Schreiber et al. Deliver repeated saturating light pulses. Deliver repeated saturating light pulses. These swamp qP. These swamp qP. Enables separation of qP and qN components of quenching. Enables separation of qP and qN components of quenching. Provide much more useful information than Kautsky fluorometers. Provide much more useful information than Kautsky fluorometers.

Examples from Douglas-fir seedling studies –1D0 Douglas-fir seedlings –transplanted 3 blocks in raised beds on May 20, –watered, weeded and fertilized for full year. –air temp and PAR monitored continuously. –CF emissions monitored periodically with a PAM fluorometer.

Chlorophyll fluorescence: Results: Diurnal - overcast day (Oct 8, 1997)

Chlorophyll fluorescence: Results: Diurnal - sunny day (July 16, 1997)

Chlorophyll fluorescence: Results: post planting (Fv/Fm)

Chlorophyll fluorescence: Results: Post planting (qP, qN)

Chlorophyll fluorescence: Results: Cold event

Chlorophyll fluorescence: Intentionally cold-damaged Douglas-fir needles (Perks et al 2004)

Summary and interpretation Optimal quantum yield (Fv/Fm) Optimal quantum yield (Fv/Fm) –“Normal” range ~ 0.7 to 0.8. –Variability: Diurnal – low Diurnal – low Seasonal - low Seasonal - low –Only severe stress can cause a reduction in Fv/Fm.

Summary and interpretation Photochemical quenching (qP) Photochemical quenching (qP) –“Normal” range ~ 0.7 to 0.8. –Variability: Diurnal – low Diurnal – low Seasonal - moderate Seasonal - moderate –Mild stress can cause slight reduction in qP.

Summary and interpretation Non-photochemical quenching (qN) Non-photochemical quenching (qN) –“Normal range”: 0.3 to 0.7. –Variability: Diurnal – high Diurnal – high Seasonal - high Seasonal - high –Mild stress can cause large changes in qN relative to qP.

Conclusions “Kautsky” fluorometers provide relatively limited information, while PAM fluorometers analyze energy quenching. “Kautsky” fluorometers provide relatively limited information, while PAM fluorometers analyze energy quenching. Fv/Fm is robust but not sensitive – large changes in Fv/Fm indicate major stress. Fv/Fm is robust but not sensitive – large changes in Fv/Fm indicate major stress. qP is intermediate short term stress indicator. qP is intermediate short term stress indicator. qN is a very sensitive stress indicator. qN is a very sensitive stress indicator. CF emission changes can be transient. CF emission changes can be transient.

Questions?