Nitrogen-addition effects on leaf traits and photosynthetic carbon gain of boreal forest understory shrubs

• Published in: Oecologia 2014-06, Vol.175 (2), p.457-470
• Main Authors: Palmroth, Sari, Holm Bach, Lisbet, Nordin, Annika, Palmqvist, Kristin
• Format: Article
• Language: English
• Subjects: Abies; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Biomass; Biomass allocation; Biomedical and Life Sciences; Boreal forests; Canopies; canopy; carbon; Carbon - analysis; Carbon dioxide; Chlorophyll; Chlorophyll content; Chlorophylls; Coniferous forests; Ecology; Ecosystem; Ecosystems; Forest ecosystems; Forest Science; Forestry; Fundamental and applied biological sciences. Psychology; General aspects; General forest ecology; Generalities. Production, biomass. Quality of wood and forest products. General forest ecology; Hydraulic properties; Hydrology/Water Resources; Leaf area; Leaves; Life Sciences; Light; Nitrogen; Nitrogen - metabolism; nitrogen content; Photosynthesis; Photosynthesis - physiology; Photosynthetic capacity; Physiological aspects; PHYSIOLOGICAL ECOLOGY; Physiological ecology - Original research; Picea abies; Pine trees; Pinus - physiology; Pinus sylvestris; Plant Leaves - physiology; Plant Sciences; Plants; Sandy soils; shade; Shrubs; Skogsvetenskap; Soil; Stomatal conductance; Sweden; trees; Trees - physiology; underground parts; Understory; Vaccinium; Vaccinium myrtillus; Vaccinium vitis-idaea; Water availability
• ISSN: 0029-8549; 1432-1939; 1432-1939
• DOI: 10.1007/s00442-014-2923-9

Boreal coniferous forests are characterized by fairly open canopies where understory vegetation is an important component of ecosystem C and N cycling. We used an ecophysiological approach to study the effects of N additions on uptake and partitioning of C and N in two dominant understory shrubs: deciduous Vaccinium myrtillus in a Picea abies stand and evergreen Vaccinium vitis-idaea in a Pinus sylvestris stand in northern Sweden. N was added to these stands for 16 and 8 years, respectively, at rates of 0, 12.5, and 50 kg N ha⁻¹ year⁻¹. N addition at the highest rate increased foliar N and chlorophyll concentrations in both understory species. Canopy cover of P. abies also increased, decreasing light availability and leaf mass per area of V. myrtillus. Among leaves of either shrub, foliar N content did not explain variation in light-saturated CO₂ exchange rates. Instead photosynthetic capacity varied with stomatal conductance possibly reflecting plant hydraulic properties and within-site variation in water availability. Moreover, likely due to increased shading under P. abies and due to water limitations in the sandy soil under P. sylvestris, individuals of the two shrubs did not increase their biomass or shift their allocation between above- and belowground parts in response to N additions. Altogether, our results indicate that the understory shrubs in these systems show little response to N additions in terms of photosynthetic physiology or growth and that changes in their performance are mostly associated with responses of the tree canopy.