Search

We investigated the relationship between time since death and morphological characteristics of Abies alba Mill. (European silver fir) and Fagus sylvatica L. (European beech) stumps in two forest stands in the central Apennines. At each site, 15 or 16 living trees were selected, and increment cores were collected to build master ring-width chronologies. For both sites, cross sections were collected from stumps. Samples were assigned to visually discernible decay classes, and their death date dendrochronologically determined. Using cross-dating techniques, stumps cross-dated significantly with standard chronologies, and it was possible to assign a year of death to 77% and 69% of sampled A. alba and F. sylvatica stumps, respectively. Analysis of the time since death of the stumps suggests that the two species have similar decay rates, although A. alba was faster in passing from class 2 to class 3. However, this study revealed a continuum through decay classes and showed a high variability in the transition rate from one class to another. Overall, information obtained using dendrochronological techniques was valuable for assessing deadwood decomposition rates. The variability found in stump decomposition rates indicates that existing decay classification schemes, although providing information on decomposition timing, are hardly applicable to these forest stands and that the relationship between qualitatively assessed decay classes and time since death of trees appears to be rather weak.

Data from Spanish and Italian olive orchards with different cultivars (>Manzanilla>, >Frantoio>, >Leccino>, >Razzola> and >Taggiasca>) growing in different environments (southern Spain; north, centre and south of Italy) were used to illustrate how models on water use and photosynthetic behaviour of the olive tree can be useful tools for choosing pruning intensity and canopy shape for optimum water use and carbon assimilation. Both original and published data on olive physiological behaviour were used to illustrate limitations of model performance due to both inadequate input variables and poor description of the processes involved. We observed differences on leaf water status between cultivars and locations, likely due to differences in soil characteristics related to soil matric potential and soil hydraulic conductivity. This suggests that the volumetric soil water content may not be the best variable for characterizing the soil water status when modelling, and highlights the importance of considering specific environmental conditions before extrapolating data from the literature to specific orchards. We evaluated the importance of considering the reduction in olive photosynthetic capacity under stress conditions, driven by a reduction in leaf mass per area and leaf nitrogen content. A modelling exercise was then made for a >Manzanilla> olive tree at the Spanish orchard, by combining a gas exchange model for olive leaves with a model able to simulate the spatial distribution of radiation and leaf-gas exchanges within the olive canopy as a function of canopy structure, canopy microclimate, and physical and physiological leaf properties. Simulated values for two different canopy shapes showed that a top-open spherical canopy, typical in the area, improved water use efficiency, as compared to a spherical canopy closed at the top. The model also showed the value of leaf area density that must be left after pruning for optimizing carbon assimilation relative to water consumption.

We investigated the effect of high copper (Cu) concentrations on poplar woody cuttings (Populus × euramericana) clone Adda in order to estimate the degree of metal tolerance. Metal accumulation was also investigated to determine where and to what extent Cu is stored within the plant. Plant responses to Cu were determined comparing biomass growth and photosynthetic potential measured at concentrations of 0.4 (control), 20, 100, 500 and 1000M of Cu supplied with Hoagland’s solution in an aerated hydroponic system. Results obtained in this study show that increasing levels of Cu resulted in a general reduction of plant growth at concentrations equal or higher than 100M. At these concentrations of Cu, reductions of chlorophyll contents and photosynthetic parameters were also observed. The metal was mainly accumulated in the root system at all Cu levels. Since no significant differences were noticed in growth and photosynthesis between control plants and those treated with 20M of Cu, we conclude that Adda clone was able to tolerate quite high concentration of Cu and we propose it as a good candidate for screening Cu tolerance in the field. © 2007 Elsevier B.V. All rights reserved.

The olive tree is a traditionally nonirrigated crop that occupies quite an extensive agricultural area in Mediterranean-type agroecosystems. Improvements in water-use efficiency of crops are essential under the scenarios of water scarcity predicted by global change models for the Mediterranean region. Recently, irrigation has been introduced to increase the low land productivity, but there is little information on ecophysiological aspects and quality features intended for a sagacious use of water, while being of major importance for the achievement of high-quality products as olive oil. Therefore, deficit irrigation programmes were developed to improve water-use efficiency, crop productivity and quality in a sub humid zone of Southern Italy with good winter-spring precipitation. The response of mature olive trees to deficit irrigation in deep soils was studied on cultivars Frantoio and Leccino by examining atmospheric environment and soil moisture, gas exchange and plant water status, as well as oil yield and chemical analysis. Trees were not irrigated (rainfed) or subjected to irrigation at 66% and 100% of crop evapotranspiration (ETc), starting from pit hardening to early fruit veraison. Improvements in the photosynthetic capacity induced by increasing soil water availability were only of minor importance. However, plant water status was positively influenced by deficit irrigation, with 66% and 100% of ET C treatments hardly differing from one another though consistently diverging from rainfed plants. The effect of water stress on photosynthesis was mainly dependent on diffusion resistances in response to soil moisture. Leccino showed higher instantaneous water-use efficiency than Frantoio. Crop yield increased proportionally to the amount of seasonal water volume, confirming differences between cultivars in water-use efficiency. The unsaturated/saturated and the monounsaturated/ polyunsaturated fatty acid ratios of the oil also differed between cultivars, while the watering regime had minor effects. Although irrigation can modify the fatty acid profile, polyphenol contents were scarcely affected by the water supply. Irrigation to 100% of ET C in the period August-September might be advisable to achieve high-quality yields, while saving consistent amounts of water.

We investigated the variation of wood anatomical characteristics and carbon isotopic composition of tree rings showing intra-annual density fluctuations (IADFs) in plants of Pinus pinaster Ait. growing at a coastal plantation in Tuscany (Italy). IADFs are regions of the tree ring where wood density changes abruptly due to a sudden change of environmental conditions, particularly of water availability. Dendrochronological analyses allowed dating of the rings and four regions were considered in each tree ring: earlywood, IADF, late-earlywood and latewood. Although IADF commonly has been classified as latewood-like tissue in the literature, we found differences in anatomical characteristics and carbon isotopic composition between tracheids of the two regions. The lumen area of tracheids in IADF was significantly larger than in latewood, while still smaller than in earlywood and late-earlywood. Latewood and IADF had a greater proportion of narrow tracheids than both earlywood and late-earlywood. Although latewood and IADF were characterized by tracheids with lumina lengthened in the tangential direction, while earlywood tracheids were elongated in the radial direction, some differences were found also between latewood and IADF. Moreover, IADF tracheids had a higher 13C/12C ratio than any other region and showed isotopic values significantly different from the latewood. The quantification of anatomical features of tracheids within rings was useful to discriminate between latewood and IADFs, as well as helpful for the identification of tree-ring boundaries. The overall interpretation of dendrochronological, wood anatomical and carbon isotopic data seems to be a promising approach for the dating and the ecological interpretation of tree rings in Mediterranean ecosystems and for gaining climatic information with intra-annual resolution.

1Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium; 2Dipartimento di Bioscienze e Territorio, Universita’ degli Studi del Molise, 86090 Pesche, Italy; 3School of GeoSciences, University of Edinburgh, Crew Building, West Mains Road, Edinburgh EH9 3JN, UK; 4ICREA at CREAF, Universidad Autonoma de Barcelona, Cerdanyola del Valles, Barcelona, Spain; 5Corresponding author (kathy.steppe@UGent.be)

Phenological synchronisms between apical and lateral meristems could clarify some aspects related to the physiological relationships among the different organs of trees. This study correlated the phenological phases of bud development and xylem differentiation during spring 2010-14 in balsam fir (Abies balsamea Mill.) and black spruce [(Picea mariana Mill. (BSP)] of the Monts-Valin National Park (Quebec, Canada) by testing the hypothesis that bud development occurs after the reactivation of xylem growth. From May to September, we conducted weekly monitoring of xylem differentiation using microcores and bud development with direct observations on terminal branches. Synchronism between the beginning of bud development and xylem differentiation was found in both species with significant correlations between the phases of bud and xylem phenology. Degree-day sum was more appropriate in assessing the date of bud growth resumption, while thermal thresholds were more suitable for cambium phenology. Our results provide new knowledge on the dynamics of spring phenology and novel information on the synchronisms between two meristems in coniferous trees. The study demonstrates the importance of precisely defining the phases of bud development in order to correctly analyse the relationships with xylem phenology.

Uno degli aspetti più importanti per una corretta stima dell'evapotraspirazione reale (ETa) su aree a copertura arborea rada e non uniforme è rappresentato dalla necessità di definire correttamente il contributo relativo delle diverse componenti (terreno nudo, copertura erbacea e arborea) nel corso della stagione. La disponibilità di reti di monitoraggio diverse (ecofisiologica, agrometeorologica e di Osservazione della Terra) offre l'opportunità di integrare tecniche di rilevamento in campo e tecniche di telerilevamento (Remote Sensing) al fine di migliorare la precisione e l'affidabilità dei modelli esistenti. In questo lavoro sono presentati i risultati preliminari ottenuti dall'impiego di coefficienti colturali ricavati dalle variazioni di un classico indice vegetazionale (NDVI) all'interno di un modello di bilancio idrico (WINETRO) per la stima dell'ETa di una coltura d'olivo. Le stime di evapotraspirazione combinata delle tre principali componenti (olivo, erba, suolo) e quelle della traspirazione delle piante di olivo sono state confrontate rispettivamente con i dati rilevati dai sensori d'umidità del suolo a due diverse profondità (10 e 30 cm) e con quelli di traspirazione della pianta intera (sap flow), ottenendo un significativo miglioramento della capacità del modello di seguire le relative variazioni spazio-temporali all'interno del sito pilota.

It is still unclear whether the exponential rise of atmospheric CO2 concentration has produced a fertilization effect on tropical forests, thus incrementing their growth rate, in the last two centuries. As many factors affect tree growth patterns, short -term studies might be influenced by the confounding effect of several interacting environmental variables on plant growth. Long-term analyses of tree growth can elucidate long-term trends of plant growth response to dominant drivers. The study of annual rings, applied to long tree-ring chronologies in tropical forest trees enables such analysis. Long-term tree-ring chronologies of three widespread African species were measured in Central Africa to analyze the growth of trees over the last two centuries. Growth trends were correlated to changes in global atmospheric CO2 concentration and local variations in the main climatic drivers, temperature and rainfall. Our results provided no evidence for a fertilization effect of CO2 on tree growth. On the contrary, an overall growth decline was observed for all three species in the last century, which appears to be significantly correlated to the increase in local temperature. These findings provide additional support to the global observations of a slowing down of C sequestration in the trunks of forest trees in recent decades. Data indicate that the CO2 increase alone has not been sufficient to obtain a tree growth increase in tropical trees. The effect of other changing environmental factors, like temperature, may have overridden the fertilization effect of CO2. It is still unclear whether the exponential rise of atmospheric CO2 concentration has produced a fertilization effect on tropical forests, thus incrementing their growth rate, in the last two centuries. As many factors affect tree growth patterns, short -term studies might be influenced by the confounding effect of several interacting environmental variables on plant growth. Long-term analyses of tree growth can elucidate long-term trends of plant growth response to dominant drivers. The study of annual rings, applied to long tree-ring chronologies in tropical forest trees enables such analysis. Long-term tree-ring chronologies of three widespread African species were measured in Central Africa to analyze the growth of trees over the last two centuries. Growth trends were correlated to changes in global atmospheric CO2 concentration and local variations in the main climatic drivers, temperature and rainfall. Our results provided no evidence for a fertilization effect of CO2 on tree growth. On the contrary, an overall growth decline was observed for all three species in the last century, which appears to be significantly correlated to the increase in local temperature. These findings provide additional support to the global observations of a slowing down of C sequestration in the trunks of forest trees in recent decades. Data indicate that the CO2 increase alone has not been sufficient to obtain a tree growth increase in tropical trees. The effect of other changing environmental factors, like temperature, may have overridden the fertilization effect of CO2.

There is increasing awareness that structure-based indicators should be considered for assessing the biological value of late successional forests. In order to increase the unique habitat features critical for old-growth associated species, it is important to identify and rank candidate potential forest sites on the basis of their distinctive structural features. Data on living and deadwood components for the identification of old-growth condition are usually acquired in the considered forest stands by two sampling survey: (i) census performed in relatively large monitoring sites; (ii) network of small sampling units, on which inventory practices are usually based. Several authors argued that choosing between these survey strategies might have substantial effects on the values of common indicators of old-growth condition. Our study aims at (i) assessing the total estimate differences among old-growth structural indicators measured in field plots with different sizes, and (ii) defining the optimal sample size for the reliable assessment of such indicators. The study was carried out in six beech dominated forest stands on the Apennines range in Italy. In each stand, living and deadwood components were surveyed and geocoded in 1-ha square areas. Based on these dataset, circular plots with radii ranging from 4 m up to 20 m were then considered in order to quantify the effect of sampling plot size on the estimation of four structural indicators: (1) number of living trees; (2) number of large trees (dbhP50 cm); (3) total deadwood volume; (4) number of deadwood elements (snags, dead standing trees; lying dead trees, lying deadwood)with dbh (or average diameter for lying deadwood)P30 cm. We found that the size of the sampling plots should be at least 500 m2 in order to establish a database for the assessment of the investigated indicators. The census approach should be preferred to the sampling plot approach for old-growth forest stands smaller than 3–5 ha. The achieved results contribute to define assessment protocols for characterizing and ranking the degree to which forest stands approximate old-growth condition based on standardized indicators. L'articolo è disponibile sul sito dell'editore www.elsevier.com/locate/foreco

Continuous stem water relations, sap flux and radial variation, and soil moisture were monitored in rainfed and irrigated mature olive (Olea europaea L.) trees in field conditions in central Italy. A mathematical procedure was applied to describe plant-environment dependences in order to facilitate the identification of the correspondence between stem factors (sap flow, diameter variation) and environmental parameters (water availability, evaporative demand). A direct correspondence between the time series of the monitored parameters was observed in the two growing seasons. Soil water content was synchronous to stem diameter variation in irrigated trees, while they were asynchronous in rainfed conditions. On daily basis, sap flux density showed an opposite trend with respect to patterns of VPD and ET0 in spring, corresponded to the course of ET0 in summer, and lagged behind ET0 in autumn. Maximum daily shrinkage (MDS) was correlated with VPD (R2 = 0.50, in rainfed; R2 = 0.51, in irrigated plants), whereas was not significantly related to ET0. Conversely, cumulative sap flow showed a good relationship with ET0 (R2 = 0.60, in rainfed; R2 = 0.51, in irrigated plants), and scaled exponentially with MDS (R2 = 0.56, in rainfed; R2 = 0.61, in irrigated plants) indicating consistent radial transfer of water between xylem and phloem. The proposed analytical approach highlights the importance of combining measured parameters and sensor outputs in order to determine adjustments of specific plant functionality traits, such as the dynamics of water status in trees, for modelling and practical uses. This study also indicates a different accounting of the effect of microclimatic variables on plant signals based on stem sensors.

Il cambiamento dell’uso del suolo è uno dei driver principali della riduzione della resilienza ecosistemica, così come della perdita di biodiversità e approvvigionamento di servizi. Rappresenta una sfida peculiare, specialmente negli ambienti mediterranei, dove i fenomeni di abbandono e ricolonizzazione naturale stanno minacciando in modo sempre più crescente la capacità delle foreste di fornire benefici alle comunità locali. In queste condizioni, il sistema di governance forestale è chiamato a bilanciare gli impatti del cambiamento dell’uso del suolo con l’assicurazione della salute e della stabilità degli ecosistemi forestali, al fine di garantire la sostenibilità a lungo termine degli ambienti, soprattutto di quelli marginali. Questo lavoro si propone di analizzare in modo più approfondito gli impatti del cambiamento dell’uso del suolo sugli ecosistemi forestali negli ambienti montani italiani. In primo luogo, esegue un’analisi bibliografica dei concetti legati al cambiamento dell’uso del suolo e all’approvvigionamento dei servizi ecosistemici, dalla scala globale a quella locale. In seguito, indaga le relazioni fra le potenzialità adattive di gestione e pianificazione forestali e il cambiamento dell’uso del suolo. Infine, vengono proposte alcune strategie future di possibili strumenti di governance adattiva per affrontare i cambiamenti dell’uso del suolo. Questa infatti può migliorare la resilienza degli ecosistemi forestali riducendo il gap nel campo della ricerca tra il contesto nazionale e quello globale, utilizzando strumenti di valutazione e monitoraggio per simulare cambiamenti e disturbi esterni, e adottando strategie e misure politiche coerenti a scala locale. Land use change is one of the most important drivers for the reduction of ecosystem resilience, and the loss ofbiodiversity and services provision. This is a peculiar challenge, especially in Mediterranean mountain environments,where abandonment and forest transition phenomena increasingly threaten the forest capacity to provide benefits for local communities. Under these conditions, forest governance is called to balance the landuse change impacts and the health and stability of forest ecosystems, in order to ensure the long-term sustainabilityof such marginal environments. This paper aims at deeper understanding the impacts of land use change on forest ecosystem on mountain environments in Italy. At first, a downscaled review on the conceptsof land use change and ecosystem services provision is carried out. Then, according to the review results, therelationships between adaptive capacity of forest management and planning, and land use change is deeply described. Finally, future-oriented strategies of adaptive governance to face land use change are proposed. Inthe context of land use change, adaptive governance can improve forest resilience through filling the researchgaps between the national and the global contexts, adopting monitoring and assessment tools to simulate external changes and disturbances, and effectively implement consistent policy measures and strategies at localscale.

To face summer drought and wildfire in Mediterranean-type ecosystems, plants adopt different strategies that involve considerable rearrangements of biomass allocation and physiological activity. This paper analyses morphological and physiological traits in seedlings of three oak species (Quercus ilex, Quercus trojana and Quercus virgiliana) co-occurring under natural conditions. The aim of this study was to evaluate species-specific characteristics and the response of these oak seedlings to drought stress and fire treatment. Seedlings were kept in a growth chamber that mimicked natural environmental conditions. All three species showed a good degree of tolerance to drought and fire treatments. Differences in specific biomass allocation patterns and physiological traits resulted in phenotypic differences between species. In Q. ilex, drought tolerance depended upon adjustment of the allocation pattern. Q. trojana seedlings undergoing mild to severe drought presented a higher photosystem II (PSII) efficiency than control seedlings. Moreover, Q. trojana showed a very large root system, which corresponded to higher soil area exploitation, and bigger leaf midrib vascular bundles than the other two species. Morphological and physiological performances indicated Q. trojana as the most tolerant to drought and fire. These characteristics contribute to a high recruitment potential of Q. trojana seedlings, which might be the reason for the dominance of this species under natural conditions. Drought increase as a result of climate change is expected to favour Q. trojana, leading to an increase in its spatial distribution.

The synergistic activity between plants and microorganisms may contribute to the implementation of proactive management strategies in the stabilization of contaminated sites, although heavy metals, such as cadmium (Cd), are potentially toxic to them. The aim of this study was to evaluate the degree of tolerance to Cd contamination (supplying twice 40 mg kg(-1) of Cd) in poplar cuttings [clone I-214, P. × euramericana (Dode) Guinier] inoculated or not with two concentrations of Serratia marcescens strain (1 × 10(7) CFU/g and 2 × 10(7) CFU/g of potting mix). The response of the plant-bacteria system to excess Cd was investigated with special reference to the structural traits of plants and the functional efficiency of bacteria. Bacterial colonization and substrate components were previously assessed in order to define the best solution for formulating the experimental plant growth media. The tested plant-bacteria association, especially when bacteria were provided in double concentration, stimulated specific tolerance mechanisms to Cd through the promotion of the poplar growth. Inoculated plants produced larger leaves and increased stem diameter, while roots grew longer and wider in Cd-treated plants. The effect of bacterial inoculum on plant growth traits and metal partitioning in plant organs was assessed in order to define the potential of this poplar clone to be a suitable candidate for phytostabilization of Cd-contaminated soil. The final effect of the inoculation with bacteria, which alleviated the metal load and Cd phytotoxicity due to their bioaccumulation ability, suggests promising phytostabilization potential of these plant-bacteria associations.

L’allocazione del C verso le strutture ipogee delle piante e uno dei principali flussi di C negli ecosistemi terrestri, sebbene ancora non ben quantificato. RAICH e NADELHOFFER (1989), dopo il riesame della letteratura su numerosi ecosistemi forestali, hanno suggerito che l’allocazione ipogea totale di C puo essere stimata dalla differenza fra tassi annuali di respirazione del suolo e caduta di lettiera epigea. DAVIDSON et al. (2002) hanno esteso le analisi dei dati pubblicati confermando le conclusioni di RAICH e NADELHOFFER per foreste mature, sebbene, come osservato da GOWER et al. (1996), l’uso di modelli per la stima del C totale allocato alle radici e per la costruzione di bilanci del C di un soprassuolo non era considerato un metodo valido per la misura dei flussi di C del suolo. Nel presente lavoro di revisione della letteratura abbiamo analizzato nuove misure di respirazione del suolo e di caduta di lettiera, includendo nell’analisi a scala globale sia foreste mature sia formazioni giovani. I risultati ottenuti concordano, in genere, con i lavori precedenti, affermando che la produzione epigea ed ipogea e controllata dagli stessi fattori. Attraverso un gradiente di C da lettiera oscillante fra 52 a 530 g m-2 anno-1, l’allocazione totale ipogea di C aumenta da circa 90 a 1800 g m-2 anno-1. Il rapporto fra allocazione totale ipogea di C e caduta di lettiera diminuisce approssimativamente da 12 a 2.5, con incrementi di C da lettiera da 50 a 200 g m-2 anno-1, ma varia poco quando il C da lettiera aumenta 200 a 500 g m-2 anno-1. Un’analisi di regressione applicata ai dati derivanti da foreste di tutto il mondo ha prodotto la seguente relazione: respirazione annuale del suolo = 140 + 3.09 × caduta annuale di lettiera. La pendenza della regressione indica che, in media, la respirazione del suolo e grossolanamente il triplo del C di lettiera epigea, implicando che l’allocazione ipogea totale di C rappresenta circa il doppio del C di lettiera epigea caduta annualmente. La regressione per i dati provenienti dalle formazioni giovani e piu ripida, rispetto a quanto osservato per le foreste mature, indicando un’eventuale proporzionalmente maggiore allocazione ipogea totale di C, ma l’assunzione dello stato stazionario e piu problematica per le foreste giovani. In effetti, queste deduzioni sono basate su ipotesi incerte sulla stabilita della scorta di C nel suolo. Tuttavia, le variazioni del C del suolo dovrebbero essere molto ampie per modificare la conclusione the l’allocazione ipogea totale di C e generalmente molto maggiore della caduta di lettiera. Queste relazioni permettono la realizzazione di semplici bilanci del C che possono essere usati per porre dei limiti sulla stima della produzione di radici fini in ecosistemi forestali. La determinazione dei tassi di respirazione radicale (radici vive) in ecosistemi forestali puo ulteriormente restringere il raggio di possibili tassi di produzione delle radici, e controllare le ipotesi che l’allocazione totale di C alle radici aumenta con la produzione primaria netta del soprassuolo e che il rapporto fra allocazione totale di C alle radici e produzione primaria netta del soprassuolo diminuisce lungo gradienti globali di disponibilita di risorse. La relazione statistica universale, derivata usando bilanci forestali del C, dovrebbe essere valutata a scala minore, per identificare come variano i modelli d’allocazione del C nelle foreste in funzione dell’eta del bosco, della composizione specifica, e delle pratiche di gestione.

ADDITIONAL INDEX WORDS. CO2 assimilation, carbon balance, leaf area, Olea europaea, shoot growth, sink-source transition ABSTRACT. Net photosynthesis, dark respiration, chlorophyll and carbohydrate content, and leaf and shoot growth in plants of evergreen olive (Olea europaea L.) grown under controlled conditions were measured to assess changes in carbon balance during leaf development of the 6th, 12th, and 16th node (from the base, first flush) through expansion to maturity. Shoot and leaves expanded in a sigmoid pattern with differences among nodes. Photosynthesis varied with leaf development; 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 exceeds the daily increase in leaf carbohydrate content, occurred before full leaf expansion, between 10% and 30% expansion depending on the node. Leaves are the main source of CO2 assimilation in plants. The growth of developing leaves initially depends on imported resources (Turgeon and Webb, 1975). Photosynthetic rates are generally low in young expanding leaves and increase up to or slightly after full leaf area expansion; as carbohydrates accumulate, import stops and the export of soluble sugars begins. In early phases of leaf growth, the leaf is a net carbon importer (sink), its growth depending mainly on a supply of imported substances; afterwards it becomes a net carbon exporter (source), its growth depending primarily on its photosynthates. This stage of leaf development may take several days or weeks; leaves of dicotyledonous plants change from sink to source when their area reaches 30% to 60% of the final area (Turgeon, 1989). The capacity of a tissue to import carbohydrates is a measure of its sink strength (Kozlowski, 1992). The position and distribution of leaves along the shoot influences sink strength. The direction of translocation of assimilates varies with the developmental stage of single leaves; fully developed apical leaves export carbohydrates towards younger leaves, basal leaves send carbohydrates to the shoot and roots, intermediate leaves in both directions (Dickson and Isebrand, 1991). Because large amounts of carbohydrates are used in respiration by sinks, absolute growth rate or rate of accumulation of dry matter does not accurately measure the capacity of a sink to receive assimilates. A more appropriate index of actual sink strength is the sum of net carbon gain and respiratory carbon loss. During early stages of leaf growth, syn- thesis of chlorophyll, proteins and structural compounds is high, resulting in high catabolic rates to support energy need. As the photosynthetic system matures, the requirement for respiratory energy rapidly decreases (Kozlowski, 1992).

SUMMARY Two poplar clones, hybrid Populus deltoides Bartr. Ex Marsh X Populus nigra L. (Populus xeuramericana), clone I-214, and Populus deltoides, clone Lux, were grown from hardwood cuttings for one growing season in either ambient (360 μmol mol−1) or elevated (560 μmol mol−1) [CO2] in FACE-systemrings at Rapolano Terme (Siena, Italy). Both clones I-214 and Lux exhibited a higher aboveground bio-mass, photosynthesis at light saturation and instantaneous transpiration efficiency (ITE) in CO2-enriched air. The elevated [CO2]-induced responses of clone I-214 included increased investment in branch and leaf biomass, and enhanced stem volume. The elevated [CO2]-induced responses of clone Lux included an increase in the number of branches (and foliage area). Indication of photosynthetic acclimation under elevated [CO2] was found during the early morning, but only in clone I-214. Stomatal conductance decreased under elevated [CO2] particularly in clone Lux. Clone differences in response to elevated [CO2] shoul...

SUMMARY Plants of Vitis vinifera (cv. Sangiovese) were submitted to elevated carbon dioxide concentrations in the field, using a FACE array; the experiment took place in a vineyard in Central Italy, throughout two growth seasons. The effects of fumigation on productivity, product quality and plant water relations were evaluated. Both vegetative growth and yield were increased, while no differences were evidenced in plant phenology. A significant decrease in stomatal conductance did not result in marked differences in leaf water potential, while osmotic adjustment induced by elevated CO2 in leaves was evident at the final stage of the growing season, but such an observation was year dependent.

A field experiment on olive trees (Olea europaea L.) was designed with the objective to search for an optimum irrigation scheduling by analyzing the possible effects of deficit irrigation. Treatments were: a non-irrigated control (rainfed) and three treatments that received seasonal water amount equivalent to 33 and 66% of crop evapotranspiration (ETC) in the period August–September (respectively 33II and 66II), and 66% of (ETC) from late May to early October (66I-II). Atmospheric evaporative demand and soil moisture conditions were regularly monitored. Irrigation effects on plant water relations were characterized throughout a growing season. Whole-plant water use, in deficit irrigated (66I-II) and rainfed olive trees, was determined using a xylem sap flow method (compensation heat-pulse technique). The magnitude of variations in water use and the seasonal dynamic of water relations varied among treatments, suggesting that olive trees were strongly responsive to both irrigation amount and time. Physiological parameters responded to variations in tree water status, soil moisture conditions and atmospheric evaporative demand. All measurements of tree water status were highly correlated with one another. There was a considerable degree of agreement between daily transpiration deduced from heat-pulse velocity and that determined by calibration using the water balance technique. Deficit irrigation during the whole summer (66I-II) resulted in improved plant water relations with respect to other watering regimes; while, severe regulated deficit irrigation differentiated only slightly 33II treatment from rainfed plants. Nevertheless, regulated deficit irrigation of olive trees after pit hardening (66II) could be recommended, at least in soil, cultivar and environmental conditions of this study.

In this study, the effects of non-hazardous levels of heavy metal (Zn, Cu, Cr and Cd)-enriched organic waste on biomass partitioning and heavy metal accumulation in plant organs in July and October were determined for two poplar clones (Populus deltoides × maximowiczii—clone Eridano and P. × euramericana—clone I-214) commonly used in Italian poplar plantations. Soil amended with the industrial organic waste did not exert any toxic effects on plants. Leaf, stem, root and woody cutting biomasses of treated plants were significantly greater than in the controls in both clones, except for stem biomass at the beginning of October. Leaf area of Eridano and I-124 treated plants was significantly higher than that of control plants, both in July and October, while specific leaf area (SLA) did not show any significant changes due to treatment. Shoot (SMR) and root mass ratios (RMR) were not significantly affected by the treatment in July, while in October plants grown in treated soil showed significant differences in stem and root biomass allocation with respect to controls. Among the four heavy metals (Zn, Cu, Cr and Cd) contained in the industrial organic waste, only Zn, Cu and Cr concentrations in plants differed consistently between clones or soil treatments, while Cd levels were always below the detection limits. Both phytoextraction and phytostabilisation strategies were observed in the two clones studied. The results suggested that only non-hazardous industrial biosolid levels might be environmentally sustainable for poplar plantations. © 2004 Elsevier B.V. All rights reserved.

Seasonal changes in foliage nitrogen (N) and carbon (C) concentrations and δ15N and δ13C ratios were monitored during a year in Erica arborea, Myrtus communis and Juniperus communis co-occurring at a natural CO2 spring (elevated [CO2], about 700 μmol mol−1) and at a nearby control site (ambient [CO2], 360 μmol mol−1) in a Mediterranean environment. Leaf N concentration was lower in elevated [CO2] than in ambient [CO2] for M. communis, higher for J. communis, and dependent on the season for E. arborea. Leaf C concentration was negatively affected by atmospheric CO2 enrichment, regardless of the species. C/N ratio varied concomitantly to N. Leaves in elevated [CO2] showed lower δ13C, and therefore likely lower water use efficiencies than leaves at the control site, regardless of the species, suggesting substantial photosynthetic acclimation under long-term CO2-enriched atmosphere. Leaves of E. arborea showed lower values of δ15N under elevated [CO2], but this was not the case of M. communis and J. communis foliage. The use of the resources and leaf chemical composition are affected by elevated [CO2], but such an effect varies during the year, and is species-dependent. The seasonal dependency and species specificity suggest that plants are able to exploit different available water and N resources within Mediterranean sites.

Summary •W e hypothesized that poplar can be useful for the extraction of zinc (Zn) from contaminated soils and water. However, the physiological response and the base of tolerance of poplar plants to this heavy metal are little known. • Plants of Populus deltoides × P . nigra ( P. × euramericana ) I-214 clone were grown in glasshouse and treated with three different Zn concentrations (1, 100 and 1000 µ M ). Growth analysis, Zn concentration in leaves, stem and roots, and photosynthetic parameters were measured at different times of exposure during the annual growth cycle. • Significant reductions in foliage and total dry mass, and impairment of gas exchange properties occurred at applications of 100 µ M and 1000 µ M Zn. Modifications of leaf area, chlorophyll b concentration, diameter at the stem base, and Zn concentrations of old leaves, stem and roots were also shown after Zn treatment. •W e concluded that poplar plants have the potential to be used for plantations in Zn-contaminated soils, in the range of tested Zn concentrations.

Five-year-old olive plants (cvs. Frantoio and Moraiolo) grown in large pots were exposed for seven months to ambient or high atmospheric CO2 concentration ([CO2]) in free-air CO2 enrichment facility. Exposure to elevated [CO2] enhanced net photosynthesis and decreased stomatal conductance, leading to greater water use efficiency. Stomatal density also decreased in elevated [CO2], while the ratio of intercellular to atmospheric [CO2] did not differ among leaves grown in ambient or enriched [CO2]. Cultivar differences in response to high [CO2] should be taken into account when planning future olive plantations in forecasted warmer and drier Mediterranean sites.

The current work deals with the use in a Mediterranean environment of a simulation model of forest ecosystem processes which was originally created for temperate areas (FOREST-BGC). The model was calibrated and applied on two deciduous forest stands in Tuscany (Central Italy) by using conventional and remote sensing data as inputs. First, information on the two stands needed to initialise the model was derived from different sources, while meteorological data were extrapolated from a nearby station by an existing procedure (MT-Clim). Temporal profiles of leaf area index (LAI) were then derived both from direct ground measurement and from the processing of NOAA-AVHRR NDVI data. The model was calibrated using stand transpiration values obtained for 1997 by a sap flow method. Next, its performances were tested against the same transpiration values measured in 1998. The results obtained indicate that FOREST-BGC is capable of simulating water fluxes of Mediterranean forests when suitable LAI profiles are considered. Moreover, the derivation of these profiles from NDVI data can improve the model performance probably due to an enhanced consideration of the effects of the typical Mediterranean summer water stress. These results support the final objective of the work, which is the development of a procedure capable of integrating conventional and remote sensing data to operationally simulate water and carbon fluxes on a regional scale.

Predictions of shifts in rainfall patterns as atmospheric [CO 2 ] increases could impact the growth of fast growing trees such as Populus spp. and Salix spp. and the interaction between elevated CO 2 and water stress in these species is unknown. The objectives of this study were to characterize the responses to elevated CO 2 and water stress in these two species, and to determine if elevated CO 2 mitigated drought stress effects. Gas exchange, water potential components, whole plant transpiration and growth response to soil drying and recovery were assessed in hybrid poplar (clone 53-246) and willow (Salix sagitta) rooted cuttings growing in either ambient (350 pmol mol -1 ) or elevated (700 pmol mol -1 ) atmospheric CO 2 concentration ([CO 2 ]). Predawn water potential decreased with increasing water stress while midday water potentials remained unchanged (isohydric response). Turgor potentials at both predawn and midday increased in elevated [CO 2 ], indicative of osmotic adjustment. Gas exchange was reduced by water stress while elevated [CO 2 ] increased photosynthetic rates, reduced leaf conductance and nearly doubled instantaneous transpiration efficiency in both species. Dark respiration decreased in elevated [CO 2 ] and water stress reduced Rd in the trees growing in ambient [CO 2 ]. Willow had 56% lower whole plant hydraulic conductivity than poplar, and showed a 14% increase in elevated [CO 2 ] while poplar was unresponsive. The physiological responses exhibited by poplar and willow to elevated [CO 2 ] and water stress, singly, suggest that these species respond like other tree species. The interaction of [CO 2 ] and water stress suggests that elevated [CO 2 ] did mitigate the effects of water stress in willow, but not in poplar.

SummaryThis field experiment was carried out to investigate the physiological changes following water stress in bell pepper plants and their consequences on fruit yield. Bell pepper plants were grown under irrigated and rainfed conditions. Water availability to plants was assessed by measurements of leaf water potentials. Growth was determined by measuring plant (above-ground) and fruit dry-mass accumulation. Solar radiation intercepted by the crop was measured with a linear net radiometer. Leaf protein content and ion accumulation in leaves and fruits were biochemically determined. Leaf photosynthesis and stomatal conductance were measured and mesophyll conductance was estimated in vivo during the crop cycle under field conditions using a portable gas analyser. The quantum yields of the two photosystems were estimated by measurements of chlorophyll fluorescence and absorbance (at 830 nm), in rapid succession. Dry-mass accumulation in above-ground plant organs, gas-exchange characteristics, leaf water pot...

One-year-old olive (Olea europaea L) cuttings of two cultivars (Frantoio and Moraiolo) were exposed for five months to ambient (360 ± 16 μmol mol-1) or elevated (560 ± 52 μmol mol-1) CO2 concentration in a free-air CO2 enrichment facility. Current-year leaves were used for gas exchange measurements, chlorophyll and nutrient determinations. Stomatal density was measured on frozen hydrated current-year leaves by low temperature scanning electron microscopy. Above-ground dry mass (stem and leaves) and leaf area were determined, and leaf mass ratio and specific leaf area calculated. Results showed that exposure to elevated CO2 enhanced rates of net photosynthesis and decreased stomatal conductance, leading to higher water use efficiency; this was not translated in increased growth rates (particularly in the cultivar Frantoio, which showed reductions in above-ground plant dry mass compared with the cultivar Moraiolo). Chlorophyll concentrations (chlorophyll content per unit leaf area) decreased only i...

On Mt. Etna (Italy), an enhanced Normalized Difference in Vegetation Index (NDVI) signature was detected in the summers of 2001 and 2002 along a distinct line where, in November 2002, a flank eruption subsequently occurred. These observations suggest that pre-eruptive volcanic activity may have enhanced photosynthesis along the future eruptive fissure. If a direct relation between NDVI and future volcanic eruptions could be established, it would provide a straightforward and low-cost method for early detection of upcoming eruptions. However, it is unclear if, or to what extent, the observed enhancement of NDVI can be attributed to volcanic activity prior to the subsequent eruption. We consequently aimed at determining whether an increase in ambient temperature or additional water availability owing to the rise of magma and degassing of water vapour prior to the eruption could have increased photosynthesis of Mt. Etna's trees. Using dendro-climatic analyses we quantified the sensitivity of tree ring widths to temperature and precipitation at high elevation stands on Mt. Etna. Our findings suggest that tree growth at high elevation on Mt. Etna is weakly influenced by climate, and that neither an increase in water availability nor an increase in temperature induced by pre-eruptive activity is a plausible mechanism for enhanced photosynthesis before the 2002/2003 flank eruption. Our findings thus imply that other, yet unknown, factors must be sought as causes of the pre-eruption enhancement of NDVI on Mt. Etna. ISSN:1932-6203

Soil cadmium (Cd) contamination is becoming a matter of great global concern. The identification of plants differentially sensitive to Cd excess is of interest for the selection of genotype adaptive to grow and develop in polluted areas and capable of ameliorating or reducing the negative environmental effects of this toxic metal. The two poplar clones I-214 (Populus × canadensis) and Eridano (Populus deltoides × maximowiczii) are, respectively, tolerant and sensitive to ozone (O3) exposure. Because stress tolerance is mediated by an array of overlapping defence mechanisms, we tested the hypothesis that these two clones differently sensitive to O3 stress factor also exhibit different tolerance to Cd. With this purpose, an outdoor pot experiment was designed to study the responses of I-214 and Eridano to the distribution of different Cd solutions enriched with CdCl2 (0, 50 and 150 μM) for 35 days. Changes in leaf area, biomass allocation and Cd uptake, photosynthesis, chlorophyll fluorescence, leaf concentration of nutrients and pigments, hydrogen peroxide (H2O2) and nitric oxide (NO) production and thiol compounds were investigated. The two poplar clones showed similar sensitivity to excess Cd in terms of biomass production, photosynthesis activity and Cd accumulation, though physiological and biochemical traits revealed different defence strategies. In particular, Eridano maintained in any Cd treatment the number of its constitutively wider blade leaves, while the number of I-214 leaves (with lower size) was reduced. H2O2 increased 4.5- and 13-fold in I-214 leaves after the lowest (L) and highest (H) Cd treatments, respectively, revealing the induction of oxidative burst. NO, constitutively higher in I-214 than Eridano, progressively increased in both clones with the enhancement of Cd concentration in the substrate. I-214 showed a more elevated antioxidative capacity (GSH/GSSG) and higher photochemical efficiency of PSII (Fv/Fm) and de-epoxidation degree of xantophylls-cycle (DEPS). The glutathione pool was not affected by Cd treatment in both clones, while non-protein thiols and phytochelatins were reduced at L Cd treatment in I-214. Overall, these two clones presented high adaptability to Cd stress and are both suitable to develop and growth in environments contaminated with this metal, thus being promising for their potential use in phytoremediation programmes.

Information on plant responses to combined stresses such as ozone (O3) and cadmium (Cd) is scarce in tree species. On the other hand, high O3 concentrations in the atmosphere and heavy metal contaminations in water and soil simultaneously affect forest ecosystems. Toxic metals may exacerbate the consequences of air pollutants. In this research, two poplar clones, differently sensitive to O3 ("I-214" O3-tolerant and "Eridano" O3-sensitive), were grown for 5 weeks in pots supplied with 0 and 150 mg Cd kg(-1) soil and then exposed to a 15-day O3 fumigation (60 nl l(-1), 5 h a day) or supplied with charcoal-filtered air under the same conditions (referred to as control samples). The effects of the two stressors, alone or in combination, on Cd accumulation, photosynthetic capacity, ethylene emission and oxidative state were investigated in fully expanded leaves. Cadmium accumulation in leaves caused a reduction, but not complete failure, of photosynthesis in Eridano and I-214 poplar clones. The reduction in assimilation rate was more important following O3 fumigation. Stomatal aperture after O3 treatment, instead, increased in I-214 and decreased in Eridano. Overall, Cd treatment was effective in decreasing ethylene emission, whereas O3 fumigation increased it in both clones, although interacting with the metal treatment. Again, O3 fumigation induced a significant increase in ascorbate (ASA) + dehydroascorbate (DHA) content, which was strongly oxidised by O3, thus decreasing the redox state. On the other hand, Cd treatment had a positive effect on ASA content and redox state in I-214, but not in Eridano. Although Cd and O3 are known to share some common toxicity pathways, the combined effects induced distinct clone-specific responses, underlying the complexity of plant reactions to multiple stresses.

Changes in intrinsic water use efficiency (iWUE) were investigated in Fagus sylvatica and Nothofagus spp. over the last century. We combined dendrochronological methods with dual-isotope analysis to investigate whether atmospheric changes enhanced iWUE of Fagus and Nothofagus and tree growth (basal area increment, BAI) along latitudinal gradients in Italy and Chile. Post-maturation phases of the trees presented different patterns in δ13C, Δ13C, δ18O, Ci (internal CO2 concentration), iWUE, and BAI. A continuous enhancement in isotope-derived iWUE was observed throughout the twentieth century, which was common to all sites and related to changes in Ca (ambient CO2 concentration) and secondarily to increases in temperature. In contrast to other studies, we observed a general increasing trend of BAI, with the exception of F. sylvatica in Aspromonte. Both iWUE and BAI were uncoupled with the estimated drought index, which is in agreement with the absence of enduring decline in tree growth. In general, δ13C and δ18O showed a weak relationship, suggesting the major influence of photosynthetic rate on Ci and δ13C, and the minor contribution of the regulation of stomatal conductance to iWUE. The substantial warming observed during the twentieth century did not result in a clear pattern of increased drought stress along these latitudinal transects, because of the variability in temporal trends of precipitation and in specific responses of populations.

Recent investigations have highlighted the dependence of Mediterranean forest production on spring rainfall. The current work introduces the concept of the start of the dry season (SDS) and performs a three-step analysis to determine the effect of SDS on Mediterranean forest production. Seven forest zones of Tuscany (Central Italy), which present differently pronounced Mediterranean features, are considered. First, a statistical analysis investigates the influence of spring water budget on forest Normalized Difference Vegetation Index (NDVI) inter-annual variations during July–August. The analysis is then extended to assess the impact of inter-annual SDS variability on forest gross primary production (GPP) simulated by a NDVI driven parametric model, modified C-Fix. These simulations lead to rank the considered forest types according to the relevance of SDS in regulating inter-annual GPP variations. The application of similar statistical analyses to detrended tree ring-width time series of typical Tuscany forests confirms the existence of an eco-climatic gradient in the functional relevance of SDS. The influence of SDS on tree growth is attenuated moving from Mediterranean arid to temperate humid environments. These findings are examined and interpreted from an eco-physiological viewpoint taking into consideration the peculiarity of Mediterranean forest ecosystems. Next, relevant implications are discussed in view of the possible consequences of ongoing climate change.

Questions:Could mountainpine (Pinus mugo Turra subsp. mugo) located abovethe timberline and at the southern limit of its potential geographic distributionbea promising speciestomonitorclimatic changeinspecificenvironmentssuchas the Mediterranean mountains? Does mountain pine krummholz upwardexpansion result from current climate change? Has the relationship betweenclimate and tree ring growth of mountain pine changed? To what extent doesclimatic variability affect tree ring growth? Could mountain pine upwardexpansion contribute to loss of biodiversity in the undisturbed tree line ecotoneon the Majella massif?Location:MajellaNationalPark,Apennines,Italy.Methods: Dendroclimatological analysis was performed to examine the rela-tionshipbetweentreeringsofmountainpineandclimaticparametersatthetreeline. Climate–growth relationships were analysed using correlation function(CF)analysisandmovingCF(MCF).Results: In the Majella massif, climate variables affected mountain pine treegrowth at the tree line ecotone. Significant correlations were found with springtemperatures and summer precipitation. Essentially, 3 mo played a key role inmountain pine growth: April and May of the current year and October of theprevious year. MCF showed that mountain pine is a sensitive species, in termsoftreeringgrowth.Conclusions: Growing above the limit of tree vegetation, mountain pineproved to be a promising species for monitoring climate- and land use-driveninfluences over tree ring growth at high elevations. Our results show thatmountain pine is particularly sensitive to climate at the beginning and at theendofthegrowingseason.IntroductionIn the central Apennines (Italy), the low altitudinal rangeand marked influence of mediterranean climate set theboundary between alpine and sub-alpine bioclimatic beltsat 2550 m a.s.l. Within the Mediterranean Basin, theApennine range represents a temperate mountain climatic‘island’withinwhichthecentralApenninesformanarchi-pelago of arctic-alpine ‘islands’ (van Gils et al. 2012). TheApennine chain acted as refugia for trees during theW€urmian Late Glacial (Watson 1996), playing an impor-tant role in preservation of endemic high-altitude vegeta

presents original and review papers of the International Symposium ‘WSE: Wood Structure in Plant Biology and Ecology’, held in Naples on 17–20 April 2013 and organized by the Department of Agricultural and Food Sciences of the University of Naples Federico II and the Department of Environmental, Biological and Pharmaceutical Sciences and Technologies of the Second University of Naples on behalf of the COST Action FP 1106 STReESS, ‘

Drought acclimation is attained by avoidance mechanisms in the short term and by adaptation changes in the long term. In this study, we applied deficit irrigation at nursery stage to elicit species-specific physiological responses and biomass production in two ornamental shrub species, comparing two settings: open air (OA) and greenhouse (GH). Viburnum opulus L. and Photinia x fraseri 'Red robin' were compared under three irrigation levels: severe water deficit (SWD), moderate water deficit (MWD) and control (C). In both experiments, SWD induced lower values of water potentials in both species whereas MWD had similar effects to C. In OA, SWD reduced earlier stomatal conductance in V. opulus and photosynthesis rate in P. x fraseri and in GH V. opulus showed a reduction of gas exchange even in MWD. P. x fraseri showed greater stomatal control capacity. In contrast, treatments did not affect PSII efficiency even if P. x fraseri proved a greater capacity to differentiate the I-P phase of the fluorescence transient in SWD conditions. In both experiments, SWD and MWD affected leaf area by lowering the number of leaves in P. x fraseri and reducing leaf surface in V. opulus. Moreover, V. opulus showed early leaf senescence and premature fall. Deficit irrigation had effects also on leaf characteristics: smaller leaf area unit in V. opulus, reduced biomass and leaf mass per area and succulence in both species, increase of spongy tissue thickness. Eventually, we can state that P. x fraseri can withstand 30 % evapotranspiration, while maintaining functionality.,Key message: This study shows that deficit irrigation can be encouraged in productive activities like plant nursing, especially with the most resistant species.

Recent papers have demonstrated the applicability of a calibrated bio-geochemical model – BIOME-BGC - for estimating current annual increments (CAIs) of Mediterranean forests. In this study, the above model is applied to assess the gross primary production (GPP) of nine beech forest sites in Italy using a previously produced data set of meteorological data over a ten-year period (1999- 2008). The obtained GPP estimates are integrated with relevant autotrophic respiration and allocation to obtain forest net primary production (NPP) averages for the same forests. The simulations are performed assuming different levels of ecosystem disequilibrium, i.e., progressively taking into account the effects of specific site history in terms of woody biomass removal and stand aging. The NPP estimates, converted into CAIs by means of specific coefficients, are validated through comparison with data derived from tree growth measurements. Results indicate that the modeling of quasi-equilibrium conditions tends to produce overestimated CAI values, particularly for not fully stocked, old stands. The inclusion of information on existing biomass leads to a partial improvement, while optimal results are obtained when information on ecosystem development phase is considered. The implications of using different NPP estimation methods are finally discussed in the perspective of assessing the forest carbon budget on a national basis. L'articolo è disponibile sul sito dell'editore http://www.sisef.it/

Leaf mineral concentrations of co-occurring Erica arborea, Juniperus communis and Myrtus communis were measured at bimonthly intervals throughout a year in a natural CO2 spring and in a nearby control site with similar soil chemistry in a Mediterranean environment. There were different responses to the elevated [CO2] (c. 700 m LL ‐1 ) of the spring site plants depending on the element and the species. In the CO2 spring site K, Ca, Mg, Mn, Al, Fe, and Ti leaf concentrations and the ratio C/N showed significant greater values in at least one or two of the three species. Leaf S concentration were greater in all three species. Leaf concentrations of N, Sr, Co, and B were lower in at least one or two species, and those of C and Ba were lower in all the three studied species near the CO2 spring. P, Na, Zn, Si, Cu, Ni, Cr, Pb, Mo, V and Cd leaf concentrations and the specific leaf area (SLA, measured in Myrtus communis) did not show any consistent or significant pattern in response to the elevated [CO2 ]o f the spring site. There was a slight trend towards maximum concentrations of most of these elements during autumn‐winter and minimum values during the spring season, especially in Myrtus communis. Multivariate principal component analyses based on the leaf elemental concentrations clearly differentiated the two sites and the three species. Lower concentrations at the spring site were not the result of a dilution effect by increased structural or nonstructural carbon. In contrast to most experimental studies of CO2 enrichment, mainly conducted for short periods, several of these elements had greater concentrations in the CO2 spring site. Nutrient acclimation and possible causes including decreased nutrient export, increased nutrient uptake capacity, photosynthetic down-regulation, Mediterranean water stress, and higher H2S concentration in the spring site are discussed.

Seasonal changes in tissue water relations of Erica arborea L., Myrtus communis L. and Juniperus communis L., grown in a Mediterranean environment, were analysed under field conditions over a 12 month period 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. Tissue water relations varied in response to changes in water availability, but the seasonal course of tissue water relations parameters was also related to ontogeny. Tissue water relations of these co-occurring shrubs were not alike. Osmotic potentials and saturated mass/dry mass ratio were lowest during peak drought stress periods. Diurnal changes in osmotic potential at the point of turgor loss were least early in the season, maximal in mid-season, and decreased again in autumn. Turgor potentials decreased as drought progressed and were highest in late fall and mid-winter. Symplastic water fraction was highest in mid-spring for E. arborea and M. communis and decreased during the summer, while the opposite was observed for J. communis. Common to all species, under elevated [CO2], was an increase of turgor pressure, particularly during the summer months. Other parameters showed species-specific responses to long-term elevated [CO2]. In particular, exposure to elevated [CO2] increased osmotic potentials in E. arborea under drought, while the opposite was the case for J. communis. Site differences in predawn to midday shifts were not strong in any of the species. Differences in tissue water relations suggest that the coexistence of these shrubs in the same environment with similar water availability are partially based on differential water relations strategies and water use patterns. Regardless of the mechanisms, growth of these shrubs in elevated [CO2] may be either less, similarly or more affected by drought stress than plants in ambient [CO2] depending on the species and season.

The geographic variation in monoterpene composition, growth, and carbon isotope discrimination (Δ) was assessed for trees of maritime pine, Pinus pinaster Ait., from five provenances (one Portuguese, Corsican, and Tuscan and two Sardinian: Telti and Limbara) grown on four different field sites in Sardinia island, Italy. Analysis of monoterpenes as biochemical markers revealed differentiation among the provenances and suggest four groupings, corresponding to the pooled Sardinian provenances (Telti and Limbara) and the other individually separated provenances. The five provenances exhibited statistically significant variation for height and diameter. Significant variation for growth parameters were also observed among the locations studied. The five provenances showed weak variations for Δ (range 17.1-17.5‰), while highly significant differences were observed amongst the four sites. A strong negative correlation was observed between mean tree height and mean Δ for the five provenances only at one site (the coolest and highest); the relationship was weak for the five seed sources at the other three locations. The Portuguese provenance that showed the highest potential for growth amongst the seed sources studied had a distinct terpene pattern and a tendency for lower Δ (higher WUE) than the other populations.

Ring widths of five Mediterranean forest tree species (Arbutus unedo, Fraxinus ornus, Quercus cerris, Quercus ilex and Quercus pubescens) growing close to a natural source of CO2 in Tuscany, Italy and at a nearby control site were compared. At the CO2-enriched site, trees have been growing for decades under elevated CO2 concentrations. They originated from parent trees that also grew under elevated CO2 in natural conditions, and they have been continuously exposed to elevated CO2 throughout their growth. Tree-ring series from each of the species were prepared. Assigning calendar dates to rings was difficult but possible, and ring-width series were built for all species. The ring-width data were analysed using a two-sided t-test to assess if there was a difference between the radial growth at the CO2-enriched site and the control site. The cumulative basal area at the same cambial age at both sites was also compared using a Wilcoxon test. Radial growth of trees at the CO2-enriched site was not significantly different from growth at the control site. For each species, year by year, radial growth at the CO2-enriched site was tested against the control site and significant differences were found in only a few years; these differences were not synchronous with extreme climatic events. The expected increase in above-ground productivity, as one of the ecosystem responses to increasing CO2 during drought stress, was not observed in this Mediterranean woody plant community, despite being water-limited. Other resource limitations, such as low nutrient availability (common in the Mediterranean region), may have counteracted the positive effect of elevated CO2 under drought stress, or trees may have acclimated to the high CO2.

Photosynthetic parameters were studied in Arbutus unedo L. trees growing at either ambient (AC) or elevated EC (mean 465 µmol mol-1) CO2 concentration near a natural CO2 vent in Orciatico, Italy Diurnal courses of net photosynthetic rate (P N), ratio of variable to maximum chlorophyll fluorescence (Fv/Fm), and quantum yield of electron transport through photosystem 2 (Φ2) were measured on sun and shade leaves. The contents of N, C, Ca, K, P, and chlorophyll (Chl) and specific leaf area (SLA) in these leaf categories were also determined. A morning peak and midday depression of P N were found for both AC and EC sun leaves. Long-term EC caused little or no down-acclimation of P N in sum leaves. The estimate of total daily CO2 uptake was lower in AC leaves than in EC leaves. In shade leaves, it reached up to 70 % of the value of sun leaves. The Fv/Fm ratio showed decreasing trend in the morning, reached a minimum at midday (90 % of dawn value), and then increased in the afternoon. The EC had no effect on Fv/Fm either in sun or shade leaves. Plants grown near the CO2 spring had lower Chl content, higher SLA, and higher Ca and K contents than plants grown under AC.

Des semis de Quercus virginiana Mill. ont ete exposes pendant six mois a deux concentrations en CO 2 atmospherique (370 μmol mol -1 ou 520 μmol mol -1 ) en combinaison avec deux traitements d'alimentation en azote (20 et 90 μmol mol -1 N total) du sol dans des chambres a ciel ouvert. Des semis ont ete recoltes a intervalle de 5-7 semaines. Le traitement CO 2 a eu un effet positif sur la croissance des semis. Les differences observees dans le poids de la biomasse entre les deux traitements CO 2 ont augmente au cours de la periode d'experimentation. La disponibilite du sol en azote n'a pas affecte la croissance de maniere significative. Neanmoins, la croissance en CO 2 elevee, en combinaison avec des niveaux eleves d'azote, amene une accumulation uniformement plus elevee de biomasse totale en fin d'experience (30-40 %). L'allocation de biomasse entre les differentes parties a ete semblable dans tous les traitements, mais etait sensiblement differente entre les recoltes. Les regimes azotes n'ont pas entraine de difference dans les taux de croissance relative (RGR) et les taux d'assimilation nette (NAR), alors que le traitement de CO 2 avait un effet significatif. A travers toutes les concentrations en CO 2 et les niveaux d'apport azote, il a ete mis en evidence une relation positive entre la masse des plantes et RGR, et cette relation n'a pas differe entre les traitements. La surface specifique de feuille (SLA) a diminue en concentration elevee de CO 2 . Le rapport de la masse de racine fine et de la masse de feuillage a ete augmente en forte concentration en CO 2 et a diminue avec les fortes concentrations en azote. Les semis traites avec une forte concentration en azote en CO 2 ont eu la plus grande croissance en hauteur et en diametre. Les rapports allometriques entre la biomasse de tige et de la racine et entre la croissance en hauteur et en diametre n'ont pas ete sensiblement affectes par une concentration elevee. Les concentrations du feuillage en azote ont ete reduites par les basses concentrations en azote du sol. La concentration en azote des semis diminue avec le temps. La concentration elevee en CO 2 a augmente le rapport C/N de tous les compartiments des semis, en raison de la diminution des concentrations en azote. Les semis soumis a une concentration elevee en CO 2 ont reduit les concentrations en azote comparativement au traitement CO 2 en concentration actuelle, si la comparaison se fait sur une base temporelle, mais sont semblables si l'on compare des semis de hauteurs identiques.

We determined the direct effects of atmospheric CO, concentration ((CO,)) on leaf gas exchange, phenolic and carbohy- drate allocation in live oak seedlings (Quercus virginiana Mill.) grown at present (370 μmol·molor elevated (520 μmol·mol (CO,) for 6 months in open-top chambers. Two soil nitrogen (N) treatments (20 and 90 μmol·mol total N, low N and high N treat- ments, respectively) were imposed by watering the plants every 5 d with modified water soluble fertilizer. Enhanced rates of leaf- level photosynthesis were maintained in plants subjected to elevated (COover the 6-month treatment period in both N treatments. A combination of increased rates of photosynthesis and decreased stomatal conductance was responsible for nearly doubling water use efficiency under elevated (COThe sustained increase in photosynthetic rate was accompanied by decreased dark respiration in elevated (COElevated (CO led to increased growth rates, while total non-structural carbohydrate (sugars and starch) concentra- tions were not significantly affected by elevated (CO,) treatment. The concentration of phenolic compounds increased significantly under elevated (CO,). (© Inra/Elsevier, Paris.)

Des jeunes plants de Quercus ilex L., issus d'une population d'arbres ayant pousse dans une concentration elevee de CO 2 , ont ete exposes a deux concentrations en CO 2 (370 μmol mol -1 ou 520 μmol mol -1 ) en combinaison avec deux fertilisations du sol en azote (20 et 90 μmol mol -1 N total) dans des chambres a ciel ouvert pendant six mois. L'augmentation de concentration en CO 2 stimule la photosynthese et la respiration nocturne des feuilles independamment du traitement en azote. Les augmentations de photosynthese et de la respiration nocturne des feuilles ont ete associees a une reduction moderee de conductance stomatique, ayant pour resultat d'augmenter l'efficience transpiratoire instantanee des feuilles des jeunes plants cultives en CO 2 eleve. L'augmentation de concentration du CO 2 accroit la production de biomasse seulement dans le traitement eleve en azote. Le rapport des racines fines a la masse de feuillage a diminue avec le traitement en azote et a augmente avec l'enrichissement en CO 2 . La surface specifique de feuille (SLA) et les taux de la surface de feuille (LAR) ont diminue de maniere significative pour les feuilles des jeunes plants developpes sous une concentration elevee de CO 2 , independamment du traitement en azote. La concentration en azote des feuilles a diminue de maniere significative dans le traitement eleve en CO 2 , independamment du traitement en azote. En raison des configurations des concentrations d'azote et de carbone, le taux C/N a augmente avec le traitement eleve en CO 2 et diminue avec l'apport d'azote. Dans l'apres-midi, les concentrations en amidon des feuilles n'ont pas augmente de maniere significative avec l'augmentation du CO 2 , comme pour les concentrations en amidon dans le cas du traitement limite en azote du matin. Les concentrations en amidon dans les feuilles, la tige et les racines ont augmente dans le cas du traitement avec une concentration elevee en CO 2 et diminue avec l'apport en azote. Les concentrations en sucre n'ont pas ete affectees sensiblement par les traitements de CO 2 ou de N. Les concentrations phenoliques foliaires totales ont diminue pour les jeunes plants qui ont pousse dans le traitement en O 2 eleve, independamment du traitement en N. Nous concluons que la disponibilite en azote dans le sol jouera un role majeur dans l'etablissement et la croissance de Q. ilex dans un environnement caracterise par un accroissement de la concentration en CO 2 dans l'air.

The transpiration of a mature beech (Fagus sylvatica L.) forest was measured over a whole season by the heat pulse velocity technique and the results analysed in terms of a new analytical canopy conductance model, which takes into account the effects of partial decoupling from the atmosphere on the local humidity environment experienced by the canopy. Stand daily transpiration ranged from 0·62 to 2·97 mm d–1, with a seasonal mean value of 1·97 mm d–1. Maximum canopy conductance was 18·5 mm s–1, with a mean estimated value of 5·0 mm s–1; computed values were little affected by the assumption of neutral atmospheric conditions. The decoupling coefficient Ω varied greatly on a daily and seasonal basis, with an average value of 0·28. As a result of partial decoupling, the estimated vapour pressure deficit at the notional canopy surface exceeded the values measured above the canopy by 380 Pa on average. When correctly expressed in terms of humidity at the canopy surface, the model explained 80% of the variance in half-hourly transpiration measurements. Upon cross-validation it still explained 72% of the variance, as compared to only 40% when correction for partial decoupling was not introduced. A baseline canopy conductance of 0·7 mm s–1, not modulated by the environment, was estimated. The implications of the model are discussed for the representation of canopy conductance and transpiration of broad-leaf forests.