The effect of past changes in inter‐annual temperature variability on tree distribution limits

Aim The northern limits of temperate broadleaved species in Fennoscanndia are controlled by their requirements for summer warmth for successful regeneration and growth as well as by the detrimental effects of winter cold on plant tissue. However, occurrences of meteorological conditions with detrimental effects on individual species are rare events rather than a reflection of average conditions. We explore the effect of changes in inter‐annual temperature variability on the abundances of the tree species Tilia cordata, Quercus robur and Ulmus glabra near their distribution limits using a process‐based model of ecosystem dynamics. Location A site in central Sweden and a site in southern Finland were used as examples for the ecotone between boreal and temperate forests in Fennoscandia. The Finnish site was selected because of the availability of varve‐thickness data. Methods The dynamic vegetation model LPJ‐GUESS was run with four scenarios of inter‐annual temperature forcing for the last 10,000 years. In one scenario the variability in the thickness of summer and winter varves from the annually laminated lake in Finland was used as a proxy for past inter‐annual temperature variability. Two scenarios were devised to explore systematically the effect of stepwise changes in the variance and shape parameter of a probability distribution. All variability scenarios were run both with and without the long‐term trend in Holocene temperature change predicted by an atmospheric general circulation model. Results Directional changes in inter‐annual temperature variability have significant effects on simulated tree distribution limits through time. Variations in inter‐annual temperature variability alone are shown to alter vegetation composition by magnitudes similar to the magnitude of changes driven by variation in mean temperatures. Main conclusions The varve data indicate that inter‐annual climate variability has changed in the past. The model results show that past changes in species abundance can be explained by changes in the inter‐annual variability of climate parameters as well as by mean climate. Because inter‐annual climatic variability is predicted to change in the future, this component of climate change should be taken into account both when making projections of future plant distributions and when interpreting vegetation history.     

Annual cycles of four flea species in the central Negev desert

Bionomics of fleas (Siphonaptera) parasitizing rodent hosts, mostly the gerbil Gerbillus dasyurus (Wagner) and the jird Meriones crassus Sundevall (Gerbillidae), were investigated in the central Negev desert of Israel. Populations were sampled weekly (by Sherman trapping of hosts) from August 2000 to July 2001. Among 1055 fleas of nine species captured, four species predominated (94%). Two species of Pulicidae, Xenopsylla dipodilli Smit and X. ramesis (Rothschild), reproduced perennially, whereas adults of Nosopsyllus iranus theodori Smit (Ceratophyllidae) and Stenoponia tripectinata medialis Jordan (Hystrichopsyllidae) occurred only in cool months (October-March). During their main activity season on the most infested host species (estimated from > 300 trap-nights/month), prevalence of these four flea species reached 40-70%, 20-30%, 100% and 50-70%, respectively, with infestation intensities of 2-2.7, 7-12, 2-3.5 and 2.5-7 fleas per infested rodent, respectively. Xenopsylla dipodilli oviposition peaked during autumn with parous rate > 80% by September-October. During December-April, the majority of X. dipodilli females were immature and/or nulliparous (defined as having mature ovaries but no follicular relics). In contrast, X. ramesis had two reproductive peaks, in mid-spring and autumn, evidenced by the influx of immature females in late spring and summer (30-40%) and in winter (20-30%) after maximal parous rates: 80-100% in March-April and 95-100% in October-November. Nosopsyllus iranus theodori and Stenoponia tripectinata medialis adults occurred only during cool months. At the beginning of activity, during October-November, the sex ratio of N. i. theodori was strongly biased to females (86%) that were immature and/or nulliparous. In winter, adult females were 52-65% parous and 10-32% immature. In March, as the adult population of N. i. theodori declined, 78% of females were parous and 12% immature. Seasonal activity of S. t. medialis (November-March) was shorter than for the other three species; females were predominantly nulliparous in November (80%), after which the proportion of parous females increased gradually to 84% in February. Two females of S. t. medialis collected in March were mature but nulliparous, suggesting that this species of flea might 'oversummer' (as pupae or teneral adults) in the cocooned stage.     

Oak canopy effects on the distribution patterns of two annual grasses: the role of competition and soil nutrients

Within the oak woodlands of California there is often a distinct shift in the botanical composition between the open grassland and the herbaceous understory beneath oak canopy. Botanical sampling at two woodland sites indicated that the annual grass Bromus diandrus was dominant under deciduous blue oak canopy, while a congener, Bromus hordeaceus, was dominant in open grassland. We examined the relative importance of congeneric competition and edaphic factors in creating these differences in species distribution in two separate field experiments that manipulated both congeneric and intraspecific competition, as well as soil type. We used the demographic measure of relative reproductive rate as an index of population growth. In general, demographic performance correctly predicted the distribution of the two annual grasses in the field. Our results indicate that reduced abundance of B. hordeaceus under canopy reflects the negative effects of competition with B. diandrus. In contrast, B. diandrus is little affected by competition from B. hordeaceus. The reduced abundance of B. diandrus in open grassland may result, in part, from its inability to adapt as well as B. hordeaceus to lower nutrient availability in soils of the open grassland.     

Diagnosis of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) in the UK

Light leaf spot lesions were generally first observed as light green areas on leaves of UK winter oilseed rape crops in January or February and later became brittle and bleached. Elongated lesions, which were brown with indistinct edges, developed on stems in the spring and summer, when lesions were also observed on flower buds, pedicels and pods. Development of diagnostic white pustules (spore masses of Pyrenopeziza brassicae, which erupt through surfaces of infected tissues) for confirmation of light leaf spot infection on symptomless plants or plants with indistinct or ambiguous symptoms in the autumn, winter or spring was enhanced by incubating plants in polyethylene bags. In experiments with artificially inoculated plants, glasshouse-grown plants exposed in infected crops and plants sampled from crops, white pustules developed at all incubation temperatures from 2^oC to 20^oC on infected leaves of different cultivars. The period of incubation required before the appearance of pustules decreased as the time that had already elapsed since the initial infection increased. The longest periods of incubation were required at the lowest temperatures (2^oC or 5^oC) but leaves senesced and abscised from plants most quickly at the highest temperatures (15^oC or 20^oC), suggesting that the optimal incubation temperature was between 10^oC and 15^oC.     

Growth,Net Production,Litter Decomposition,and Net Nitrogen Accumulation by Epiphytic Bryophytes in a Tropical Montane Forest1

To understand the ecological roles of epiphytic bryophytes in the carbon (C) and nitrogen (N) cycles of a tropical montane forest, we used samples in enclosures to estimate rates of growth, net production, and N accumulation by shoots in the canopy, and litterbags, to estimate rates of decomposition and N dynamics of epiphytic bryophyte litter in the canopy and on the forest floor in Monteverde, Costa Rica. Growth of epiphytic bryophytes was estimated at 30.0–49.9 percent/yr, net production at 122–203 g/m²/yr, and N accumulation at 1.8–3.0 g N/m²/yr. Cumulative mass loss from litterbags after one and two years in the canopy was 17 ± 2 and 19 ± 2 percent (mean ± 1 SE) of initial sample mass, respectively, and mass loss from litter and green shoots in litterbags after one year on the forest floor was 29 ± 2 and 45 ± 3 percent, respectively. Approximately 30 percent of the initial N mass was released rapidly from litter in both locations. Nitrogen loss from green shoots on the forest floor was greater; about 47 percent of the initial N mass was lost within the first three months. There was no evidence for net N immobilization by litter or green shoots, but the remaining N in litter was apparently recalcitrant. Annual net accumulation of C and N by epiphytic bryophytes was estimated at 37–64 g C/m²/yr and 0.8–1.3 g N/m²/yr, respectively. Previous research at this site indicated that epiphytic bryophytes retain inorganic N from atmospheric deposition to the canopy. Therefore, they play a major role in transforming N from mobile to highly recalcitrant forms in this ecosystem.     

Immunochemical detection of precursor proteins of yolk and vitelline envelope, and their annual changes in the blood of Diodon holocanthus

Two distinct groups of female-specific proteins, vitellogenin (VTG) and vitelline envelope proteins (VEP), were detected in the blood of the porcupine fish Diodon holocanthus , and annual changes in concentration were measured immunochemically. Using antisera against yolk proteins (ab.a-E) and VEP (ab. a-VEP), VTG and VEP could be detected in the blood of maturing female fish and oestradiol-17β (E₂)-treated fish. Neither protein was detected in the blood of male fish. Immunohistochemistry showed that yolk globules and the vitelline envelope enclosing developing oocytes stained with ab.a-E. The vitelline envelope was stained specifically with ab.a-VEP. Hepatocytes from the E2-treated fish had immunoreactivity with both antisera. Thus, VTG and VEP appear to be synthesized in the liver by direct stimulation of E₂, released into the circulation, and incorporated into respective target sites. VTG and VEP in female serum maintained high levels from April until June, suggesting that yolk accumulation, as well as vitelline envelope formation, are occurring actively during these months. Unlike VTG, small amounts of VEP were detected between December and March, suggesting that vitelline envelope formation precedes yolk accumulation and that a slightly different hormonal regulation exists in the synthesis of both proteins in the liver during the early phase of oogenesis.     

The role of calcium ions in freezing injuries of winter oilseed rape leaves. Effects of calcium channel blockers and mimesis by calcium ionophore

Calcium ionophore A23187 allowing for a calcium ion influx from an apoplast to a cytoplasm, mimicked symptoms of the frost-induced injuries in winter oilseed rape leaves, as estimated by the conductivity method. Both calcium ionophore and freezing treatment induced degradation of phosphatidylcholine. On the other hand lanthanum and gadolinum ions as well as verapamil, the inhibitors of calcium ion channels, decreased the degree of the frost-induced injuries. Lanthanum ions prevented the frost-induced degradation of PC. It is proposed that freezing alters the functioning of calcium ion channels which results in calcium ion influx into a cytosol. This in turn may lead to a degradation of cell membranes.     

长爪沙鼠贮食习性的研究

在内蒙古地区,由于野外食物条件的季节变化极为明显,许多种鼠类,特别是不冬眠鼠类,都形成了贮食习惯。对于长爪沙鼠（Ｍｅｒｉｏｎｅｓｕｎｇｕｉｃｕｌａｔｕｓ,简称沙鼠）,夏武平等介绍了内蒙古宝昌县的田间沙鼠洞穴贮粮情况［１］,赵肯堂描述过土默特旗田间沙鼠...