No abstract

No abstract

Br å then V. T. Gonz á lez (victoria.gonzalez@uit.no), O. Junttila, B. Lindg å rd, R. Reiersen and A. Br å then, Batatasin-III (3,3-dihydroxy-5-methoxybibenzyl) is a phenolic compound associated with the allelopathic eff ect of the evergreen dwarf shrub Empetrum nigrum , and has been referred to as the causal factor for the species being successful in dominating extensive ecosystems. Yet, only a few plant species have been tested for their response to batatasin-III, and little is known about whether environmental factors modify this allelopathic eff ect. In this study, we tested the inhibitory eff ect of purifi ed batatasin-III through bioassays on 24 vascular plant species and, for certain species, we tested if this eff ect depended on growth substrate (mineral vs organic substrate), pH, and fertilization. Moreover, we tested if batatasin-III predicted the allelopathic eff ect of E. nigrum by analyzing the inhibitory eff ect of E. nigrum leaves and humus in relation to their batatasin-III content. Our results confi rmed batatasin-III as a stable compound capable of inhibiting germination and/or mean root elongation in all of the tested species, but this eff ect was modifi ed by growth substrate. Surprisingly, the measured batatasin-III content of E. nigrum leaves (mean value 19.7 Ϯ 10.8 (SE) mg g Ϫ1 ) and humus (mean value of 1 Ϯ 1.5 (SE) μ g g Ϫ1 ) did not predict the inhibitory eff ect on mean root elongation. Although batatasin-III was found to be phytotoxic to all the tested species, we conclude that this substance alone should not be used as a proxy for the allelopathic eff ect of E. nigrum .

Climate change is modifying temperature and precipitation regimes across all seasons in northern ecosystems. Summer temperatures are higher, growing seasons extend into spring and fall and snow cover conditions are more variable during winter. The resistance of dominant tundra species to these season-specific changes, with each season potentially having contrasting effects on their growth and survival, can determine the future of tundra plant communities under climate change. In our study, we evaluated the effects of several spring/summer and winter climatic variables (i.e., summer temperature, growing season length, growing degree days, and number of winter freezing days) on the resistance of the dwarf shrub Empetrum nigrum. We measured over six years the ability of E. nigrum to keep a stable shoot growth, berry production, and vegetative cover in five E. nigrum dominated tundra heathlands, in a total of 144 plots covering a 200-km gradient from oceanic to continental climate. Overall, E. nigrum displayed high resistance to climatic variation along the gradient, with positive growth and reproductive output during all years and sites. Climatic conditions varied sharply among sites, especially during the winter months, finding that exposure to freezing temperatures during winter was correlated with reduced shoot length and berry production. These negative effects however, could be compensated if the following growing season was warm and long. Our study demonstrates that E. nigrum is a species resistant to fluctuating climatic conditions during the growing season and winter months in both oceanic and continental areas. Overall, E. nigrum appeared frost hardy and its resistance was determined by interactions among different season-specific climatic conditions with contrasting effects.