c3.9.6 – Might trees at the treeline be sink limited?

Anfodillo T*, Carraro V, Bovo C

Dip.To TeSAF – Università di Padova, Agripolis v. Romea 16 – 35020 Padova PD
Collocazione: c3.9.6 – Tipo Comunicazione: Presentazione orale
3° Congresso SISEF *
Sessione 9: “Foreste e Cambiamento Climatico” *

Contatto: Tommaso Anfodillo (tommaso.anfodillo@unipd.it)

Abstract: The growth limitation hypothesis is currently believed to be one of the most promising mechanisms for explaining, within a global perspective, the treeline formation. At present, however, no evidence of the occurrence of sink limitation on leaf carbon uptake of high altitude trees is available. A field experiment was done in order to test whether higher temperatures might enhance sink demand, decrease needle carbon pool and, ultimately, increase stomatal conductance. On an adult Norway spruce tree growing at the treeline (2080 m a.s.l. ‘ Italian Alps) we selected a 3 m long branch. With a resistive wire rolled round the bark and applying a 130 mA current, we were able to maintain, throughout the day, a constant overheating of 10 °C (± 1.0) in order to increase the metabolic rate of the sinks. We selected 4 shoots of the heated branch and 4 of non-heated ones (control). The heating, which does not affect the measured shoots microclimate, was switched on and off for two series of measurements and stomatal conductance (gs) was measured by a steady state porometer (PMR-2 PPSystem). The heating significantly affected stomatal behaviour. After having reached the daily maximum (at approximately 7:00-7:30 a.m.), gs decreased less in heated shoots, suggesting a significative suppression of the stomata because of the increase in sink demand. Needle stomatal conductance of the heated branch was 7 to 15% higher than the control (p<0.05) during mid-morning. The effect is reversible and, when the heating was turned off, variations of gs no longer differed among shoots. Results suggest that gs of Norway spruce at the treeline is significantly sink controlled: the rate of carbon uptake is, therefore, limited by the low demand of the carbon-importing tissues. This outcome provides, also, new elements for modelling the effects of climate variations (e.g. global warming) on carbon balance of high altitude trees

Citazione: Anfodillo T, Carraro V, Bovo C (2001). Might trees at the treeline be sink limited? . 3° Congresso Nazionale SISEF, Viterbo, 15 – 18 Ott 2001, Contributo no. #c3.9.6