No abstract

Effects of changing light conditions on the ecophysiological condition behind survival were examined on beech from two different populations. Plants were grown in a greenhouse under simulated understorey and canopy gap light conditions. Upon exposure to high light maximum photosynthesis of shade-acclimated leaves increased followed by a reduction over several days to between high- and low-light control rates. In the reciprocal transfer, the decrease in maximum photosynthesis was rapid during the first 2–3 days and then levelled off to values comparable to low-light controls. Seedlings from Sicily (Madonie) showed generally higher maximum photosynthetic rates than those from Abetone. Leaf conductance varied in the same direction as photosynthesis in high- to low-light seedlings but to a lesser degree. Leaves grown under low light and exposed to high light experienced photoinhibition. The Abetone population was more susceptible to photoinhibitory damage than the seedlings from Sicily. Exposure to high light of shade-acclimated seedlings resulted in intermediate chlorophyll concentrations between levels of the high-light and low-light seedlings. Carotenoid concentration was unaffected by treatments. Seedlings grew more in high light, but had a lower leaf area ratio. Light-limited seedlings showed a shift in carbon allocation to foliage. Leaves formed in the new light regime maintained the same anatomy that had been developed before transfer. Seedlings from Sicily had thicker leaves than those of seedlings from Abetone. Seedlings from Abetone were found to be more susceptible to changing light conditions than seedlings from Sicily. We conclude that small forest gaps may represent a favorable environment for photosynthesis and growth of beech regeneration as a result of the limited ability of seedlings to acclimate to sudden increases in high irradiance and because of the moderate levels of light stress in small gaps

In a 0.75-ha plot in a Norway spruce (Picea abies Karst.) -silver fir (Abies alba Miller) stand in Comelico (Italian eastern Alps), we analysed (i) the distribution and growth of natural regeneration of Norway spruce and silver fir as affected by stand structure and (ii) the age structure of all saplings between 0.2 and 10 m in height in a 30-yearold gap. In both species, most natural regeneration was clumped and located at the margin of the gaps; however, fir saplings were more represented in understorey environments and less represented in gaps as compared with spruce. Age structure of natural regeneration in the selected gap revealed that the majority (75%) of saplings appeared after the formation of the gap; however, for regeneration taller than 2 m (which has a better chance of reaching the uppermost canopy layer), saplings already present at gap formation predominated. We conclude that (i) gap edges represent a preferential regeneration niche in this forest and (ii) saplings established before gap formation can play an important role in gap refilling. These results provide useful information to ensure, through silvicultural practices, favourable conditions for the temporal and spatial continuity of the regeneration process.Résumé : Nous avons analysé dans une placette de 0,75 ha située dans un peuplement d'épinette de Norvège (Picea abies Karst.) -sapin argenté (Abies alba (Miller)) de Comelico (dans la partie est des Alpes italiennes) : (i) la distribution et la croissance de la régénération naturelle de l'épinette de Norvège et du sapin argenté telles qu'affectées par la structure du peuplement et (ii) la structure d'âge de toutes les gaules de 0,2 à 10 m de hauteur dans une trouée vieille de 30 ans. Chez les deux espèces, la régénération naturelle était regroupée et localisée à la marge des trouées; toutefois et en comparaison avec l'épinette, les gaules du sapin étaient plus représentées dans des environnements sous couvert et moins représentées dans les trouées. La structure d'âge de la régénération naturelle dans la trouée échantil-lonnée montre que la majorité (75 %) des gaules sont apparues après la formation de la trouée; toutefois, quant à la ré-génération plus haute que 2 m (qui a de meilleures chances de rejoindre la couche la plus haute du couvert), les gaules déjà présentes au moment de la formation de la trouée prédominaient. Nous concluons que : (i) la bordure des trouées représente une niche préférentielle pour la régénération dans cette forêt et que (ii) les gaules établies avant la formation de la trouée peuvent jouer un rôle important dans sa fermeture. Ces résultats fournissent une information utile pour assurer, par le biais de pratiques sylvicoles, des conditions favorables à la continuité spatio-temporelle de la régénération.

Prunus avium trees were grown in sand culture for one vegetative season with contrasting N supplies, in order to precondition their N storage capacities. During the spring of the second year a constant amount of 15 N was supplied to all the trees, and the recovery of unlabelled N in the new biomass production was used as a direct measure of N remobilization. Destructive harvests were taken during spring to determine the pattern of N remobilization and uptake. Measurements of both xylem sap amino acid profiles and whole tree transpiration rates were taken, to determine whether specific amino acids are translocated as a consequence of N remobilization and if remobilization can be quantified by calculating the flux of these amino acids in the xylem. Whereas remobilization started immediately after bud burst, N derived from uptake by root appeared in the leaves only 3 weeks later. The tree internal N status affected both the amount of N remobilization and its dynamics. The concentration of xylem sap amino acids peaked shortly after bud burst, concurrently with the period of fastest remobilization. Few amino acids and amides (Gln, Asn and Asp) were responsible for most of N translocated through the xylem; however, their relative concentration varied over spring, demonstrating that the transport of remobilized N occurred mainly with Gln whereas transport of N taken up from roots occurred mainly with Asn. Coupling measurements of amino acid N in the xylem sap with transpiration values was well correlated with the recovery of unlabelled N in the new biomass production. These results are discussed in relation to the possibility of measuring the spring remobilization of N in field-grown trees by calculating the flux of N translocation in the xylem.

Data collected from 183 poplar and 102 willow SRC experimental plots, located in Central-North Italy, were subjected to stepwise regression analysis to acquire information on the environmental factors affecting plant survival and productivity in the first two-year rotation cycle. Nine Populus ×canadensis Mönch, eight P. deltoids Bartr. clones and four hybrids of Salix matsudana Koidz were included in analysis. Independent variables were: annual and seasonal water availability (rainfall and irrigation), annual mean air temperature, soil texture, pH, N and organic matter content, planting density and management intensity. Dependent variables were: a) mean annual yield during the first two-year rotation cycle in tons per hectare per year of dry matter (Odt·ha ); b) plant survival at the end of the second year from planting (%). Water availability resulted the main variable driving plant survival and biomass production in both poplar and willow clones. Water availability appeared to be the principal factor affecting the establishment of poplar and willow energy plantations in the Po valley. Possible variations in the rainfall regime consequent to climate changes could seriously influence land suitability to SRC. Experimental data also indicate that choice of planting density may increase the biomass yield during the first two-year especially with P. deltoides clones. © Versita Sp. z o.o. Keywords: Biomass production • Poplar • Willow • Short rotation coppice • Soil texture • Climate factors • Soil nutrient contents 1 CRA -Agricultural Research Council, PLF -Research Unit for Wood Production Outside Forests, I-15033 Casale Monferrato (AL), Italy IntroductionBiomass from short rotation coppice (SRC) is one of the possible alternatives to fossil fuels in Europe. Poplar and willow SRC plantations can produce large amounts of dry matter in a relatively short time (e.g. 1-2 years) maintaining their yield capacity throughout many years [1].During the last 5 years about 6000 hectares of energy plantations (Short-Rotation-Coppices, SRC) have been established in Italy, mainly in the Po valley, where biomass thermoelectric power plants are under construction, and the Regional Programs for Rural Development included a series of financial incentives to support the establishment and maintenance of SRC. The planted species were those recommended for the North and Central Italy by the National guidelines for energy plantations [2,3] namely poplars (Populus Cent. Eur.