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Summary In a geographically wide distribution the life cycles of different populations of the cabbage moth Mamestra brossicae are adapted to a remarkable diversity of climatic conditions. This is undoubtedly a proof of its success in adaptation. Some populations living in regions characterized by a drought period interrupting the growth season are capable of distinguishing between one critical day length signalling the onset of the drought period and another signalling the end of the growth season. This study, therefore, is primarily concerned with the geographical patterns in the variability of the adaptional responses of populations exposed to environmental conditions requiring different strategies and tactics in, synchronizing individual, life cycles. It is also a contribution to our understanding of evolutionary mechanisms maintaining median responses to photoperiodically inductive day lengths in geographically different populations. The populations investigated originated from regions differing in predictability of the incidence, onset and duration of a drought period: Freiburg (48.0°N, Southern Germany), Avignon (44.0°N, Southern France), and Argelès (42.5°N, Southern France). Geographical variation with respect to both onset and duration of a drought period consequently results in clinal variation of the variability of innate day length thresholds triggering aestival dormancy and of innate duration of aestivation. In this paper we considered the influence of geographically changing temperatures on aestival dormancy induction. Even in southern populations of M. brassicae a temperature dependent switch off-mechanism exists which prevents aestival dormancy under certain environmental conditions. The effective temperatures vary geographically, too. What the geographical patterns in adaptive responses really are, is discussed.This research was supported by the Deutsche Forschungsgemeinschaft (Sa 259/3-1) 相似文献
125.
Summary Tree-ring data of naturally grown connifers were analyzed to evaluate the possibility of enhanced tree growth due to increased atmospheric CO2. Tree cores were obtained from 34 sites in four different climatic regions in the northern hemisphere. In each of the four regions, the sampling sites were located along ecological gradients between the subalpine treeline and low elevations and, sometimes, the arid forest border. Growth trends after 1950, when the atmospheric CO2 concentration increased by more than 30 l·l-1 indicate an increase in ring-widths at eight of the 34 sites. These chronologies were from sites which moderate temperature or water stress. In four cases the growth increase in the post-1950 period coincided with favorable climatic conditions. In the remaining four cases, the growth increase exceeded the upper bound response expected from CO2 enrichment experiments with seedling conifer species. Therefore, increased growth in any of the tree-ring chronologies examined could not be solely attributed to higher atmospheric CO2 concentrations.Major financial supporters: Swiss National Science Foundation (application no. 1.869-0.83); Swiss Federal Institute of Forestry Research, 8903 Birmensdorf, Switzerland; other financial supporters: Carbon Dioxide Research Division, U.S. Department of Energy under subcontract no. 11X-57507V with Martin Marietta Energy Systems, IncOperated by Martin Marietta Energy Systems, Inc., under contract DE-AC05-840R21400 with U.S. Department of Energy 相似文献
126.
Maize (Zea mays L.) and ricebean (Vigna umbellata [Thumb.] Ohwi and Ohashi) were grown in intercrop and monoculture on Tropaqualf soils under rainfed conditions in Northern
Thailand yearly from 1983 to 1986. De Wit's replacement design was used to compare intercrops and monocultures with a constant
plant density equivalent to 80 000 maize or 160 000 ricebean plants ha−1. Combined nitrogen was applied at varying levels to 200 kg N ha−1. In the final two seasons the intercrop ratio of maize: ricebean was also varied. At the time of maize maturity intercrops
yielded upt 49 kg ha−1 more N in the above ground plant parts than the best monoculture. Dry matter, grain and nitrogen yield of maize and ricebean
in intercrop relative to their monoculture yields (RY, relative yield) were significantly greater than their respective share
of the plant population. Relative yield totals (RYT) for grain, dry matter and nitrogen were always greater than 1.
Nitrogen uptake per maize plant increased with progressive replacement of maize by ricebean plants. This increase was similar
to that obtained by applying combined N. Available soil nitrogen tended to decrease with increasing maize:ricebean ratio.
Increasing the maize:ricebean ratio increased the % of nitrogen derived from fixation in ricebean, the increase being equivalent
to that obtained by decreasing combined nitrogen application. Approximately the same amount of fertilizer and soil nitrogen
was taken up by maize plus ricebean in intercrop as the maize monoculture. The results suggest that the improved nitrogen
economy of the intercrop resulted from the strong competitiveness of maize in the use of mineral nitrogen and the enhancement
of nitrogen fixation in intercropped ricebean which made it less dependent on the depleted pool of soil nitrogen. 相似文献
127.
The15N abundance of plants usually closely reflects the15N abundance of their major immediate N source(s); plant-available soil N in the case of non-N2-fixing plants and atmospheric N2 in the case of N2 fixing plants. The15N abundance values of these sources are usually sufficiently different from each other that a significant and systematic difference in the15N abundance between the two kinds of plants can be detected. This difference provides the basis for the natural15N abundance method of estimating the relative contribution of atmospheric N2 to N2-fixing plants growing in natural and agricultural settings. The natural15N abundance method has certain advantages over more conventional methods, particularly in natural ecosystems, since disturbance of the system is not required and the measurements may be made on samples dried in the field. This method has been tested mainly with legumes in agricultural settings. The tests have demonstrated the validity of this method of arriving at semi-quantitative estimates of biological N2-fixation in these settings. More limited tests and applications have been made for legumes in natural ecosystems. An understanding of the limits and utility of this method in these systems is beginning to emerge. Examples of systematic measurements of differences in15N abundance between non-legume N2-fixing systems and neighbouring non-fixing systems are more unusual. In principle, application of the method to estimate N2-fixation by nodulated non-legumes, using the natural15N abundance method, is as feasible as estimating N2-fixation by legumes. Most of the studies involving N2-fixing non-legumes are with this type of system (e.g., Ceanothus, Chamabatia, Eleagnus, Alnus, Myrica, and so forth). Resuls of these studies are described. Applicability for associative N2-fixation is an empirical question, the answer to which probably depends upon the degree to which fixed N goes predominantly to the plant rather than to the soil N pool. The natural15N abundance method is probably not well suited to assessing the contribution of N2-fixation by free-living microorganisms in their natural habitat, particularly soil microorganisms.This work was supported in part by subcontracts under grants from the US National Science Foundation (DEB79-21971 and BSR821618) 相似文献
128.
Kucey R. M. N. Snitwongse P. Chaiwanakupt P. Wadisirisuk P. Siripaibool C. Arayangkool T. Boonkerd N. Rennie R. J. 《Plant and Soil》1988,108(1):33-41
Controlled environment and field studies were conducted to determine relationships between various measurements of N2 fixation using soybeans and to use these measures to evaluate a number ofBradyrhizobium japonicum strains for effectiveness in N2 fixation in Thai soils.15N dilution measurements of N2 fixation showed levels of fixation ranging from 32 to 161 kg N ha−1 depending on bacterial strain, host cultivar and location. Midseason measures of N2 fixation were correlated with each other, but not related measures taken at maturity. Ranking ofB. japonicum strains based on performance under controlled conditions in N-free media were highly correlated with rankings based on soybean
seed yields and N2 fixation under field conditions. This study showed that inoculation of soybeans with effectiveB. japonicum strains can result in significant increases in yield and uptake of N through fixation. The most effective strains tested
for use in Thai conditions were those isolated from Thai soils; however, effective strains from other locations were also
of benefit. 相似文献
129.
Effects and interactions of varying CaSO4 and NaCl levels on growth and nitrogen fixation ofLeucaena leucocephala K8 were examined. Leucaena was grown in nutrient solution at four levels of CaSO4 (0.5, 1.0, 2.5 and 5.0 mM) and NaCl (1, 25, 50 and 100 mM) in randomized blocks with five replications. While NaCl significantly reduced plant growth, additions of CaSO4 increased plant height, leaf number, and biomass of salt treated plants. For the nonsaline treatments, high CaSO4 levels slightly depressed growth, which contradicts suggestions that Leucaena has a high calcium requirement. A significant
calcium/sodium interaction was not seen for nodule number or weight. Nodule number was significantly depressed by 100 mM NaCl and nodule weight of the salt stressed plants significantly increased as CaSO4 concentration increased from 0.5 to 2.5 mM. Effects of NaCl and CaSO4 on nitrogen content of plant parts were inconclusive. The promotion of Leucaena salinity tolerance by addition of CaSO4 may be attributed to the effect of calcium in maintaing the selective permeability of membranes. 相似文献
130.
As part of our investigation of the mode of action of plant hormones in barley (Hordeum vulgare L.) aleurone layers, we have studied the expression of five identified and three unidentified mRNA species in the presence of exogenous gibberellic acid (GA3) and abscisic acid. Three of the mRNAs are GA3-inducible, three are suppressed by GA3, and two are constitutive. The extent of the GA3 effect differs considerably for both inducible and suppressible mRNAs. For example, a ten-fold higher concentration of GA3 (10-8 M) is required for full induction of the high-pl group -amylase mRNA than is required for the low-pI -amylase mRNA (10-9 M). Temporal regulation of mRNA abundance also varies between the two -amylase isoenzyme groups. The three GA3-suppressible mRNA species studied, alcohol dehydrogenase (ADH1), a probable amylase and protease inhibitor, and an unidentified barley mRNA species also varied in response to GA3. The ADH1 mRNA decreased drastically within 8 h of GA3 treatment, whereas the other two began to decrease in abundance only after 12–16 h of GA3 treatment. Abscisic-acid treatment counteracted the GA3 effects for both the inducible and suppressible mRNA species. Comparison of -amylase-mRNA levels and -amylase-synthesis rates showed a strong correlation between the two parameters, the only exception being a lack of -amylase synthesis in the presence of -amylase mRNA at low GA3 concentrations. Therefore, the expression of -amylase seems to be regulated primarily by its mRNA levels.Abbreviations ABA
abscisic acid
- ADH1
alcohol dehydrogenase 1
- cDNA
copy DNA
- GA3
gibberellic acid
- PAPI
probable amylase/protease inhibitor 相似文献