Photosynthetic Response to increasing Temperatures - a Comparison between prostrate and erect alpine Shrubs
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- Institutt for biologi 
As a response to climate change, shrub biomass has increased in alpine and arctic tundra ecosystems. Substantial shrub encroachment can lead to changes in carbon fluxes, due to a shift in community compositions and functional groups. Some shrub species or functional types could have advantages over others at current and future distributions, because of different characteristics such as leaf traits. To gain more knowledge about such differences and what this might mean for future species composition in the alpine environment in Norway, six different alpine shrubs were subjected to temperature regimes of 14, 17 and 22°C, during which photosynthetic and respiration rate was measured. In addition, leaf mass per area and nitrogen content was measured and compared to leaf traits from the Global Plant Trait Network. The results showed that net photosynthetic rate of all species was down-regulated, due to the substantial increase in respiration rate, at temperatures higher than 14°C. The deciduous erect shrubs Betula nana, Salix phylicifolia, S. glauca, and S. lapponum had significantly higher net photosynthetic and respiration rates at all temperatures than the prostrate shrubs Empetrum nigrum and Vaccinium vitis-idaea. However, there was no difference in how much the photosynthetic rate was down-regulated. Thus, prostrate shrubs did not have more of a disadvantage at higher temperatures, and the increase of erect shrubs in experiments observed in artificial warming experiments can therefore not be explained by different temperature responses of net photosynthetic rate alone. Rather, the higher nitrogen content and lower leaf mass per area ratio in erect shrubs could indicate greater potential to increase growth rates under more favorable conditions. In addition, respiration rate and thus net photosynthetic rate can potentially adjust under prolonged warming. The long-term effects of increased temperature on photosynthesis, growth and shrub species composition should therefore be explored further.