Water relations, stomatal response and transpiration of Quercus pubescens trees during summer in a Mediterranean carbon dioxide spring

Abstract

Variations in water relations and stomatal response of Quercus pubescens Willd. were analyzed under Mediterranean field conditions during two consecutive summers (1993 and 1994) at two locations characterized by different atmospheric CO(2) concentrations because of the presence at one of them of a CO(2) spring. Trees at the CO(2) spring site have been growing for generations in elevated atmospheric CO(2) concentrations. The heat-pulse velocity technique was used to estimate water use of trees during a 5-month period from June to November 1994. At the end of the sap flow measurements, the trees were harvested and foliage and sapwood area measured. At both sites, maximum leaf conductance was related to predawn shoot water potential. Effects of summer drought on plant water relations, including whole-plant transpiration, were severe, but leaf conductance and water potential recovered to predrought values after major rainfall in September. Leaf conductance, predawn water potential, and sometimes sap flow, decreased in parallel with increases in hydraulic resistance, reaching a minimum in midsummer. Hydraulic resistance was higher in trees at the control site than in trees at the CO(2) spring site. The effect of elevated CO(2) concentration on leaf conductance was less at high leaf-to-air water vapor pressure difference than at low leaf-to-air water vapor pressure difference. Mean and diurnal sap fluxes were consistently higher in trees at the control site than in trees at the CO(2) spring site. During the summer period, plant water use varied between the two sites. Trees at the control site had consistently higher sap flow at corresponding values of sapwood cross-sectional area than trees at the CO(2) spring site. Because trees at the CO(2) spring site supported a smaller foliage area for a corresponding sapwood cross-sectional area than trees at the control site, the overall mean sap flux/foliage area ratio did not differ between sites. The results are discussed in terms of effects of elevated CO(2) concentration on plant water use at the organ and whole-tree scale.

Comparative stem‐growth rates of Mediterranean trees under background and naturally enhanced ambient CO2 concentrations

“…Many studies have been made in the past decade at natural CO # springs in Italy, and the observed physiological responses under elevated CO # concentration (in terms of gas exchange and water relations) have confirmed experimental evidence : lower stomatal density and stomatal index (Jones et al, 1995 ;Paoletti et al, 1998) ; reduced stomatal conductance (Bettarini et al, 1998) ; diminished superoxide dismutase activity (Schwanz & Polle, 1998) ; and smaller foliage area for a corresponding sapwood cross-sectional area (Tognetti et al, 1999). Ha$ ttenschwiler et al (1997a), through the analysis of tree-ring data from Quercus ilex trees growing around two separate natural CO # springs, reported that trees grown under high CO # for 30 yr showed a 12% greater final radial stem width than those growing at the ambient-CO # sites.…”

“…Furthermore, studies of Q. ilex and Q. pubescens at another CO # spring (called ' Bossoleto ') have indicated that the decrease in stomatal conductance caused by elevated CO # may be less evident during severe summer drought stress at high vapour pressure deficits (Tognetti et al, 1996(Tognetti et al, , 1998b(Tognetti et al, , 1999 than during periods of relatively low drought stress (Chaves et al, 1995). Quercus ilex and Q. pubescens also showed a lower foliage area at the corresponding sapwood area under elevated CO # (Tognetti et al, 1998b(Tognetti et al, , 1999. This may counterbalance the increased assimilation rate at the leaf level.…”

Reconstruction of Past Co2 Concentration at a Natural Co2 Vent Site Using Radiocarbon Dating of Tree Rings

“…The most important approaches, in order of decreasing disturbance to the ecosystems, are the closed chambers (Cotrufo et al 1998), the open top chambers (Finnan et al 2002;DeAngelis and ScarasciaMugnozza 1998), and the FACE systems (Miglietta et al 2001;Hendrey et al 1999). An important alternative to these "artificial" methods is offered by the fossil vents of C0 2 which create a "zero impact" atmospheric enrichment for the ecosystems that grow in the vicinity (van Gardingen et al 1995;Miglietta et al 1998). The activity of the geological source of carbon dioxide increases C0 2 levels in its proximity, providing a powerful tool to understand the effects of carbon dioxide on fertilization, with minor manipulation and disturbance, on a longer time scale than the simulations mentioned above.…”

“…The activity of the geological source of carbon dioxide increases C0 2 levels in its proximity, providing a powerful tool to understand the effects of carbon dioxide on fertilization, with minor manipulation and disturbance, on a longer time scale than the simulations mentioned above. The growth rates of different tree species in the C0 2 -enriched areas show different physiological responses (Jones et al 1995;Schwantz and Polle 1988;Tognetti et al 1999). AU the experiments conducted at these sites assume that the levels of exposure to the C0 2 have been constant during the growth of the plants (constant exposure hypothesis).…”

“…AU the experiments conducted at these sites assume that the levels of exposure to the C0 2 have been constant during the growth of the plants (constant exposure hypothesis). However, only brief C0 2 monitoring campaigns using infrared gas analysis (IRGA) instrumentations have been performed over the last few decades (Tognetti et al 1999(Tognetti et al ,2000Miglietta et al 1993). …”