© 2001 Heron Publishing—Victoria, Canada
Gas exchange characteristics of a Canarian laurel forest tree species (Laurus azorica) in relation to environmental conditions and leaf canopy position
Agueda M. González-Rodríguez (1), Domingo Morales (1) and M. Soledad Jiménez (1)
1. Dpto. Biología Vegetal, Facultad de Farmacia, Universidad de La Laguna, E-38207 La Laguna, Tenerife, Spain / Received October 16, 2000
Summary
Diurnal courses of gas exchange were measured over a 1-year period in fully expanded current-year leaves in the upper (sun-exposed,
18 m above ground) and the lower (shaded, 12 m above ground) canopy of Laurus azorica (Seub.) Franco, a major canopy species of the Canarian laurel forest in Tenerife, Canary Islands, Spain. Laurus azorica exhibited high leaf plasticity in gas exchange characteristics, with a maximum carbon assimilation rate (Amax) of shade leaves about 50% that of sun leaves. This difference reflects the high leaf area index (LAI) of the stand and the
correspondingly sharp light attenuation with increasing canopy depth. In sun leaves, Amax peaked at about 11 μmol m–2 s–1 and maximum transpiration (E) was about 8 mmol m–2 s–1, which corresponded with a maximum stomatal conductance (gs) of about 650 mmol m–2 s–1. Mean maximum instantaneous water-use efficiency (WUE) was 1.5 mmol mol–1 and the mean maximum A/gs was 20–35 μmol mol–1. Mean minimum internal CO2 concentration (Ci) was 225 μmol mol–1. Although high air vapor pressure deficit (VPD) caused a small decrease in gs, it remained high enough to maintain relatively high A and E. These gas exchange characteristics indicate a non-conservative use of water, which is appropriate for a species subject
to droughts that are mild or of short duration. In this respect, Laurus azorica differs from its congener, L. nobilis L., of the Mediterranean region and other shrubs growing in Mediterranean-type climates in California and Chile that have
to withstand more severe or more prolonged droughts.
Keywords:
carbon assimilation rate, evergreen broad-leaved forest, shade leaves, stomatal conductance, sun leaves, water-use efficiency.
