© 2007 Heron Publishing—Victoria, Canada
Leaf traits and tree rings suggest different water-use and carbon assimilation strategies by two co-occurring Quercus species in a Mediterranean mixed-forest stand in Tuscany, Italy
Roberto Tognetti (1, 2, 3), Paolo Cherubini (4), Susanna Marchi (5) and Antonio Raschi (2)
1. EcoGeoFor Lab, Dipartimento di Scienze e Tecnologie per l’Ambiente e il Territorio (STAT), Universitá degli Studi del Molise,
Contrada Fonte Lappone, I-86090 Pesche, Italy / 2. Istituto di Biometeorologia (IBIMET), Consiglio Nazionale delle Ricerche, Via Caproni 8, I-50145 Firenze, Italy / 3. Corresponding author (tognetti@unimol.it) / 4. WSL - Swiss Federal Institute for Forest, Snow and Landscape Research, Zürcherstrasse 111, CH-8903 Birmensdorf, Switzerland / 5. BioLabs, Scuola Superiore Sant’Anna, Viale Rinaldo Piaggio 34, I-56025 Pontedera, Italy
/ Received January 4, 2007; accepted March 21, 2007; published online September 4, 2007
Summary
We compared the water-use characteristics of co-occurring mature Quercus cerris L. and Quercus pubescens Willd. trees growing in resource-limited (mainly water) hilly habitats in Tuscany, Italy. The species differed in their distribution
along soil water gradients and in their access to, and use of, water, even though the study year was wetter than average,
though with a summer drought. Compared with Q. cerris, Q. pubescens had greater access to soil water (less negative predawn water potentials) and a more conservative water-use strategy based
on its relatively low stomatal conductance, high instantaneous water-use efficiency, less negative midday water potential
and high soil-to-leaf hydraulic conductance. Quercus cerris had less conservative water-use characteristics than Q. pubescens, exhibiting relatively high stomatal conductance, low instantaneous water-use efficiency, more negative midday water potentials
and low soil-to-leaf hydraulic conductance; however, Q. cerris had higher photosynthetic rates than Q. pubescens. Photosynthesis and stomatal conductance were positively correlated in both species. Although a strong correlation between
ring widths and precipitation patterns was not found, some dry periods influenced ring-width growth. Quercus pubescens has always grown faster than Q. cerris, probably because of more efficient water use, although stand dynamics (driven by exogenous disturbance factors, including
coppicing, browsing and competition) cannot be excluded. Ring-width variability, as well as tree-ring growth in dry years,
which should be unaffected by stand dynamics, were higher in Q. pubescens than in Q. cerris. Moreover, Q. pubescens recovered completely after the drought in the seventies, even showing higher tree-ring growth than in the recent past, whereas
Q. cerris showed a minor growth decline followed by a recovery to values comparable with those observed before the 1970s drought. Beginning
in the early eighties, tree-ring growth decreased in both species, though Q. pubescens showed consistently higher values than Q. cerris. These differences can be explained by differences in water-use efficiency. Despite differences between the species in water
use and water status, the results are consistent with the interpretation that both are drought tolerant, but that Q. pubescens is at an advantage on xeric ridges because of its greater ability to access soil water and use it more conservatively compared
with Q. cerris.
Keywords:
Mediterranean forests, oak, photosynthesis, soil-to-leaf hydraulic conductance, water potential.
