The photosynthetic pigments and photochemical efficiency of photosystem 2 (PS2) were studied in four constitutive species (Achillea millefolium L., Festuca pseudovina Hack. ex Wiesb., Potentilla arenaria Borkh., and Thymus degenianus Lyka) of a semiarid grassland in South-eastern Hungary. Every species displayed typical sun-adapted traits and substantial plasticity in the composition and functioning of the photosynthetic apparatus. The contents of chlorophylls (Chls) and carotenoids (Cars) on a dry matter basis declined from May to July, however, the amount of total Cars on a Chl basis increased. This increase was the largest in Potentilla (48 %) and the smallest in Achillea (14 %). The pool of xanthophylls (VAZ) was between 25 % and 45 % of the total Car content and was larger in July than in May. The content of β-carotene increased by July, but lutein content did not change significantly. The Chl fluorescence ratio Fv/Fm was reduced by 3-10 % at noon, reflecting the down-regulation of PS2 in the period of high irradiance and high temperature. The occurrence of minimal values of ΔF/Fm' showed close correlation to the de-epoxidation rate of violaxanthin. Hence in natural habitats these species developed a considerable capacity to dissipate excess excitation energy in the summer period in their photosynthetic apparatus through the xanthophyll cycle pool and a related photoprotective mechanism, when the photochemical utilization of photon energy was down-regulated. and S. Veres ... [et al.]
We investigated seasonal patterns of photosynthetic responses to CO2 concentrations in Spartina alterniflora Loisel, an aerenchymous halophyte grass, from a salt marsh of the Bay of Fundy (NB, Canada), and from plants grown from rhizome in controlled-environment chambers. From late May to August, CO2 compensation concentrations (Γ) of field-grown leaves varied between 2.5-10.7 cm3(CO2) m-3, with a mean of 5.4 cm3(CO2) m-3. From September onwards field leaves showed CO2 compensation concentrations from 6.6-21.1 cm3(CO2) m-3, with a mean of 13.1 cm3 m-3 well into the C3-C4 intermediate range. The seasonal variability in Γ did not result from changing respiration, but rather from a sigmoidal response of net photosynthetic rate (PN) to applied CO2 concentration, found in all tested leaves but which became more pronounced late in the season. One explanation for the sigmoidal response of PN to external CO2 concentration could be internal delivery of CO2 from roots and rhizomes to bundle sheath cells via the aerenchyma, but the sigmoidal responses in S. alterniflora persisted out to the tips of leaves, while the aerenchyma extend only to mid-leaf. The sigmoidicity persisted when CO2 response curves were measured from low to high CO2, or from high to low CO2, and even when prolonged acclimation times were used at each CO2 concentration. and M. O. Bärlocher ... [et al.].
The aim of present studies was to examine the interrelationships between reproductive events, age, body mass and steroid hormones in roe deer females (Capreolus capreolus). For this purpose we compared seasonal changes in body mass, blood levels of progesterone and estradiol (1) in young (1 year) and adult (2-4 years old) does and (2) in pregnant and non-pregnant animals. Monthly during 12 months all animals were weighed, blood plasma was collected, and concentration of progesterone and estradiol was analysed by RIA. Pregnant animals had significantly higher body weight, than non-pregnant ones, in November (before foetus implantation), and lower body weight in comparison with non-pregnant females in August (after parturition). In non-pregnant females high level of progesterone was observed from August (mating) up to December. Thereafter progesterone level declined up to minimum in summer months (April-July). Pregnant animals had increased progesterone level from February (foetus implantation) up to June (time after labour). In non-pregnant females, three peaks of estradiol concentration were observed in October, December and May. Pregnant animals, in contrast to non-pregnant females, had spring (January-March) gravidity-associated peak of estradiol level, but absence of summer (May) peak before parturition. Comparison of annual changes in body weight and plasma steroid hormone level in pregnant yearlings and old animals, as well as the number of offspring in these animals did not show principal age-dependent differences in these indexes, although yearlings had higher absolute progesterone (in December) and estradiol (in October and November) level than old animals. Our observations suggest significant seasonal changes in plasma progesterone and estradiol level and body weight in this species. Substantial differences in these changes in pregnant and non-pregnant animals demonstrate the involvement of steroid hormones in control of pregnancy in roe deer does. The absence of age-dependent differences in body weight and fecundity rate do not confirm previous hypothesis that age-dependent differences in metabolism and body mass can reduce fertility rate in yearlings. Moreover, our observations are the first demonstration of higher rate of steroidogenesis in young animals, than in adult females during early stages of gravidity and before embryo implantation. It is not to be excluded, that age-dependent reduction in ovarian steroid hormones level could be a cause of future infertility in old animals.
The mating behaviour of Pyrrhocoris apterus in the laboratory is well studied, but little is known about it under natural conditions. In natural populations in Central Europe, overwintered adults start copulating in March and continue until their death. Caged females, kept under natural conditions in the permanent presence of males, copulated repeatedly. Their mating activity increased sharply until early April, then very slowly until the end of June and then declined as the females die-off. Half of copulations were short (< 5 h) and only 9% were longer than 1 day. By contrast, in natural populations, mating activity (percentage of individuals involved in copula) reached its maximum in April and then decreased until early July, when the overwintered adults die. The decline in mating frequency (percentage of adults involved in copula) was associated with a decrease in the availability of receptive females towards the end of the mating period. For a female, repeated copulation is necessary because sperm is nearly depleted after insemination of 3-5 egg batches.
Spring and summer composition and species richness of bruchid pre-dispersal seed predator assemblages associated with species of leguminous plants were monitored in a four-year non-experimental survey of 32 service areas along five highways in Hungary. The vegetation bands along highways (delimited by fences) were considered a special type of ecotone where herbaceous plants are exposed to regular mowing and therefore the composition of the vegetation there is very different from the adjacent vegetation. Altogether 57 herbaceous and woody species of leguminous plants were recorded at these sites, harbouring 20 autochthonous, 3 allochthonous, but established, and 4 recently introduced species of bruchid seed predators (Coleoptera: Chrysomelidae: Bruchinae). The species of leguminous plants recorded along highway verges during this project make up approximately one fourth of the Fabaceae in Hungary and of the bruchids ca. 80 % (!) of the species known to occur in Hungary. At half of the service areas, mowing decreased the species richness of leguminous plants compared to that recorded prior to mowing, but not that of their bruchid seed predators. However, the species composition of the bruchid assemblages before and after mowing changed substantially. Null-model analyses indicated a random organization of spring assemblages and a deterministic one of summer assemblages of bruchids; very likely a result of host-specificity constraints. Calculations of host specificity confirmed the narrow host range recorded for bruchids that emerged from the samples of plants, in spite of new host records, such as three and two Trifolium species for Bruchidius picipes and Bi. sp. prope varius sensu Anton, respectively, Oxytropis pilosa for Bi. marginalis and Vicia cracca for Bruchus brachialis. Our results show that a surprisingly high number of species of bruchids occur in highway margins, however, the management of the vegetation there prevents a substantial portion of the native bruchid fauna establishing permanent populations.
The seasonal changes of photosynthesis of cones of Japanese larch (Larix kaempferi Carr.) trees showed that gross photosynthetic rate of young cones (G) was 2-3 µmol m-2 s-1 at surface area unit and PG / RD (dark respiration of cones) peaked about 0.7 in the same period, indicating that 70 % of respiratory CO2 was re-fixed. With maturation, PG and PG / RD sharply decreased. Chlorophyll content in cones was 3-20 % of that in leaves, which made it a limiting factor for photosynthesis and its content was closely correlated with photosynthetic capacity. Although sunken and linearly arranged stomatal organs were found on the scale of young cones, differently from the significant regulation of leaf photosynthesis, these stomata tended to be non-functional since CO2 is not limiting factor for cone photosynthesis. Thus photosynthesis of larch cones is an additional contribution to their development. and W.-J. Wang ... [et al.].