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151.
Modelled effects of precipitation on ecosystem carbon and water dynamics in different climatic zones
DIETER GERTEN YIQI LUO GUERRIC Le MAIRE WILLIAM J. PARTON CINDY KEOUGH ENSHENG WENG CLAUS BEIER PHILIPPE CIAIS WOLFGANG CRAMER JEFFREY S. DUKES PAUL J. HANSON ALAN A. K. KNAPP SUNE LINDER DAN NEPSTAD LINDSEY RUSTAD ALWYN SOWERBY 《Global Change Biology》2008,14(10):2365-2379
The ongoing changes in the global climate expose the world's ecosystems not only to increasing CO2 concentrations and temperatures but also to altered precipitation (P) regimes. Using four well-established process-based ecosystem models (LPJ, DayCent, ORCHIDEE, TECO), we explored effects of potential P changes on water limitation and net primary production (NPP) in seven terrestrial ecosystems with distinctive vegetation types in different hydroclimatic zones. We found that NPP responses to P changes differed not only among sites but also within a year at a given site. The magnitudes of NPP change were basically determined by the degree of ecosystem water limitation, which was quantified here using the ratio between atmospheric transpirational demand and soil water supply. Humid sites and/or periods were least responsive to any change in P as compared with moderately humid or dry sites/periods. We also found that NPP responded more strongly to doubling or halving of P amount and a seasonal shift in P occurrence than that to altered P frequency and intensity at constant annual amounts. The findings were highly robust across the four models especially in terms of the direction of changes and largely consistent with earlier P manipulation experiments and modelling results. Overall, this study underscores the widespread importance of P as a driver of change in ecosystems, although the ultimate response of a particular site will depend on the detailed nature and seasonal timing of P change. 相似文献
152.
WOLFGANG SCHUMANN 《Physiological Entomology》1974,49(1):89-96
The variation in copulatory activity in three strains of Culex pipiens is investigated and the results are discussed in relation to genetic control of mosquito populations. 相似文献
153.
SYNOPSIS. AS theory rules method, the methodological proceduresapplied to morphological explanation have to be derived fromthe law-like properties of the objects under investigation.The explanation of organismic constructions has to be basedon the hydraulic principle which describes organisms as systemscomposed of fluid contained within flexiblemembranes. This insightestablishes a supra-molecular causal principle which, in itsgenerality for morphological explanation, parallels the biochemicalprinciples of molecular biology on the molecular level. Everyform and architectural arrangement has to be conceived as theresult of the form-enforcing influence of mechanical elementsthat operatewithin an integrated mechanically coherent system.An adequate explanation of morphological configuration has toelaborate the organization of the constructional whole and explainits properties as the result of a gradual transformation processthat is constrained by internal mechanical principles. The theoriesdeveloped by such a procedure are open to criticism and canbe tested and corroborated by reference to experiments conductedby nature. 相似文献
154.
155.
ABSTRACT. The locomotor activity patterns of wildtype Drosophila melanogaster and the mutants so (sine oculis) and sol (small optic lobes) were investigated. In all strains the proportions showing circadian rhythmicity, arrhythmicity and more complex patterns which could not be thus classified were similar. The occurrence of abnormal activity patterns is thus not a property of the mutation as previously claimed (Mack & Engelmann, 1981). In flies with a distinct circadian rhythmicity, the period lengths (τ) varied between strains, τ for wildtype Italy and the mutant so was longer than for wildtype Berlin and the mutant sol. As different τ's have been reported by others, τ does not seem to be closely determined for Drosophila melanogaster. Many flies exhibited two rhythms simultaneously, one with τ shorter and one with τ longer than 24 h, apparently implying two-oscillator control of the locomotor activity. The eyeless so mutants were entrained by LD cycles, so the compound eyes are not necessary, and so must possess the relevant photoreceptor(s) elsewhere. This may therefore also be true for the wildtype. Histology of the so adults revealed no correlation between the degree of reduction in the medulla and the occurrence of abnormal activity patterns. Since the only structures common to the medulla of so and sol are known to be large tangential cells, it is concluded that either they are of importance for the rhythmic system, or the oscillator(s) controlling locomotor activity is (are) not located in the medulla. 相似文献