Photosynthetic characteristics of Fagus sylvatica and Quercus robur established for stand conversion from Picea abies

Efforts inEurope to convertNorway spruce (Piceaabies) plantations tobroadleaf ormixedbroadleaf-conifer forests could be bolstered by an increased understanding of how artificial regeneration acclimates and functions under a range of Norway spruce stand conditions. We studied foliage characteristics and leaflevel photosynthesis on 7-year-old European beech (Fagus sylvatica) and pedunculate oak (Quercus robur) regeneration established in open patches and shelterwoods of a partially harvested Norway spruce plantation in southwestern Sweden. Both species exhibited morphological plasticity at the leaf level by developing leaf blades in patches with an average mass per unit area (LMA) 54% greater than of those in shelterwoods, and at the plant level by maintaining a leaf area ratio (LAR) in shelterwoods that was 78% greater than inpatches.However,we observed interspecific differences in photosynthetic capacity relative to spruce canopy openness. Photosynthetic capacity (A1600, net photosynthesis at a photosynthetic photon flux density of 1600mmol photons m 2 s ) of beech in respect to the canopy gradientwas best related to leafmass, and declined substantiallywith increasing canopy openness primarily because leaf nitrogen (N) in this species decreased about 0.9 mg g 1 with each 10% rise in canopy openness. In contrast, A1600 of oak showed a weak response tomass-based N, and furthermore the percentage of N remained constant in oak leaf tissues across the canopy gradient. Therefore, oak photosynthetic capacity along the canopy gradient was best related to leaf area, and increased as the spruce canopy thinned primarily because LMA rose 8.6 g m 2 for each 10% increase in canopy openness. These findings support the premise that spruce stand structure regulates photosynthetic capacity of beech through processes that determine N status of this species; leaf N (mass basis) was greatest under relatively closed spruce canopies where leaves apparently acclimate by enhancing light harvesting mechanisms. Spruce stand structure regulates photosynthetic capacity of oak through processes that control LMA; LMAwas greatest under open spruce canopies of high light availability where leaves apparently acclimate by enhancing CO2 fixation mechanisms. Published by Elsevier B.V. * Corresponding author. Tel.: +1 662 686 3184. E-mail address: [email protected] (E.S. Gardiner).