Photosynthetic characteristics and leaf carbon economy of a deciduous and an evergreen dwarf shrub: Vaccinium uliginosum L. and V. vitis-idaea L.

The seasonal course of photosynthetic rate, and light and temperature relations were studied in the dwarf shrubs Vaccinium uliginosum L., deciduous, and Vaccinium vitisidaea L., evergreen, at a subarctic site in northern Sweden, Using the photosynthetic characteristics and meteorological data from the site, the seasonal and life-span carbon dioxide gain was estimated. The photosynthetic capacity of V. uliginosum was at a maximum one month after the start of leaf expansion and declined rapidly in the beginning of September. The old V. vitis-idaea leaves needed about 2 wk to recover full photosynthetic capacity after snow-melt; the current-year V. vitis-idaea leaves needed the same time after bud-break to reach full capacity. The leaves of V. vitis-idaea showed no seasonal trend in photosynthetic capacity after the first two wk of recovery, but their capacity decreased by one third after the first winter and by approximately 10% yr^?1 over the following two yr. The seasonal variation in the photosynthetic response to temperature was more marked in V. uliginosum than in V. vitis-idaea. Light saturation occurred at approximately 3000 μmol m^?2 s^?1 in V. uliginosum and at 60 μmol m^?2 s^?1 in one-year-old V. vitis-idaea leaves. The leaves of both species had a positive carbon balance at photon flux densities above 5 μmol m^?2 s^?1. The calculated seasonal CO² gain was 21 g CO₂ g_?1 leaf in V. uliginosum and 6–8 g CO₂ g_?1 in V. vitis-idaea leaves. Life-span CO₂ gain for leaves of V. vitis-idaea was the same as in V. uliginosum, viz. 21 g CO₂ g_?1. One fifth of the CO₂ gain of V. vitis-idaea was assimilated during periods when V. uliginosum was leafless.