The Consequences of Sunflecks for Photosynthesis
347
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Time (hour)
Time (hour)
Fig. 17.1. Daily courses of photon flux density (left) and CO2 assimilation of Adenocaulon
hicolor leaves (right) at five different microsites in a redwood forest understory. Each was
measured on a different day (day A to E). (Pfitsch and Pearcy 1989a)
Figure 17.1 shows the daily course of PFO and assimilation on the 5 days
on which sunftecks occurred. By comparing figures for PFO and assimilation
on the left and right side, respectively, it can be seen that there is a close
correspondence between the sunftecks and peaks of photosynthetic activity.
The total daily PFO on these 5 days ranged from 0.45 (day C) to 1.93 (day
A) molm~2day~1. Sunftecks contributed from 47 (day C) to 85% (day A) of
the daily PFO but were present only 7 (day C) to 20% of the time (day E).
Most (75 to 85%) sunftecks did not exceed the PFOs required to light