Environmental control of CO2 assimilation rates and stomatal conductance in five oak species growing under field conditions in Greece

The present study compared CO2 assimilation rate and stomatal conductance of five oak species from the beginning of May through November 1993 under similar natural conditions. Gas exchange, leaf characteristics and water status were measured on 30-year-old Quercus ilex, Q macrolepis, Q pedunculiflora, Q pubescens and Q trojana growing in experimental plots in northern Greece. The seasonal pattern of assimilation rates was similar for all study species but differences occurred between the species. After initial leaf expansion, all species rapidly developed high photosynthetic rates. In addition, assimilation rates were high in all species in May and November after rain events. No significant differences in stomatal conductance were observed among species during the growing season. The relationships between assimilation rate and stomatal conductance displayed variation in the slopes among species and months.Effets de l'environnement sur l'assimilation nette de CO2 et la conductance stomatique de cinq espèces de chênes en plantation en Grèce. Cette étude a permis la comparaison des niveaux d'assimilation nette de CO2 et de conductance stomatique de cinq espèces de chênes en plantation comparative dans le nord de la Grèce, au cours d'une saison de végétation (mai-novembre 1993). Les échanges gazeux, les caractéristiques foliaires et l'état hydrique ont été déterminés sur des arbres de 30 ans de Quercus ilex, Q macrolepis, Q pedunculiflora, Q pubescens et Q trojana. La dynamique saisonnière d'assimilation nette était très semblable entre espèces. Des différences significatives sont apparues à certains moments. Après la phase d'expansion initiale des feuilles, toutes les espèces présentaient de fortes valeurs d'assimilation, de même que pendant les périodes pluvieuses en mai et en novembre. Peu de différences interspécifiques de conductance stomatiques ont été détectées au cours de la saison. Cependant, les relations entre conductance stomatique et assimilation nette ont fortement différé suivant les espèces et les périodes de mesure

Rose productivity and physiological responses to different substrates for soil-less culture

Cultivation of roses in various soil-less media was studied with the aim to identify the optimum soil condition for rose production. Madelon roses grafted on rootstock of Rosa indica var. major were transplanted to polyethylene bags containing zeolite and perlite (at ratios of 25z:75p, 50z:50p, 75z:25p and 100z:0p, v/v) in a climate-controlled greenhouse. Net photosynthesis (Anet), stomatal conductance (gs) and water use efficiency (WUE) of roses were followed for 5 months. Flower production and quality were recorded in three flowering flushes during a 5-month period. Analysis of variance of repeated measurements showed that even though the overall Anet did not differ among treatments (average 18.7 μmol m−2 s−1), trends in Anet seasonality for roses in 25z:75p substrate differed significantly from those in 50z:50p, 75z:25p or 100z:0p. Stomatal conductance did not show any significant seasonality or trends in response to substrate mixtures, averaging 0.89 mol m−2 s−1. Water use efficiency was significantly lower for roses in 25z:75p than in 100z:0p mixtures (1.8 ± 0.15 and 2.0 ± 0.13 μmol m−2 s−1 CO2 /mmol m−2 s−1 H2 O, respectively). Cumulative production of rose plants did not differ among substrate mixtures. Productivity significantly differed among flower stem classes. Stem class I (\u3e70 cm) and class V (≤30 cm) exhibited the least production, contributing to only 7.6 and 3.7% of the total production, respectively. The highest productivity was observed in classes III (51–60 cm) and IV (31–50 cm), contributing to the bulk of productivity (68.4%). Class II contributed a 20.3% of the production. Results showed that zeolite and perlite acted as inert materials. Zeolite did not exert any positive effect on productivity, in contrast to what has been reported in literature recently. Use of perlite resulted in a little improvement in photosynthesis, however this improvement was not reflected by a significant increase in production