GROWTH-RESPONSES OF 4 SUB-ARCTIC DWARF SHRUBS TO SIMULATED ENVIRONMENTAL-CHANGE

1 Vegetative responses of Empetrum hermaphroditum, Vaccinium vitis-idaea, V. uliginosum and V. myrtillus to environmental change (temperature (T), water (W) and fertilizer (F)) were investigated in a factorial field perturbation study in sub-Arctic Sweden over two growing seasons (1991 and 1992). 2 Total above-ground biomass was largely unresponsive to the perturbations due to dilution of current season's growth by material produced in previous years. 3 The mass of shoot material produced in 1991, increased in response to F within 11 weeks of the start of the experiment in the two evergreen species (V. vitis-idaea and E. hermaphroditum), but not in the only deciduous species (V. uliginosum) measured that year. All three species studied in 1991 were unresponsive to T and W. 4 In all four species the mass of shoot material produced in 1992 showed the greatest response to F. The order of sensitivity was V. myrtillus > V. uliginosum > V. vitisidaea > E. hermaphroditum. T treatments also resulted in greater shoot mass (V. vitisidaea > E. hermaphroditum > V. myrtillus > V. uliginosum). No significant responses to W alone were observed. 5 T and F frequently interacted synergistically on the shoot characteristics measured in 1992. 6 The treatments affected the biomass allocation of the species differently, and this relates to their growth habit. Greater stem growth was observed in V. uliginosum and E. hermaphroditum, both of which spread laterally by producing long above-ground shoots. Greater leaf growth was observed in V. vitis-idaea and V. myrtillus, which spread laterally by rhizomes.