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From April 1997 to June 1998 Nemurella pictetii populations were regularly sampled in two springstreams at 220 and 850 m a.s.l., respectively, in Hesse (Germany), at approximately 51°N. Random samples of larvae were taken at three week intervals during the vegetation period, and once a month during winter. Sex, instar, body length, head capsule width and wing pad length of all larvae were recorded. Temperatures were recorded every hour, temporal patterns of temperature agreed closely between sites. Mean winter lows were 3.9 °C at both sites, the mean summer high was 11.9 °C at the lower site, as opposed to 9.6 °C at the mountain site.At both sites, adult emergence started in May. At the mountain site, recruitment started in late July and continued into autumn. There was cohort splitting in the young generation. Some individuals grew rapidly until October–November, but last instar larvae first appeared in March the next year. 1600 degree-days above 0 °C were accumulated during complete development. At the lower site, recruitment began in early July, and cohort splitting also occurred. Fast growing summer recruits emerged as adults in late August, having accumulated only 700 degree-days (above 0 °C). Their offspring hatched in November-December and emerged the next spring, having accumulated also only 700 degree-days. However, only part of the population was bivoltine. Many of the summer recruits grew more slowly and accumulated close to 1900 degree days until they emerged the next spring, together with the offspring of their own fast-growing siblings. Dependence of growth rate on temperature could not be estimated and appears to vary with daylength. For example, 3–6 °C support growth and development provided daylength exceeds 10 hrs of light, or is rising.At both sites and in all cohorts individuals emerging earliest were larger than later emerging ones. The size decline is significantly correlated with number of days after the winter solstice. For the first time it is shown that the decline does not occur shortly before adult emergence but actually takes place several instars before the last. Size differences are then carried on, and amplified, during subsequent molts, until adulthood. The literature presently relates seasonal size declines of insects to high or rising temperatures experienced by larvae approaching adulthood. Our data show that, at least in Nemurella, this explanation fails. On average, females were distinctly larger than males. Differences in mean last instar size were noticed also between sites and years. They remain presently unexplained. The mean sex ratio in both populations was close to 1:1. 相似文献
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宁夏区域太阳日辐射通量计算方法的研究 总被引：1，自引：0，他引：1
利用银川站过去5 a的太阳日辐射观测资料(1981~1985)与大气外太阳辐射、日照时数、日照长度间的相关关系,确定了区域系数as。通过对bs的取值进行敏感测试,可得到一组最佳推算太阳辐射通量的区域系数:as=0.3,bs=0.5。用此系数和太阳日辐射通量计算公式,推算了银川站1986、1987年太阳日辐射通量并用观测值进行验证,结果表明:两者之间有很好的线性相关,R2=0.94,验证了区域系数的可信度。通过对银川站2 a(1986,1987)资料的平均误差、平均偏差、平均绝对偏差和均方根偏差的计算表明,结果与国内相关报道基本一致。对宁夏永宁站1989~2000年的太阳日辐射通量用区域系数进行估算,并与银川站的实际观测资料比较,结果显示永宁站太阳日辐射通量估算值和银川站实测值间有很好的线性关系,12 a间的方差最小值R2=0.88。 相似文献
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Yitzchak Gutterman 《Journal of Arid Environments》1997,36(4):611-622
Spergularia diandrais a common annual plant in the deserts of Israel. It displays a quantitative long-day response to flowering. The longer the daylength, from 8 to 18 h, the earlier the time of flowering. Tiny wind-dispersed seeds, which mature on plants under these daylengths, differed in their seed coat structure and size. In addition, in natural populations nine types of seeds were found: three plant genotypes with smooth, hairy or partially hairy seeds; and within each genotype there are three seed phenotypes: black, brown and yellow. The flowering and ‘escape’ strategy of seed dispersal diversity are discussed. 相似文献
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Physiology of Laminaria 总被引：1，自引：0，他引：1
Abstract. Sporophytes of Laminaria digitata and L. saccharina were collected from the shore at different times of year. Intact sporophytes of both species, and discs cut from L. digitata lamina tissue were maintained for several weeks in laboratory cultures under various nitrate, phosphate, temperature and daylength regimes. Substrate-saturated uptake rates of approximately 24 μgN g dry weight-1 h-1 from 20 μM nitrate and 8 μgP g dry weight-1 h-1 from 10 μM phosphate were more than sufficient to account for internal nitrogen and phosphorus accumulation. Other nitrogen sources - nitrite, ammonium and urea - were also taken up, independently of each other, and supported growth. During the late spring decline of ambient nutrient levels, when growth rates on the shore also decline markedly, enrichment with nitrate (15 μM) and phosphate (3μ) together prevented this decline and also maintained peak photosynthetic rates (net photosynthesis = 10.4 μlO2 cm-2 h-1) which otherwise dropped to 4.5 μO2 cm-2 h-1 over 47 days at ambient nutrient levels (0.5 μM nitrate and phosphate). Slow summer growth rates in June/July were enhanced to greater than spring peak values by combined nitrate (7.5 μM) and phosphate (1.8 μM) enrichment; neither was sufficient alone, although the individual nutrients were accumulated internally. A lesser, but significant enhancement was also achieved in September. In midwinter, nutrient enhancement itself (10.5 μM nitrate and 3.0 μM phosphate) had a small effect on growth rates only if summer water temperature (15°C) was used, but the dramatic effect of an increased photoperiod (7.5 to 17.5 h) was in excess of that expected for the increased radiant energy available. This was found to be due, at least in L. digitaia discs, to the re-establishment of a surface meristoderm in the dormant winter tissue; this was particularly active with high phosphate supply. Growth of the new lamina in January on the shore was much reduced if the old lamina was removed, although the time of initiation of new growth remained unchanged. In the laboratory, the old lamina was found to be a source of nitrogen for new lamina but not of fixed carbon or phosphorus. New lamina photosynthesis, manifest as mannitol accumulation, was directly proportional to phosphate supply up to at least 7.5 μM phosphate. Mannitol accumulation was then suppressed by a nitrate supply above 12 um, presumably by diversion of fixed carbon to other biosynthetic pathways. 相似文献
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