Net photosynthetic (P^) and transpiration (£) rates and stomatal conductance (gj) were determined in cotton genotypes under drought during the growth cycle. A decrease in P^, E and gs was observed as soil water availability diminished. appeared dosely related to stomatal apertuře at low g^ levels. However, intercellular CO2 concentration was not so much affected by stomatal closure. An important inter- and intra-genotypic variation in g^ was found at the initial sampling dates. Inter-genotypic variation for increased with time, probably as a result of a higher capacity for water uptake in some genotypes.
Responses of stem net photosynthetic rate (P^) to irradiance (/), temperature, vapor pressure, CO2 concentration, nitrogen content, and water potential were studied during early spring (March) and mid summer (latě July) in field populations of two stem photosynthesizing species introduced into Coastal California sites. Stem in Spartium junceum was inhibited in the summer compared with the spring due to low water potential and low tissue nitrogen content. Quantum yield decreased from March to July, along with a decrease in the demand fimction of the C, response curves. Stem conductance was lower at all vapor pressure deficits during the summer, but Cj at a Cg of 350 pmol moE* increased for S. junceum from spring to summer. The thermal optimum for stem did not change between the two seasons, but that of S. junceum was 5 °C higher than that for Cytisus scoparius. The demand function for the Cj curves of C. scoparius also decreased from spring to summer, but the Cj at a Cg of 350 pmol moT* remained unchanged between the seasons. Thus, the water use efficiency of S. junceum decreased in the summer compared with that of the spring while that of C. scoparius remained unchanged between seasons. There was little evidence for compensatory acclimation of stem F^ to changes in climatic conditions in these species.
The seasonal activities of the European pigeon tick, Argas reflexus, in Berlin were investigated (a) by trapping locomotory active ticks and (b) by determining the occurrence of tick-invasions into human habitations. Tick trapping was carried out in two tick-infested attics in 1988. Pigeons were available for ticks in one of the attics only, while a previously existing bird colony was expelled from the other. Ticks were trapped by means of smooth V- shaped metal gutters cemented to the attic walls. Trapped nymphal and adult ticks were marked and released into cracks of the attic wall inside the rectangular traps in two-weck-intervals. During the one-year-study a total of 2081 ticks was trapped, 83% of which were larvae, 10% nymphs, 4% females and 3% males. Only 4.4% of the 366 ticks marked were recaptured. There is strong evidence that locomotor activities of A. reflexus were restricted to host-seeking and returning to a resting-site after a blood meal. Activities of all postembryonic stages peaked from March through early June, irrespective of whether or not hosts were available to the ticks. The immature stages displayed another peak of activity in late summer/autumn. A total of 51 cases of A. reflexus-infested buildings was reported from the public to public-health offices in Berlin from April 1989 to March 1993, 45 of which represented tick invasions into human habitations. About 60% of them occurred in spring, thus largely confirming the results of seasonal trapping.
The seasonal changes of the nematode Camallanus anabantis Pearse, 1933, in the climbing perch (Anabas testudineus) from the freshwater swamps near Kalyani town, West Bengal, India were studied during the period from February 1988 to August 1989. The nematode exhibited a one-year cycle. Larvated females occurred in the fishes from October to February at a water temperature of 12“-29 °C. New infection of fishes occurred from February to May and occasionally in September. The fourth-stage larvae, the males, and the young females (without eggs), although irregularly, were found present throughout the year. Egg-laden females occurred in the fishes in August, October to February, and March.
The proteocephalid tapeworm Proteocephalus torulosus (Batsch, 1786) exhibited a marked seasonality in its occurrence and maturation in barbel (Barbus harhus L.) from the Jihlava River, South Moravia, Czech Republic. Recruitment took place in winter and early spring, growth and maturation in spring and gravid worms left the fish hosts in May; during summer and autumn, the parasite was almost absent from the fish population. Parasite burden was related to fish size, with larger barbel being more heavily infected than smaller ones.
Of 14,431 Clypeomorus bifasciata Sowerby, 1855 collected from Kuwait Bay between November 1992 and October 1993, 718 (5.0%) were shedding a total of 12 morphologically distinguishable ‘types’ of cercariae: 1 cystocercous, 2 echinos-tome, 1 furcocystocercous, 3 magnacercous, 2 megalurous, 1 microcercous and 2 ubiquità. Ubiquità I and furcocystocercous were the most prevalent species accounting for 66% and 25%, respectively, of total cercaria fauna. Double infections were recorded in only 6 (0.8%) of the infected snails. The overall prevalence of C. bifasciata shedding cercariae was highest (6-10%) in spring and summer, and species diversity was highest (11 species) in fall and spring. Seasonal variations in prevalence and diversity of cercariae were related to environmental factors and hosts behavior.
Leaf chlorophyll (Chl) content, net photosynthetic rate (P^) and biomass production were estimated at monthly intervals in Chukrasia tabularis, Dolichandrone atrovirem, Eugenia Jambolana, Gmelina arborea, Lannea coromandelica, Terminalia arjuna and Terminalia bellerica from September 1990 to August 1991. The leaves of all the seven tree species showed significantly higher Chl content during summer than in winter, when it was expressed on area and/or fresh mass basis. Chl concentration showed marked variations from month to month and these differed from one plant species to the other. Clear positive correlations were found between Chl content and and/or biomass production in all the seven deciduous forest tree species studied. The scope for screening and selecting the right type of tree species prospective for energy plantations can be based on a simple technique such as estimation of leaf Chl content and PN.
The ribulose 1,5-bisphosphate carboxylase (RuBPC) activity, protein content and net photosynthetic rate (P^) were estimated at monthly intervals from September 1990 to August 1991 in Chukrasia íabularis, Dolichandrom atrovirens, Eugenia jambolana, Gmelina arborea, Lamea coromandelica, Terminalia arjuna and Terminalia bellehca. The leaves of all these tree species showed significantly higher RuBPC activity during summer than in winter, when it was expressed on the basis of chlorophyll (Chl) content. RuBPC exhibited seasonal variations in its activity and these differed from one tree species to the other. When expressed on the basis of leaf area, the activity of RuBPC correlated with protein content, but not with P^.