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© 1996 Oxford University Press

OTHER

Variety of responses of plant phenolic concentration to CO2 enrichment

J. Pe$$$uelas1,4, M. Estiarte1, B.A. Kimball2, S.B. Idso2, P.J. Pinter, 2, G.M. Wall2, R.L. Garcia2, D.J. Hansaker2, R.L. LaMorte2 and D.L. Hensrik3

1CREAF (Centre de Recerca Ecològica i Aplicacions Forestals), Facultat de Ciències, Universitat Autònoma de Barcelona E-08 193 Bellaterra, Spain
2US Water Conservation Laboratory, Agricultural Research Service, US Department of Agriculture 4331 E. Broadway, Phoenix, AZ 85040, USA
3Western Cotton Research Laboratory, Agricultural Research Service, US Department of Agriculture 4335 E. Broadway, Phoenix, AZ 85040, USA

4To whom correspondence should be addressed. Fax: + 34 3 5811312. E-mail: penuelas@cc.uab.es

Leaf area index (LAI) of a stand of adult black alder trees (Alnus glutinosa L., Gaertn.) was determined by means of three independent methods. (1) The seasonal course of LAI was directly obtained by counting leaves in situ and adding up their areas, estimated from harvested subsamples of leaves. (2) The seasonal variation of LAI in the stand was estimated using the Li-Cor LAI-2000 PCA in parallel and with this instrument a Vegetation Area Index (VAI, projected area of all phyto-elements) was actually measured. (3) Maximum LAI was calculated from leaf litter collections taking into account specific leaf area within different layers of the alder crown. Direct LAI estimates (1) and calculations from leaf litter (3) revealed the same figure of maximum LAI (4.8). This LAI was reached in August. The LAI-2000 PCA captured the seasonal variation and underestimated, by 11% on average, the LAI obtained directly. Compared with results gained with other broad-leaved tree species the LAI-2000 PCA values for alder were reliable. It is suggested that this is due to the horizontal homogeneous structure of the main leaf layer. This is in the periphery of the crown, where 90% of the light interception occurs. Taking the het-erogeneity into account a satisfactory compatibility of the three methods applied to the alder stand was achieved.

Key words: Alnus glutinosa, leaf area index, in situ counting, LAI-2000 PCA, litter collections


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