title: Growth response of altitudinal ecotypes of mountain birch to temperature and fertilisation.
abstract: High- and low-altitude ecotypes of mountain birch (Betula pubescens ssp. czerepanovii) showed clear differences in their responses to various experimental conditions, including two temperature regimes and four fertilisation rates. There was, however, no simple way to characterise the elevational ecotypes in terms of relative growth rate, nitrogen (N) productivity, or root N uptake rate. The leaf N concentration was generally higher in the high-altitude seedlings than in the low-altitude seedlings. At low temperature, high-altitude mountain birch maintained a relatively high growth rate by combining high root N uptake rate and high leaf N concentration with high N productivity. An increase in temperature and/or fertiliser rate resulted in a marginal increase in N productivity in the high-altitude seedlings but resulted in a strong increase in N productivity in the low-altitude seedlings. In parallel, increased temperature resulted in a pronounced decrease in leaf N concentration only in the low-altitude seedlings. Our results suggest that the weak growth response to increased temperature in high-altitude mountain birch is functionally related to high leaf N concentration. The high leaf N concentration of high-altitude mountain birch is genetically determined and has an adaptive value in a cold environment. This suggests that there is a trade-off between high N productivity at low temperature and a strong response of N productivity to temperature.
authors.affiliation: Department of Ecological Botany, University of Uppsala, Villavägen 14, SE-752 36 Uppsala, Sweden e-mail: Martin.Weih@LTO.SLU.SE Tel.: +46-18-4712853, Fax: +46-18-553419, , , , , , SE.
authors.forename: Martin
authors.initials: M
authors.lastname: Weih
authors.affiliation: Abisko Scientific Research Station, SE-981 07 Abisko, Sweden, , , , , , SE.
authors.forename: P Staffan
authors.initials: PS
authors.lastname: Karlsson
keywords: Betula pubescens ssp. czerepanovii; Growth; Key words Altitudinal ecotypes; Nitrogen productivity; Subarctic