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 CO 2 gain was 21 g CO 2 g −1 leaf in V. uliginosum and 6–8 g CO 2 g −1 in V. vitis‐idaea leaves. Life‐span CO 2 gain for leaves of V. vitis‐idaea was the same as in V. uliginosum , viz. 21 g CO 2 g −1 . One fifth of the CO 2 gain of V. vitis‐idaea was assimilated during periods when V. uliginosum was leafless.