Leaf Growth and Photosynthetic Performance of Two Co-existing Oak Species in Contrasting Growing Seasons

Abstract

Ecophysiological investigations of Quercus petraea and Quercus cerris were performed at the Sikfőkút research site in the dry and humid growing seasons of 2003 and 2004. The results suggested that leaf growth and the photosynthetic apparatus of Q. petraea exhibited higher sensitivity to drought in 2003 than that of Q. cerris. In leaves of Q. petraea, chlorophyll content showed larger inter-annual and within-canopy variability than in those of Q. cerris. Fully developed leaves of Q petraea showed lower SLM which indicated higher leaf cell wall elasticity allowing them to maintain a water spending strategy, while high specific leaf mass (SLM) values reflected a water saving strategy for Q. cerris. Water use efficiency of Q. cerris was higher than in the case of Q. petraea, which may provide an advantage for this species in dry periods. In the contrasting years the final leaf area and leaf mass of both species were determined by the amount of rainfall and temperature conditions during the period of early exponential phase of leaf growth. As indicated by the low values of the Fv/Fm chlorophyll fluorescence parameter the photosynthetic apparatus of both species exhibited high susceptibility to abiotic stress factors in early spring. A large VAZ cycle pool indicated that zeaxanthin dependent heat dissipation was the main contributor to photoprotection of photosynthetic apparatus in young leaves but in fully developed leaves the relatively high light saturated ETR and low Pmax as well as the maintenance of high Fv/Fm even in severe dry periods reflected the potential involvement of photorespiratory electron transport in photoprotection of both species in summer. Drought in 2003 may have resulted in serious depletion of dry matter reserves influencing the vitality of trees in following year. Q. petraea showed lower photochemical activity in the successive vegetation period after the dry year than Q. cerris which suggested lower tolerance to drought in the long term.