Carbon relations and competition between woody species in a Central European hedgerow : I. Photosynthetic characteristics.

The CO2 uptake capacity of leaves of five competing woody species in an undisturbed developing Central European hedgerow was investigated for possible factors determining competitive ability in the field. Light-saturated maximal CO2 uptake (A max) showed species-specific seasonal variations in Prunus spinosa, a bushlike pioneer on fallow land, in Crataegusxmacrocarpa and Acer campestre, two treelike species dominating the canopy, in Rubus corylifolius, a pioneer liane, and in Ribes uva-crispa, a shrubby undergrowth species. In fully-expanded sun leaves of Prunus, Crataegus and Acer A max ranged from 8 to 12 μmol m-2 s-1 while it ranged from 6 to 15 μmol m-2 s-1 in Rubus and Ribes. The temperature responses showed no difference among species. Neither leaf photosynthetic capacity nor nutrient use of carbon fixation determined competitive ability. Differences between species in the capacity of leaves to adapt to shade resulted in differences in species' establishment in the understory and demonstrated the importance of growth in order to escape light-limiting conditions. A specific sequence of species was found for the range of A max in sun leaves. It was highest in an early pioneer of low competitive ability (Rubus), medium in a later pioneer (Prunus) and in successional plants (Crataegus, Acer), and lowest in the climax species of high competitive ability, Fagus silvatica, (3-4 μmol m-2 s-1; Schulze 1970).