Effects of shading on photosynthesis, plant organic nitrogen uptake, and root fungal colonization in a subarctic mire ecosystem

• Published in: Botany
• Main Authors: Olsrud, Maria, Michelsen, Anders
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2009
• Subjects: Climate change; Rubus chamaemorus; Subarctic
• Online Access: http://dx.doi.org/10.1139/b09-021; http://www.nrcresearchpress.com/doi/full-xml/10.1139/B09-021; http://www.nrcresearchpress.com/doi/pdf/10.1139/B09-021

Arctic dwarf shrub ecosystems are predicted to be exposed to lower light intensity in a changing climate where mountain birch forests are expanding. We investigated how shading at 0%, 65%, and 97% affects photosynthesis, organic N uptake, C and N allocation patterns in plants, and root fungal colonization in an ericoid dwarf shrub ecosystem. The ecosystem was labeled by injection of [2- 13 C, 15 N]glycine into the soil, and the uptake of 15 N and 13 C in roots and leaves 24 h later was analysed. Fungal colonization in hair roots was determined visually. Hair root 13 C: 15 N ratios showed that dwarf shrub ecosystems are capable of taking up organic N as intact glycine both under high irradiance levels and under shaded conditions when photosynthesis is strongly reduced. The allocation of 15 N to green leaves of Rubus chamaemorus L. increased with shading, whereas the allocation of 13 C to leaves of both deciduous and evergreen plant species decreased. Species dominance was correlated with uptake of 13 C, i.e., the most productive species also took up the highest amount of glycine. The ecosystem exhibited a tendency towards lower colonization by ericoid mycorrhizal fungi and dark septate endophytes in hair roots when shaded. Thus, shading has implications for processes central to both C and N cycling in subarctic ecosystems. This should be considered in projections of ecosystem responses to climate change and expanding mountain birch forests.