Presence of Understory Shrubs Constrains Carbon Gain in Sunflecks by Advance‐Regeneration Seedlings: Evidence fromQuercus rubraSeedlings Growing in Understory Forest Patches with or without Evergreen Shrubs Present

• Published in: International journal of plant sciences Vol. 170; no. 6; pp. 735 - 747
• Main Authors: Nilsen, E. T., Lei, T. T., Semones, S. W.
• Format: Journal Article
• Language: English
• Published: The University of Chicago Press 01.07.2009
• Subjects: Carbon dioxide; Coniferous forests; Deciduous forests; Evergreen shrubs; Forest canopy; Leaf area; Photosynthesis; Seedlings; Shrubs; Understory
• ISSN: 1058-5893; 1537-5315
• DOI: 10.1086/599240

We investigated whether dynamic photosynthesis of understoryQuercus rubraL. (Fagaceae) seedlings can acclimate to the altered pattern of sunflecks in forest patches withRhododendron maximumL. (Ericaceae), an understory evergreen shrub. Maximum photosynthesis (A) and total CO2accumulated during lightflecks was greatest for 400‐s lightflecks, intermediate for 150‐s lightflecks, and lowest for 50‐ and 75‐s lightflecks. For the 400‐s lightflecks only, maximumAand total CO2accumulated were significantly lower for seedlings in forest patches with shrubs present (SF) than for seedlings in forest patches without shrubs (F). These effects were found only whenAwas calculated on a leaf‐area basis because the specific leaf area of seedlings in F patches was 16% lower than it was for seedlings in SF patches. Photosynthesis reached 50% induction in 159 s for seedlings in F patches compared with 226 s for seedlings in SF patches. The faster induction ofAfor seedlings in F patches resulted in a significantly higher lightfleck use efficiency than for seedlings in SF patches. The inefficient use of lightflecks byQ. rubraseedlings in SF patches may be a primary mechanism by whichQ. rubraseedlings are inhibited by subcanopy thickets ofR. maximum.