Variation in leaf structure and function of the Mediterranean tree Fraxinus ornus L. growing in ecologically contrasting habitats at the margin of its range

ABSTRACT

Near the northern limit of its distribution, manna ash (Fraxinus ornus L.) occupies a wide range of habitats in Hungary, and also acts as a successional pioneer. Variation in a number of leaf traits was examined in three contrasting habitats: 1) Austrian pine plantation subcanopy, 2) scrub woodland (the species' natural habitat), and 3) a grassy slope colonised by solitary F. ornus trees. While differences in leaf size and shape were moderate, leaf structure (specific leaf mass, bulk tissue density, thickness) varied substantially among populations. The quantum yield of PSII (ΦPSII), relative electron transport rate (ETR), photochemical quenching (qP), and non-photochemical energy dissipation (NPQ) were markedly higher, while PSII antenna efficiency (Fv′/Fm′) was slightly lower for solitary than for pine understorey plants. Osmotic potential at full (¹⁰⁰Ψ) and zero (⁰Ψ_π) turgor was lower (more negative), and bulk modulus of tissue elasticity (ϵ_i) was three times higher in the solitary than in the pine understorey population. Due to the spatially heterogeneous light environment, in its natural habitat F. ornus requires a plastic leaf structure and function which, in turn, contributes to the plant's successful establishment both in low- and high-light habitats.

KEY WORDS:

• bulk leaf tissue density
• chlorophyll fluorescence
• leaf morphology
• physiological plasticity
• pressure-volume analysis