Leaf photosynthetic traits of 14 tropical rain forest species in relation to leaf nitrogen concentration and shade tolerance

Variability of leaf traits related to photosynthesis was assessed in seedlings from 14 tree species growing in the tropical rain forest of French Guiana. Leaf photosynthetic capacity (maximum rate of carboxylation and maximum rate of electron transport) was estimated by fitting a biochemical model of photosynthesis to response curves of net CO2 assimilation rate versus intercellular CO2 mole fraction. Leaf morphology described by leaf mass per unit leaf area (LMA), density and thickness, as well as area- and mass-based nitrogen (N) and carbon (C) concentrations, were recorded on the same leaves. Large interspecific variability was detected in photosynthetic capacity as well as in leaf structure and leaf N and C concentrations. No correlation was found between leaf thickness and density. The correlations between area- and mass-based leaf N concentration and photosynthetic capacity were poor. Conversely, the species differed greatly in relative N allocation to carboxylation and bioenergetics. Principal component analysis (PCA) revealed that, of the recorded traits, only the computed fraction of total leaf N invested in photosynthesis was tightly correlated to photosynthetic capacity. We also used PCA to test to what extent species with similar shade tolerances displayed converging leaf traits related to photosynthesis. No clear-cut ranking could be detected among the shade-tolerant groups, as confirmed by a one-way ANOVA. We conclude that the large interspecific diversity in photosynthetic capacity was mostly explained by differences in the relative allocation of N to photosynthesis and not by leaf N concentration, and that leaf traits related to photosynthetic capacity did not discriminate shade-tolerance ranking of these tropical tree species.     

Diversity of leaf traits related to productivity in 31 Populus deltoides x Populus nigra clones

To test if some leaf parameters are predictors of productivity in a range of Populus deltoides (Bartr.) Marsh. x P. nigra L. clones, we assessed leaf traits and productivity in 2-month-old rooted cuttings from 31 clones growing in 4-l pots in a greenhouse, under conditions of controlled temperature and optimal irrigation. We evaluated four groups of variables describing (1) productivity (total biomass), (2) leaf growth (total leaf number increment and total leaf area increment rate), (3) leaf structure (specific leaf area and nitrogen and carbon contents) and (4) carbon isotope discrimination (delta), which is negatively correlated with time-integrated water-use efficiency. High-yielding clones did not necessarily display high leaf growth rates, but they displayed a larger total leaf area, lower specific leaf area and lower leaf nitrogen concentration than clones with low productivity. Total leaf area was mainly controlled by maximal individual leaf area and total leaf area increment rate (r = 0.51 and 0.56, respectively). Carbon isotope discrimination did not correlate with total biomass, but it was associated with total number of leaves and total leaf area increment rate (r = 0.39 and 0.45, respectively). Therefore, leaf area and specific leaf area were better indicators of productivity than leaf growth traits. The observed independence of delta from biomass production provides opportunities for selecting poplar clones combining high productivity and high water-use efficiency.     

Paclobutrazol affects the resistance of black spruce to high light and thermal stress

Detached needles from 20-week-old black spruce (Picea mariana (Mill.) B.S.P.) seedlings root-drenched with 60 mg of paclobutrazol were exposed to two temperatures (22 and 50 degrees C) and two light treatments (100 and 1900 &mgr;mol m(-2) s(-1) PAR) in a factorial combination for 4 h in vitro. Mean dry weights of individual needles from paclobutrazol-treated plants were approximately 1.9 times heavier than that of needles from untreated controls at 22 degrees C, but no differences were observed following incubation at 50 degrees C. Numbers of cells per needle remained constant in all treatments. Chlorophyll and carotenoid contents per needle were higher in seedlings treated with paclobutrazol than in untreated control seedlings, and the differences were most pronounced in the high temperature plus high light treatment. In low light at 50 degrees C, quantum efficiency of photosystem II was 45% higher in needles of paclobutrazol-treated seedlings than in needles of untreated control seedlings, but quantum efficiency of needles from treated seedlings declined when needles were exposed to high light at either temperature. Peroxidase and superoxide dismutase activities were up-regulated by paclobutrazol, whereas catalase activities were depressed and no significant differences were observed between treated and control needles at 50 degrees C in either light treatment. Paclobutrazol treatment did not moderate the depressive effects of high temperature on total soluble protein or on the activity of ribulose-1,5-bisphosphate carboxylase. In contrast, high activities of phosphoenolpyruvate carboxylase were maintained in paclobutrazol-treated needles under all stress conditions, whereas large losses in activity were recorded in untreated needles at 50 degrees C. Collectively, these observations suggest that paclobutrazol treatment may convey resistance to excessive light and high temperatures by increasing the potential of conifers to limit damage caused by oxidative stress.     

Zur Synchronisation der Entwicklung vonEpiblema tedella Cl. (Lep. Tortricidae) und ihres ParasitenLissonota dubia Hgn. (Hym. Ichneumonidae)

Zusammenfassung Lissonota dubia verbringt als biophager Endoparasit neun Monate in der Leibeshöhle der Larve seines WirtsEpiblema tedella. Die Larvenentwicklung von Wirt und Parasit verläuft nicht synchron, da während der vier bis fünf Monate währenden Winterruhe die Wirtslarve sich schon im Vorpuppenstadium, der Parasit dagegen erst im 2. Larvenstadium befindet. Die Weiterentwicklung zur Vollwüchsigkeit vollzieht dieLissonota-Larve nach der Überwinterung sehr schnell, so daß die Parasitimagines nur etwa drei Wochen später erscheinen als die Wirtsimagines.Die erwachsenenEpiblema-Larven treten im Herbst in Diapause, die jedoch offensichtlich schon im Februar in einen Quieszenz-Zustand übergeht. Im Gegensatz dazu begibt sich ein großer Teil derLissonota-Larven im Herbst nicht in Diapause, sondern nur in Quieszenz, und kann deshalb jederzeit unter geeigneten Temperaturbedingungen die Entwicklung fortsetzen. Ein anderer Teil derLissonota-Larven weist allem Anschein nach im Herbst eine festere Arretierung der Entwicklung auf und verhält sich ähnlich wieEpiblema. Diese physiologische Heterogenität derLissonota-Population könnte als eine zusätzliche Sicherung der zeitlichen Koinzidenz angesehen werden, da sie eine weitere Streuung der imaginalen Schlüpfzeiten zur Folge haben kann. Ein solcher Sachverhalt muß fürLissonota von Vorteil sein, zumal die zeitliche Koinzidenz der Parasitenweibchen mit dam 1.Wirtslarvenstadium nicht durch einen hormonalen Synchronisationsmechanismus, sondern nur durch die Temperatur der Bodenstreu gesteuert zu werden scheint.

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Summary Lissonota dubia Hgn., a biophagous endoparasite ofEpiblema (= Epinotia) tedella Cl., stays for nine months in the body cavity of its host larva. The development of the larvae of host and parasite do not proceed simultanously, since theLissonota larva is still in the second stage, when the host larva has reached the prepupal instar at the time it enters the litter for hibernation (Fig. 1). Although after hibernation the development of host and parasite stars from very different instars, the adult ofLissonota appears only three weeks after theEpiblema moth.Under laboratory conditions the interval between the emergence of the host and the parasite depends on the duration of natural hibernation temperatures before laboratory treatment. If suitable feeding conditions are given continuously during autumn to the fullgrown host larvae, the larvae ofLissonota partly develop to adults without any diapause, while the development of the host is blocked, except for some specimens, which emerge some time afterLissonota (Fig. 2 Tab. 1 and 2). As Figure 3 demonstrates, the posthibernation development ofLissonota is not accelerated after cold treatment by temporary exposure to low hibernation temperatures, but inEpiblema a dependence is evident.From these results it can be concluded that the fullgrown host larvae have a diapause, which seems to change into a quiescence state in February. A great number ofLissonota larvea (orLissonota hosts) stay only in quiescence and are able to continue the development at any time, when suitable temperatures occur. The otherLissonota larvea seem to be retarded in their further development during the first weeks of the hibernation period and therefore to react similar toEpiblema.This physiological heterogeneity of theLissonota population could provide additional security to the temporal coincidence, because it can prolong the emergence period of the parasite. It must be a useful principle, since the temporal coincidence for the parasitization ofEpiblema byLissonota is not controlled by a hormonal mechanism — as it seemed earlier, but mainly (perhaps only) by the soil temperatures in spring.

     

Darstellungen des Teufels und der abtrünnigen Engel in Insektengestalt

Summary Interpretation of the devil and of apostatized angles as insect.The origin of the interpretation of angles as insects must be sought in the sumeric and Babylonic cultures. At that time men thought that air-ghosts can transform themselves into insects. Up to 12th century the Devil was pictured in form of man. Than under the influence of Christian Church the holy animals of the Teutons, insects inclusive, were transformed into embodiment of the Evil One (the Devil).

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A-1040 Wien IV, Wiedner Hauptstr. 45–47, III/23.     

Strahlungseinflüsse und „Biophysikalische Effekte”

Ohne ZusammenfassungHerrn Professor Dr. G. BECKER zum 60. Geburtstag gewidmet     

Rundschau

Ohne Zusammenfassung     

Parameterization and testing of a biochemically based photosynthesis model for walnut (Juglans regia) trees and seedlings

The biochemically based leaf photosynthesis model proposed by Farquhar et al. (1980) and the stomatal conductance model proposed by Jarvis (1976) were parameterized for walnut. Responses of photosynthesis to CO(2) and irradiance were used to determine the key parameters of the photosynthesis model. Concurrently, stomatal conductance responses to leaf irradiance (Q), leaf temperature (T(l)), water vapor pressure deficit at the leaf surface (D), and air CO(2) concentration at the leaf surface (C(s)) were used to parameterize the stomatal conductance model. To test the generality of the model parameters, measurements were made on leaves from a 20-year-old tree growing in the field, and from sunlit and shaded greenhouse-grown seedlings. The three key parameters of the photosynthesis model (maximum carboxylation rate V(cmax), electron transport capacity J(max), and dark respiration rate R(d)) and the key parameter of the conductance model (reference stomatal conductance, g(sref)) were linearly correlated with the amount of leaf nitrogen per unit leaf area. Unique relationships could be used to describe nitrogen effects on these parameters for leaves from both the tree and the seedlings. Our data allowed separation of the effects of increasing total photosynthetic apparatus per unit leaf area from the effects of partitioning nitrogen among different pools of this apparatus for foliage acclimation to leaf irradiance. Strong correlations were found between stomatal conductance g(s) and Q, D and C(s), whereas the relationship between g(s) and T(l) was weak. Based on these parameterizations, the model adequately predicted leaf photosynthesis and stomatal conductance when tested with an independent set of data obtained for the tree and seedlings. Total light-driven electron flows derived from chlorophyll fluorescence data obtained at different leaf temperatures were consistent with values computed by the model. The model was also tested with branch bag data acquired from a three-year-old potted walnut tree. Despite a relatively large variance between observed and simulated values, the model predicted stomatal conductance and photosynthesis reasonably well at the branch scale. The results indicate that the photosynthesis-conductance model developed here is robust and can be applied to walnut trees and seedlings under various environmental conditions where water is non-limiting.     

Das Käferkreuz bei Klosterneuburg

Ohne Zusammenfassung