Photosynthetic Induction Dynamics to Sunflecks of Four Deciduous Forest Understory Herbs with Different Phenologies

Photosynthetic responses to simulated sunflecks (lightflecks) were measured in four understory herbs with a continuum of phenologies (spring green: Erythronium americanum and Podophyllum peltatum; summer green: Arisaema triphyllum and Smilacina racemosa). A light response curve was measured under natural light for each species to quantify the PPFD at light saturation, light‐saturated photosynthetic rate, light compensation point, and dark respiration. Species were compared for the PPFD required to maintain photosynthetic induction. The loss of photosynthetic induction for the three most shade‐tolerant species was determined by measuring their photosynthetic response to lightflecks following different periods in noninducing conditions. Early spring herbs, e.g., E. americanum, responded as full‐sun plants with a higher light compensation point and greater net photosynthesis at light saturation. The PPFD required to maintain an induced photosynthetic state was significantly greater in spring‐green herbs than in summer‐green herbs. Smilacina racemosa and A. triphyllum maintained a high state of induction when exposed to PPFD characteristic of an eastern North American deciduous forest understory. The loss of photosynthetic induction differed among the species. Podophyllum peltatum and S. racemosa exhibited greater inductive loss corresponding to RuBP regeneration, while A. triphyllum exhibited greater inductive loss corresponding to Rubisco inhibition and to stomatal limitations. Therefore, understory herbs of different phenologies display different photosynthetic responses to sunfleck events.