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81.
Ulrich Lüttge 《Die Naturwissenschaften》1997,84(12):526-534
Tintenstrich communities receive their name from the black strips on rocks, which are particularly spectacular on the background of white
limestone and dolomite. They are dominated by cyanobacteria, green photosynthesizing procaryotes. However, cyanobacterial
crusts are ubiquitous and much more widespread. On bare substratum on walls and rocks in temperate, arid, and tropical zones
they are subject to severe stress by insolation, heat, and either too little or too much water. An array of ecophysiological
traits allow them to endure this multifactorial stress. Particular features of their photosynthetic membranes may facilitate
dissipation of surplus photosynthetically active radiation; special sun-screen pigments protect them from UV radiation, they
are desiccation tolerant, concentrate inorganic carbon for photosynthetic fixation, and assimilate atmospheric dinitrogen.
With their own success on bare substratum they become pioneers for other organisms. 相似文献
82.
Ommatidia (the compound eye's functional units) in insects are formed by the recruitment of undifferentiated cells under
the control of signalling factors. During this process, a sequence of "preclusters" composed of specifically arranged precursor
cells is followed. In the growth zone of the eye of Triops, an ancestral crustacean, we observed a patterning process that corresponds well with that of insects. In both taxa, clusters
with arc-like, five-cell and eight-cell patterns are found, and the sequence in which the photoreceptor or R-cells of each
ommatidium become identifiable is basically the same. The first to appear are R8-like and R2/5-like cells, second are R3/4-like,
and third are R1/6- and R7-like cells (if the fly's cell-numbering system is used). Thus, the morphogenetic steps during which
the cell identities and the cellular architecture of the ommatidia develop appear to be conserved between these arthropod
groups. Furthermore, the individual cells and cell pairs which build an insect ommatidium seem to have their homologues in
crustaceans. In the evolution of developmental processes, intercellular recruitment seems to be a mechanism operating on the
level of single cells even in distantly related species.
Received: 12 May 2000 / Accepted in revised form: 17 May 2000 相似文献
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89.
Yuquan W. Zhang Bruce A. McCarl Yibo Luan Ulrich Kleinwechter 《Mitigation and Adaptation Strategies for Global Change》2018,23(5):685-701
China has announced plans to stabilize its pesticide use by 2020. Yet, future climate change will possibly increase the difficulty of meeting this goal. This study uses econometric estimation to explore how climate impacts Chinese pesticide usage and subsequently to project the future implications of climate change on pesticide use. The results indicate that both atmospheric temperature and precipitation increase pesticide usage. Under current climate change projections, pesticide usage will rise by +1.1 to 2.5% by 2040, +2.4 to 9.1% by 2070, and +2.6 to 18.3% by 2100. Linearly extrapolating the results to 2020 yields an approximately 0.5 to 1.2% increase. Thus, to achieve stabilization, more severe actions are needed to address this increase. Possible actions to achieve the reductions needed include using better monitoring and early warning networks so as to permit early responses to climate change-stimulated increases, enhancing information dissemination, altering crop mix, and promoting nonchemical control means. Additionally, given that increased pesticide usage generally increases health and environmental damage, there may be a need to more widely disseminate safe application procedure information while also strengthening compliance with food safety regulations. Furthermore, pest control strategies will need to be capable of evolving as climate change proceeds. Globally, efforts could be made to (1) scale up agrometeorological services, especially in developing countries; (2) use international frameworks to better align the environmental and health standards in developing countries with those in developed countries; and (3) adapt integrated pest management practices to climate change, especially for fruits and vegetables. 相似文献
90.
Tobias Mette Axel Albrecht Christian Ammer Peter Biber Ulrich Kohnle Hans Pretzsch 《Ecological modelling》2009,220(13-14):1670-1680
Forest growth simulators go beyond a mere tabulation of empirical measurements by employing biometric models that functionally describe the dependence of forest growth of the initial forest structure, growth conditions and management regime. This makes them very flexible and allows predicting growth reactions for unknown and/or complex forest growth scenarios. When simulation outcomes are to be used in silvicultural strategic planning, the results are of direct and delicate importance, and the correct simulator performance must be ascertained. This is especially so when the considered forest situation differs from the forest data used to parameterise the model (e.g. different geographical region).In this article, the forest growth simulator SILVA (version 2.2) was validated for 55 long-term experimental plots of mature mixed Silver fir–Norway spruce stands in southwest Germany (Picea abies, Abies alba). The evaluation was restricted to the upper canopy trees during the survey period 1989–2004. Following the general evaluation criteria for ecological models from [Vanclay, J.K., Skovsgaard, J.P., 1997. Evaluating forest growth models. Ecol. Mod. 98, 1–12], a specific methodology was developed to evaluate the simulated height and diameter growth on the basis of forest growth principles.The qualitative analysis proved the SILVA growth algorithms to be in accordance with physiologically based standard growth equations. The quantitative evaluation was limited by incomplete knowledge of the site conditions. To overcome this problem, the experimental plots were regarded as a “heterogeneous growth series” which allows analysing the growth behaviour in a more general way. It could be shown that for the given data set, the SILVA simulations produced an overestimation of height growth (median: +61% spruce, +12% fir), and an underestimation of diameter growth and competition sensitivity (median: ?16% spruce, ?70% fir). The errors partially compensated in the volume growth resulting in an overall over-/underestimation of +9% for spruce and ?58% for fir (median).The unbalanced height and diameter growth cannot be compensated by a change in the site conditions because this affects both height and diameter growth either positive or negative. Hence, an adjustment of selected parameterisation values appears to offer the best solution to adapt SILVA to the considered forest situation. This approach of adaptive parameterisation is discussed against a more general background of deductive vs. inductive forest growth modelling. 相似文献