PARENT SESSION
Poster Session #33: Light Relations.
Wednesday, August 8, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Seasonal dynamics of photosynthesis under contrasting light regimes for three Mediterranean pine species.

Awada, Tala¹, Ragoglou, Kalliopi², Fotelli, Mariantzella², Constantinidou, Helen³, ^{1 2 3}

ABSTRACT- We investigated seasonal dynamics of maximum net photosynthesis (Pn) in two-year-old seedlings of Pinus brutia, which is mainly found in the thermo-Mediterranean étage, and of P. pinea and P. pinaster which are restricted to the meso-Mediterranean étage. Seedlings were grown in pots in the field under two light regimes, sun and shade (25% of full light). Repeated measurements over a 12 month-period showed that Pn varied significantly among species and seasons. In the sun treatment, photosynthesis was low in winter, yet it remained positive all year. Following a main increase in March, species differed to when Pn peaked. Photosynthesis reached maximum in June in P. pinea (12 molm^-2s^-1), July in P. brutia (23 molm^-2s^-1) and August in P. pinaster (20 molm^-2s^-1). Photosynthetic light response curves saturated at PAR 300 molm^-2s^-1 in winter, while higher PAR reduced Pn due to photoinhibition. During summer months, Pn was not saturated at a recorded PAR of 1900 molm^-2s^-1. Minimum air temperatures of the preceding nights was apparently the main factor controlling Pn during day. Photosynthesis in shade acclimated seedlings was reduced by 50% in P. brutia and P. pinaster, but was reduced by only 20% in P. pinea. Stomatal conductance was lower in shaded seedlings than in seedlings grown in the sun, except on days with high vapor pressure deficit. Total chlorophyll content and specific leaf area increased in P. pinea in response to shade, but not in P. pinaster. P. brutia showed an increase in total chlorophyll content but not in specific leaf area. Photosynthetic and growth data indicated that P. pinaster and P. brutia are more light-demanding species than P. pinea.

KEY WORDS: Pine, Mediterranean, gas exchange, light acclimation