Autumnal Photosynthesis is Extended in Nitrogen-Fixing European Black Alder Compared with White Basswood/ Possible Adaptive Significance

1989

S. 12-17

1 Abb., 1 Tab., 40 Lit. Ang.

Unselbständiges Werk

200038926

Net photosynthesis was measured at weekly intervals from late September to mid-November in the field on leaves of actinorhizal European black alder (Alnus glutinosa (L.) Gaertn.) and nonactinorhizal white basswood (Tilia heterophylla Vent.) growing in central Illinois. Black alder retained its leaves and continued to photosynthesize for a month longer than white basswood. Maximum photosynthetic rate occurred in September and declines during the autumn for both species, although weekly values fluctuated widely. Mean maximum CO2 fixation rate for black alder and white basswood were 11.88 and 4.62 (Formel), respectively, at the initial measurement in late September. On each subsequent measurement date black alder had a significantly higher rate of CO2 fixation than basswood. Night temperatures of 0C and below caused a sharp decline in photosynthesis for black alder on the following da. Stomatal conductance was highly correlated with photosynthesis, but as these two parameters declined over the autumn, intercellular CO2 concentration increased. Thus, nonstomatal limitatins are thought to be involved in the temperature-induced reduction in photosynthesis. Prolonged photosynthesis in autumn may give black alder a competitive growth advantage over other deciduous species, compensate for the high energy cost associated with nitrogen fixation, or be associated with black alder's inefficient conservation of foliar nitrogen via autumnal retranslocation.