FRST 200 Lecture Notes - Lecture 25: Bristlecone Pine, Shade Tolerance, Photon
Document Summary
Saturation point = ppfd needed for max photosynthesis. Typically 25-50% full sun for sun leaves. 8-15 micromol co2 m-2s-1 or less in shade leaves. Compensation point = where photosynthesis equals resp. Less in shade leaves, because they have a lower respiration rate (lower maintenance costs) **leaves/branches that, n average, are below compensation, are abscised (actively in some species = self-pruning) Leaf longevity depends on shade tolerance, available light, stress, etc. Eastern white pine ~2 seasons in white pine. Bristlecone pine - up to 45 years. High leaf angle of sun leaves reduces incident ppfd and permits light into the canopy. In combination with self-shading causes light response of whole canopy to be more. smooth, saturating at higher ppfd: sunflecks = short or long duration patches of light. Important for many understory plants and may account for 30-60% of their photosynthesis. Intensity, duration and size depend on canopy structure and height.
