Abstract
PremiseDespite great attention given to the relationship between plant growth and carbon balance in alpine tree species, little is known about shrubs at the treeline. We hypothesized that the pattern of main nonstructural carbohydrates (NSCs) across elevations depends on the interplay between phenotypic trait plasticity, plant–plant interaction, and elevation.MethodsWe studied the pattern of NSCs (i.e., glucose, fructose, sucrose, and starch) in alpine stands of Vaccinium myrtillus (above treeline) across an elevational gradient. In the same plots, we measured key growth traits (i.e., anatomical stem features) and shrub cover, evaluating putative relationships with NSCs.ResultsGlucose content was positively related with altitude, but negatively related with shrub cover. Sucrose decreased at high altitude and in older populations and increased with higher percentage of vascular tissue. Starch content increased at middle and high elevations and in stands with high shrub cover. Moreover, starch content was negatively related with the number of xylem rings and the percentage of phloem tissue, but positively correlated with the percentage of xylem tissue.ConclusionsWe found that the increase in carbon reserves across elevations was uncoupled from plant growth, supporting the growth limitation hypothesis, which postulates NSCs accumulate at high elevation as a consequence of low temperature. Moreover, the response of NSC content to the environmental stress caused by elevation was buffered by phenotypic plasticity of plant traits, suggesting that, under climate warming conditions, shrub expansion due to enhanced plant growth would be pronounced in old but sparse stands.
Highlights
PREMISE: Despite great attention given to the relationship between plant growth and carbon balance in alpine tree species, little is known about shrubs at the treeline
We studied the pattern of nonstructural carbohydrates (NSCs) in alpine stands of Vaccinium myrtillus across an elevational gradient
We found that the increase in carbon reserves across elevations was uncoupled from plant growth, supporting the growth limitation hypothesis, which postulates NSCs accumulate at high elevation as a consequence of low temperature
Summary
We studied the pattern of NSCs (i.e., glucose, fructose, sucrose, and starch) in alpine stands of Vaccinium myrtillus (above treeline) across an elevational gradient. We measured key growth traits (i.e., anatomical stem features) and shrub cover, evaluating putative relationships with NSCs. The study was carried out in the Fleons Valley, Carnic Alps (Friuli Venezia Giulia, Italy, 12°44′21′′E, 46°38′01′′N). April 2020, Volume 107 Casolo et al.—Plant traits, elevation and carbohydrates in bilberry 641 communities (Rhododendro-Vaccinion) (Mucina et al, 2016) are the shrubs Rhododendron ferrugineum and Vaccinium myrtillus and the herbs Deschampsia flexuosa, Arnica montana, Carex sempervirens, Homogyne alpina, and Solidago virgaurea subsp. Grazing of wild ungulates in the area is possible, but no evidence of direct grazing was found during the field surveys
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