Seasonal variation of leaf ecophysiological traits within the canopy ofQuercus petraea(Matt.) Liebl. trees

Abstract

Facing contrasting light regimes during a vegetation season and depending on canopy position, physiological plasticity of leaves is vital for tree species to sustain the optimal ratio between the benefit of carbon assimilation and the costs of photoprotection in a given leaf. We tested the seasonal adjustment of sun and shade leaf photochemistry of sessile oak (Quercus petraea (Matt.) Liebl.) to changing light environments by parallel investigation of the meteorological conditions, photosynthetic pigment content, PSII quantum efficiency and excitation energy quenching. Sun and shade leaves got adapted to their prevailing light regimes till mid of May. High LMA was a favourable trait in avoiding water loss and decreasing photoinhibition in both flushing and sun leaves, while low LMA optimized the light absorbing leaf surface in the lower canopy layer. Partitioning of excitation energy dissipation pathyways that is PSII photochemistry-Y(II), regulated-Y(NPQ) and non-regulated-Y(NO) quenching changed significantly during leaf ontogeny and with the position of leaves in the canopy. At 800 μmol m(-2) s(-1)Y(II) < Y (NO) < Y (NPQ) was characteristic to early developmental stage of leaves from both canopy layers and to mature shade leaves, and Y(NO) < Y (II) < Y (NPQ) to mature sun leaves but the magnitude of Y(NPQ) and violaxanthin cycle activity differed in different canopy positions.

Springtime Leaf Development of Mature Sessile Oak Trees as Based on Multi-Seasonal Monitoring Data

“…Our models revealed no considerable differences in the timing of leaf unfolding and leaf expansion between the two different canopy layers. LA values at the starting point of our regression models (0 °C day) confirm that both types of leaves unfold at the same time (Poorter et al 2009, Szőllősi et al 2010, shortly before DOY 100 (the starting day used in our analysis). From that point leaves required only 3 weeks (approx.…”

“…The 30-year average of annual mean of air temperature and total rainfall was 10.2 °C and 560.5 mm, respectively ( Table 1). The growing season usually lasts from mid-April to mid-October at the site (Jakucs 1985, Szőllősi et al 2010).…”

“…Potential quantum yield of PSII photochemistry (F v /F o ) changed during the leaf maturation process and showed a saturating pattern (Babani -Lichtenthaler 1996, Szőllősi et al 2010 (Figure 1) characterized by eq. (3):…”

“…Expanding leaves of upper canopy layers affects the functioning of lower layers including certain parts of the plant's own canopy (Umeki et al 2010, Bequet et al 2011. In deciduous forests mature trees with multi-layered crown architecture are especially exposed to this shading effect (Valladares -Niinemets 2007, Mészáros et al 2007, Szőllősi et al 2010.…”

“…Plants applying this strategy of successive leaf phenology form their first leaves at the proximal end of their shoots and the leaf expansion proceeds successively to distal regions of the shoot system thus allowing the younger leaves to capture more light energy (Umeki et al 2010.). Other plant species with nearly simultaneous leaf flushing, such as a number of broad-leaved temperate woody species (Poorter et al 2009, Szőllősi et al 2010, optimize their leaf traits in order to gain the best performance (Koike et al 2001). A typical adaptive mechanism for maximal utilization of the available light energy along the vertical profile of the canopy is formation of sun and shade leaves, respectively (Jurik 1986, Givnish 1988, Yano -Terashima 2001, Terashima et al 2005, Poorter et al 2009.…”