The activity and number of protocerebral neurosecretory neurons of the dorsolateral group (L1, L2 and L2'), as well as the size of the corpora allata were investigated in 5th instar larvae of the gypsy moth (Lymantria dispar) from two populations (oak and locust-tree forests) fed one of two host-plants (oak is a suitable and locust-tree an unsuitable host-plant).
The monitoring of activity related cytological parameters and the number of protocerebral dorsolateral neurosecretory neurons revealed that differently adapted populations respond to nutritive stress differently. The activity of the L1 neurosecretory neurons in the protocerebra of the caterpillars is low in those from the locust-tree forest regardless of host-plant quality. The L2 neurosecretory neurons in the oak population become active when they were fed the unsuitable host-plant whereas their activity was high in locust-tree caterpillars regardless of the host-plant. A decrease in the number of neurosecretory neurons in a response to a novel food was noticed in both populations. The activity of the L2' neurosecretory neurons was similar in all caterpillars, but their number was increased in those from the locust-tree forest. The corpora allata of the locust-tree caterpillars were large whereas those of the oak forest caterpillars only increased in size when they were fed locust-tree leaves.
It is obvious that nutritive stress results in neurosecretory reorganization and changes in the titre of hormones that modulate the morphogenetic programme.
Carpathian forests represent unique and well-preserved ecosystems in relatively intensively managed forests of Europe. Habitat use, foraging assemblages and activity patterns of a bat community were investigated in semi-natural beech-oak forest by monitoring echolocation calls and mist-netting at three localities during the summers of 2003 and 2004. Six different forest habitat types were studied: oak forest, beech forest, stream, road, forest edge and open area within the forest. Bats were detected in all habitats. Sixteen species were found. Habitats were used differently by the individual species. The highest species diversity was observed in the forest interior. The first peak of flight activity was after sunset which then declined and was relatively even through the night until the second peak before sunrise, which was recorded in the forest interior, open area and on the road. The highest flight activity was recorded at the forest edge, forest stream and in open area. Recorded activity was 3× lower in the oak forest interior compared to the forest edge, but if the extent of the forests is considered, forest interior is the most important foraging habitat. Consequently future forest management should consider the needs of this endangered group of animals.
The aphid Tuberculatus quercicola (Matsumura), a non host-alternating species, lives on Daimyo oak, Quercus dentata Thumberg, and other species of oak. In summer there was a significant reduction in the total amino acid concentration in phloem sap of the host plant and fecundity of the aphids. There are two phenotypes of Q. dentata: one produces flush leaves in mid-July and the other does not. This study investigates the effect of the flush leaves produced by Q. dentata in summer on the density, fecundity and honeydew excretion by T. quercicola. Of 20 shoots on each of the study trees, 6-13 (average 8.8 shoots) produced secondary shoots with flush leaves. The number of aphids on flush leaves sharply increased by two-fold compared to that on mature leaves. The aphids reared on flush leaves were significantly larger and had a larger embryo number compared to those on mature leaves. These results suggest that the phloem sap of flush leaves has a high nutritive quality for aphids. However, in mid-summer and early autumn T. quercicola went into reproductive diapause regardless of whether it was reared on flush or mature leaves. Aphid colonies persisted until October even on trees that did not produce secondary leaves. These observations suggest that this aphid does not depend on secondary leaf production. Thus, the use of flush leaves does not enable T. quercicola to avoid nutritional stress in summer and the need for reproductive diapause.
Five-year-old trees of deciduous Quercus robur L., evergreen Q. ilex L., and their semideciduous hybrid, Q. × turneri Willd. (var. pseudoturneri), growing in pots, were subjected to drought stress by withholding water for 18-22 days, until leaf water potentials decreased below -2 MPa. Gas-exchange rates, oxygen evolution, and modulated chlorophyll (Chl) fluorescence measurements revealed that by strong stomata closure and declining photosynthetic capacity down to approximately 50%, all three taxa responded with strongly reduced photosynthesis rates. In Q. robur, photochemical quenching of the drought-stressed plants was much lower than in nonstressed controls. Dissection of the occurring events in the photosynthetic electron transport chain by fast Chl fluorescence induction analysis with the JIP-test were discussed. and S. Koller, V. Holland, W. Brüggemann.
In search for new forestation tree species for future Central European climate conditions, Mediterranean evergreen oak taxa are investigated for their summer drought- and winter frost-hardiness. Here we report on the winter performance of the photosynthetic apparatus of Quercus × hispanica Lam. and its evergreen parental species Q. suber L. under extraordinary harsh winter conditions. Both taxa showed a strong decline of photosystem II (PSII) quantum efficiency (Fv/Fm) with a concomitant increase in the deepoxidation state (DES) of the xanthophyll pigments depending on (severe) frost events during winter, and these parameters significantly correlated with minimum air temperatures during periods of chronic photoinhibition at mid-winter, but not at the onset of winter in response to the first frost nights. Fv/Fm and DES correlated with each other in both taxa throughout the winter. and V. Holland, W. Brüggemann.
Quercus ilex plants grown on two different substrates, sand soil (C) and compost (CG), were exposed to photosynthetic photon flux densities (PPFD) at 390 and 800 µmol(CO2) mol-1 (C390 and C800). At C800 both C and CG plants showed a significant increase of net photosynthetic rate (PN) and electron transport rate (ETR) in response to PPFD increase as compared to C390. In addition, at C800 lower non-photochemical quenching (NPQ) values were observed. The differences between C390 and C800 were related to PPFD. The higher PN and ETR and the lower dissipative processes found in CG plants at both CO2 concentrations as compared to C plants suggest that substrate influences significantly photosynthetic response of Q. ilex plants. Moreover, short-term exposures at elevated CO2 decreased nitrate photo-assimilation in leaves independently from substrate of growth. and C. Arena, L. Vitale, A. Virzo De Santo.
The relationship between chlorophyll (Chl) content and net photosynthetic rate (PN) in an isolated Quercus ilex tree, growing inside Villa Pamphili Park in Rome, was explored. The highest PN was in March, May, and September (10.1 μmol m-2 s-1, maximum rate). PN decreased by 65 % (with respect to the yearly maximum) when leaf temperature reached 34 °C, and by 50 % when leaf temperature was 9 °C. The highest Chl contents were in April, October [1.47 g kg-1 (d.m.), maximum value], and December. The lowest Chl content was found in July (0.78 g kg-1). The decrease of PN in July was in close connection with the decrease of Chl content. On the contrary, the high Chl content during winter did not correspond with PN of this season. Discordances between Chl content and PN over the year influenced the regression analysis, which although positive did not show very high correlation coefficients (r = 0.7). The high Chl (a+b) content during most of the year indicated that the photosynthetic apparatus remained basically intact also during stress periods. and L. Gratani, P. Pesoli, M. F. Crescente.
Despite their wide distribution and frequent occurrence, the spatial distribution patterns of the well-known gall-inducing insects Mikiola fagi (Hartig) and Neuroterus quercusbaccarum (L.) in the canopies of mature trees are poorly described. We made use of the Swiss Canopy Crane (SCC) near Basel, Switzerland, to gain access to the canopy of a mixed temperate forest up to a height of 35 m. Within one and a half days we scanned 6,750 beech leaves and 6,000 oak leaves. M.fagi showed a distinct vertical zonation with highest abundance in the top-most parts of the canopy as well as a significant aggregation on particular trees. N. quercusbaccarum showed an even more pronounced preference for particular trees and a general preference for Quercus robur over Q. petraea. In contrast to M. fagi, no vertical zonation could be detected. We think that both gall-inducing species have greater powers of dispersal than formerly assumed since they overwinter on the forest floor and yet are able to 1) gain access to the entire canopy, 2) show preference for certain host trees. We found little evidence for the phenological synchrony hypothesis proposed to explain the intertree distribution of N. quercusbaccarum. The highest density of M. fagi galls was in those parts of the canopy exposed to high solar radiation; their host choice is probably determined by micro-climatological factors. The consequences of the distribution patterns of N. quercusbaccarum and M. fagi for their ecological interactions with the host-plant, inquilines and parasitoids (e.g., canopy-layer specific performance linked to plant chemistry, density-dependent parasitism) need now to be subjected to further scientific investigation.