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ADDITIONAL INDEX WORDS. CO2 assimilation, carbon balance, leaf expansion, Prunus persica, sigmoid growth ABSTRACT. Net photosynthesis, dark respiration, chlorophyll and carbohydrate content, and leaf and shoot growth of deciduous peach (Prunus persica (L.) Batsch) saplings, grown in greenhouse conditions, were measured to assess changes in carbon balance during leaf development. The 6th, 12th, and 16th leaf node were measured from the first flush at the base through expansion to maturity (the first node being the oldest). Shoot and leaves expanded following a sigmoid pattern in all nodes. The shape of the logistic curve did not vary between the 6th and the 16th leaf node, while the 12th leaf node showed a steeper response, suggesting that the latter reached 50% expansion relatively earlier. Photosynthesis varied with leaf development as young leaves had low CO2 assimilation rates that were reflected in their chlorophyll concentration. Net daily CO2 assimilation was negative in young expanding leaves. The sink-source transition, defined to be the time when the increase in daily carbohydrate exchange rate exceeded the daily increase in leaf carbohydrate content, occurred before full leaf expansion. The transition from import to export was attained 11-12 days after bud- break (corresponding to 41% to 45% of full leaf expansion) for the 6th leaf, about 7-9 days after (38% to 52% of full expansion) for the 12th leaf and after 9-10 days (32% to 38% of full expansion) for the 16th leaf. Below 30% to 50% of full expansion leaves might not respond to assimilate requirements from sinks, being sinks themselves.

Water scarcity is one of the most detrimental effects on crop yield. We studied the effect of water stress on carbon acquisition and allocation to monoterpenes of commercial importance in spearmint and rosemary plants. Increasing levels of water stress reduced photosynthesis and plant biomass. Under increasing water-stress levels photosynthesis was limited by low CO2 availability due to reduced stomatal and mesophyll conductance, while photochemical and biochemical processes were not affected. At the balsamic period, significantly higher amounts of monoterpenes per unit mass were formed in water-stressed leaves with respect to irrigated controls. However, because of plant biomass reduction, water stress reduced the total yield of monoterpenes. Appropriate irrigation strategies may, therefore, potentially improve yield of monoterpenes in field grown spearmint and rosemary crops.

International audience; The aim of this study was to monitor the effect of foliar application of humic acid on plant growth, photosynthetic metabolism and grain quality of durum wheat grown in a Mediterranean-type climate. Four fertilization treatments were applied: a non-fertilized control, a crop fertilized with foliar application of humic acid, a crop fertilized with mineral N on soil at sowing, tillering and stem elongation, and a crop fertilized with foliar application of N (ammonium-nitrate solution). Aboveground plant mass accumulation was measured throughout two growing seasons, and grain quality parameters were tested at harvest time. Gas exchange, leaf protein content and Rubisco activity were monitored at different stages of plant development. Differences between years were often relevant due to weather conditions. The foliar application of humic acid caused a transitional production of plant dry mass with respect to unfertilized control and split soil N application. This effect was also evident for grain yield, spike fertility and grain protein content during the two years of the study. Humic acid never affected photosynthesis or stomatal conductance, while Rubisco activity and leaf protein content showed intermediate responses between unfertilized control and split soil N application. We conclude that humic acid had limited promoting effects on plant growth, grain yield and quality, and photosynthetic metabolism of durum wheat crops grown in a typical Mediterranean-type agro-ecosystem of southern Italy, with respect to split soil N application.

Semi-hardwood cuttings of ‘Frantoio’ (high rooting ability) and ‘Gentile di Larino’ (low rooting ability) cultivars were obtained from 1-year-old olive shoots sampled in mid-August during the 2000 and 2001 growing season. Semi-hardwood cuttings were dipped in IBA 4000 ppm and H 2O2 (0%-control or 3.5% w/v) solutions before rooting in greenhouse equipped with an automatic mist system. At 57 and 88 days after the beginning of rooting treatments cuttings were scored for the presence of callus, roots and roots number. In both cultivars and years, the IBA 4000 + H2O2 treatment significantly modified rooting of cuttings at 57 days in comparison with IBA 4000 treatment. The positive effects of H2O2 on rooting were gradually smoothed after 88 days. At the end of the propagation cycle (88th days), cuttings treated with IBA 4000 + H2O2 had significantly higher root number in comparison with those treated with IBA 4000 alone. © 2003 Elsevier B.V. All rights reserved.

Forest@ è la rivista in lingua italiana della Società Italiana di Selvicoltura ed Ecologia Forestale (S.I.S.E.F.). Il suo obbiettivo è quello di favorire la comunicazione scientifica nel settore della ricerca forestale e ambientale. A questo fine, Forest@ mira a diffondere, garantendo tempi rapidi di pubblicazione, lavori riguardanti varie discipline afferenti alle scienze forestali e ambientali, con particolare riguardo a: selvicoltura ed ecologia forestale, ecofisiologia vegetale e forestale, conservazione delle risorse genetiche e della biodiversità forestale, utilizzazioni forestali e tecnologia del legno, pianificazione forestale e territoriale, storia forestale. Forest@ prende in considerazione le seguenti categorie di lavori: - lavori scientifici originali - rassegne scientifiche - comunicazioni brevi di ricerca - rapporti tecnici e di progetto - note tecniche e metodologiche - opinioni e commenti

Stomatal density, leaf conductance and water relations can be affected by an increase in the concentration of atmospheric CO2, and thus affect plant productivity. However, there is uncertainty about the effects of elevated CO2 on stomatal behaviour, water relations and plant productivity, owing to the lack of long-term experiments in representative natural ecosystems. In this work, variations in stomatal density and index, leaf water relations and plant biomass of semi-natural grassland communities were analysed under field conditions by comparing plants in three different experimental set-ups (natural CO2 springs, plastic tunnels and mini-FACE systems). Natural degassing vents continuously expose the surrounding vegetation to truly long-term elevated CO2 and can complement short-term manipulative experiments. Elevated CO2 concentration effects on stomata persist in the long term, though different species growing in the same environment show species-specific responses. The general decrease in stomatal conductance after exposure to elevated CO2 was not associated with clear changes in stomatal number on leaf surfaces. The hypothesis of long-term adaptive modifications to stomatal number and distribution of plants exposed to elevated CO2 was not supported by these experiments on grassland communities. Elastic cell wall properties were affected to some extent by elevated CO2. Above-ground biomass did not vary between CO2 treatments, leaf area index did not compensate for reduced stomatal conductance, and the root system had potentially greater soil exploration capacity. Considerable between-species variation in response to elevated CO2 may provide a mechanism for changing competitive interactions among plant species.

Irrigation effects on whole-plant sap flow and leaf-level water relations were characterised throughout a growing season in an experimental olive (Olea europaea L.) orchard. Atmospheric evaporative demand and soil moisture conditions for irrigated and non-irrigated olive trees were also monitored. Whole-plant water use in field-grown irrigated and rain fed olive trees was determined using a xylem sap flow method (compensation heat-pulse velocity). Foliage gas exchange and water potentials were determined throughout the experimental period. Physiological parameters responded diurnally and seasonally to variations in tree water status, soil moisture conditions and atmospheric evaporative demand. There was a considerable degree of agreement between daily transpiration deduced from heat-pulse velocity and that determined by calibration using the Penman–Monteith equation in the field. Summer drought caused decreasing leaf gas exchange and water potentials, and a progressive increase in hydraulic conductance (stronger in non-irrigated than irrigated trees), probably attributable to modifications in hydraulic properties at the soil-root interface. Negligible hysteresis, attributable to low plant capacitance, was observed in the relationship between leaf water potential and sap flow. A proportional decrease in maximum daily leaf conductance with increasing vapour pressure deficit was observed, while mean daytime canopy stomatal conductance decreased with the season. As a result, plant water use was limited and excessive drought stress prevented. Non-irrigated olive trees recovered after the summer drought, showing a physiological behaviour similar to that of irrigated trees. In addition to physiological and environmental factors, there are endogenous keys (chemical signals) influencing leaf level parameters. Olive trees are confirmed to be economical and sparing users of soil water, with an efficient xylem sap transport, maintenance of significant gas exchange and transpiration, even during drought stress.

We review the literature dealing with mediterranean climate, vegetation, phenology and ecophysiology relevant to the understanding of tree-ring formation in mediterranean regions. Tree rings have been used extensively in temperate regions to reconstruct responses of forests to past environmental changes. In mediterranean regions, studies of tree rings are scarce, despite their potential for understanding and predicting the effects of global change on important ecological processes such as desertification. In mediterranean regions, due to the great spatio-temporal variability of mediterranean environmental conditions, tree rings are sometimes not formed. Often, clear seasonality is lacking, and vegetation activity is not always associated with regular dormancy periods. We present examples of tree-ring morphology of five species (Arbutus unedo, Fraxinus ornus, Quercus cerris, Q. ilex, Q. pubescens) sampled in Tuscany, Italy, focusing on the difficulties we encountered during the dating. We present an interpretation of anomalies found in the wood structure and, more generally, of cambial activity in such environments. Furthermore, we propose a classification of tree-ring formation in mediterranean environments. Mediterranean tree rings can be dated and used for dendrochronological purposes, but great care should be taken in selecting sampling sites, species and sample trees.

Scarce water resources frequently limit crop production in semi-arid lands. Drip irrigation may constitute a method for sagacious management of water resources, but there is still limited information on its use for sugar beet crop in Mediterranean environments. The present study was conducted to determine the effect of irrigation on sucrose accumulation and root yield, as well as on sugar beet physiological responses, and to compare drip and low-pressure sprinkler (high efficiency) irrigation performances for sugar quality. As the main scope of the study was to give indications to allow water saving, the comparison focused on the best irrigation method when a similar amount of water was applied. Sugar beets were grown in an experimental field site in southern Italy (Molise Region) for two consecutive growing seasons (1999/2000 and 2000/2001). The water applied ranged from 50, 75, and 100% of the estimated evapotranspiration (ET); unirrigated sugar beets were taken as control plants. In both years, harvest was completed in two periods. Increasing volume of water replaced was advantageous for crop performances, and yield and physiological responses of sugar beets drip irrigated with 75% of estimated ET matched in most cases those of low-pressure sprinkler irrigated with 100% of estimated ET, resulting in potential 25% of water volume saving. In general, drip irrigation influenced positively many of the considered physiological and technological parameters, as compared to low-pressure sprinkler irrigation. Differences in root production and sugar quality between the two harvest periods were not significant. Results indicate that (1) increasing the amount of water applied gives benefits in terms of sugar beet root yield and sucrose accumulation, (2) drip irrigation (even applied every-other-furrow) appears to be consistently advantageous with respect to low-pressure sprinkler irrigation for sugar beet performances in semi-arid environments, (3) there are indications that suggest sugar beet growers should harvest in advance (of traditional harvest dates).

Seasonal changes in hydraulic properties and tissue elasticity were evaluated in Erica arborea L., Myrtus�communis L. and Juniperus communis L., three Mediterranean shrubs that differ in adaptations to drought. These parameters were analysed over 12 months under field conditions, by comparing plants grown in the proximity of a natural CO2 spring (about 700 μmol mol–1 atmospheric CO2 concentration, [CO2]) with plants in ambient conditions. Plants at the CO2-spring site have been growing for generations at elevated [CO2]. At both sites, stem hydraulic and structural properties followed the prevailing climatic constraints. However, these shrub species co-occurring in the same environment differed in their capacity to tolerate water deficits, in xylem efficiency, and in strategies for regulating water movement between plant compartments. Either an increase or a decrease in tissue elasticity was effective in promoting resistance to drought stress, depending on the species. Long-term elevated [CO2] influenced all the studied parameters. Species-dependent differences existed in hydraulic architecture between the CO2-spring plants and control plants of E. arborea and M. communis, while J. communis plants rarely showed differences between sites. Less distinct differences between sites were observed for wood structure. The three species showed somewhat lower tissue elasticity under elevated [CO2], in particular during stress periods. The effects of elevated [CO2] on stem hydraulic pathway and structure and shoot elastic properties persist in the long term, but differ in absolute values and sign among the studied species and with the seasonal course, and thus might alter competitive relations between these shrubs.

Altres ajuts: CICYT/CLI99-0479 Altres ajuts: CICYT/REN-2000-0278/CLI We studied carbon-based secondary and structural compounds (CBSSCs) in Myrtus communis, Erica arborea, and Juniperus communis co-occurring in a natural CO2 spring site and in a nearby control site in a Mediterranean environment. Leaf concentrations of phenolics and CBSSCs, such as lignin, cellulose, and hemicellulose, total nonstructural carbohydrates (TNCs), and lipids were measured monthly (phenolics) and every two months (the other compounds) throughout a year. There was a slight seasonal trend towards maximum concentrations of most of these CBSSCs during autumn-winter and minimum values during the spring season, particularly in Myrtus communis. For most of the CBSSCs and species, there were no consistent or significant patterns in response to the elevated [CO2] (c. 700 μmol mol−1) of the spring site. These results were not due to a dilution effect by increased structural or nonstructural carbon. Therefore, in contrast to many experimental studies of CO2 enrichment, mainly conducted for short periods, there were no greater concentrations of phenolics, and, as in many of these studies, there were neither greater concentrations of the other CBSSCs. These results do not agree with the predictions of the carbon source-sink hypotheses. Possible causes of this disagreement are discussed. These causes include the complex heterogeneous environmental conditions and the variability of resource availabilities in the field, photosynthetic down-regulation, and/or the homeostatic and evolutionary nature of organisms. These results suggest evolutionary adaptive responses to changes in CO2. They also suggest caution in attributing increased CBSSC concentrations to elevated [CO2] at long-term scale in natural conditions, and therefore in their implications for plant-herbivore interactions and for decomposition.

Seasonal changes in hydraulic properties and vulnerability to xylem embolism of Erica arborea L., Myrtus communis L. and Juniperus communis L. were analysed by comparing plants at two locations in a Mediterranean environment. A distinct atmospheric CO2 concentration ([CO2]) gradient exists between the two sites with higher [CO2] in the proximity of a natural CO2 spring (700 mol mol–1). Changes in native embolism in E. arborea and M. communis indicated rather clear seasonal segregation by species and by the growth [CO2]. J. communis had constantly lower percentage embolism than the other two species (the effect of site being not consistent). Differences in summer embolism among species and between sites were in accordance with vulnerability curves. Volumetric fractions also showed seasonal and site-dependent changes. Mean specific hydraulic conductivity was strongly affected by site in E. arborea and M. communis (in opposite directions). Hydraulic properties varied as a function of shoot biomass and leaf area, and the latter increased with increasing sapwood area; differences between sites were somewhat significant in M. communis. Foliage biomass increased with stem biomass; E. arborea had higher values of foliage biomass at similar values of stem biomass at the control site. Altering branch biomass allocation may influence or not (depending on the species) hydraulic adjustment. Plant responses to resource imbalances caused by increasing [CO2] tend to compensate for the imbalance by changes in hydraulic properties and biomass allocation. However, the plasticity or compensation ability of any particular species appears limited, and effective compensation for large changes in resource balance caused by environmental forcing factors may require changes in species composition.

density and degree of sclerophylly) showed sitedependent variations, but degree and sign of such Annual variations in the water relations and stomatal changes varied with the species and/or the season. response of Erica arborea, Myrtus communis and Measurements of discrimination against 13C provided Juniperus communis occurring at a natural CO 2 vent evidence for long-term decreases of water use efficiwere analysed under Mediterranean field conditions. ency in CO 2 spring plants. Analysis of C isotope comA distinct gradient of CO 2 concentration ([CO 2 ]) exists position suggested that a downward adjustment of between two sites near a natural CO 2 -emitting vent, photosynthetic capacity may have occurred under with higher [CO 2 ] (700 mmol mol−1) in the proximity of elevated [CO 2 ]. Elevated [CO 2 ] effects on water relathe CO 2 spring. Plants at the CO 2 spring site have been tions and leaf morphology persisted in the long term, growing for generations at elevated [CO 2 ]. At both but the three shrubs growing in the same environment sites, maximum leaf conductance was related to pre- showed species-specific responses. dawn shoot water potential. The effects of water deficits during the summer drought were severe. Leaf Key words: Mediterranean shrubs, natural CO 2 springs, conductance and water potential recovered after stomatal conductance, stomatal density, water relations, major rainfalls in September to predrought values. water use efficiency. Strong relationships between leaf conductance, predawn water potential, and leaf-specific hydraulic res- Introduction istance are consistent with the role of stomata in regulating plant water status. Considerable between- Evergreen sclerophylls are regarded as one of the most species variation in sensitivity of water potentials and typical components of the Mediterranean-type vegetation stomatal characters to elevated [CO 2 ] were observed. (Specht, 1969; Kummerow, 1973; Krause and Common to all the shrubs were a reduction in leaf Kummerow, 1977). Due to the greenhouse gas-driven conductance and an increase in water potentials in predicted increase in mean global temperature at the response to elevated [CO 2 ]. Elevated [CO 2 ] decreased surface of the earth ( Kattenburg et al., 1996) and a the sensitivity of leaf conductance to vapour pressure concurrent decrease in precipitation at Mediterranean latitudes forecast by General Circulation Models, plant

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We investigated how proximity to natural CO(2) springs affected the seasonal patterns of xylem embolism in Quercus ilex L., Quercus pubescens Willd., Fraxinus ornus L., Populus tremula L. and Arbutus unedo L., which differ in leaf phenology and wood anatomy. Xylem embolism was evaluated in both artificially dehydrated branches and in hydrated apical branches collected at monthly intervals during a 20-month sampling period. Initial specific hydraulic conductivity was also evaluated. We found species-dependent differences in xylem hydraulic properties in response to elevated CO(2) concentration. Populus tremula was the most embolized and A. unedo was the least embolized of the species examined. Effects of elevated CO(2) were significant in Q. pubescens, P. tremula and A. unedo, whereas the overall response to elevated CO(2) was less evident in F. ornus and Q. ilex. Specific hydraulic conductivity differed among species but not between sites, although the interaction between species and site was significant. Differences in xylem vulnerability between trees growing near to the CO(2) spring and those growing in control areas were small. Although differences in hydraulic properties in response to elevated CO(2) concentration were small, they may be of great importance in determining future community composition in Mediterranean-type forest ecosystems. The possible causes and ecological significance of such differences are discussed in relation to elevated CO(2) concentration and other environmental conditions.