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141.
G. M. Littlejohn R. de V. Pienaar 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,88(8):949-955
Thinopyrum distichum is indigenous to the southern and south western coastal shores of South Africa. Like many of the Thinopyrum species it can be hybridized with wheat. The resulting progeny treated with colchicine produce fertile amphiploids. The need to distinguish the Th. Distichum chromosomes from one another and from those of wheat prompted the investigation of the C-band distribution. The chromosome pairs of Th. distichum were distiguishable from each other and from those of wheat using C-band patterns, morphology and size as identification criteria. The chromosomes ranged from heterobrachial to metacentric with interstitial and telomeric C-bands. The C-band patterns of Th. distichum were similar, but not identical, to those of other Thinopyrum species. 相似文献
142.
Increased biomass production in terrestrial ecosystems with elevated atmospheric CO2 may be constrained by nutrient limitations as a result of increased requirement or reduced availability caused by reduced
turnover rates of nutrients. To determine the short-term impact of nitrogen (N) fertilization on plant biomass production
under elevated CO2, we compared the response of N-fertilized tallgrass prairie at ambient and twice-ambient CO2 levels over a 2-year period. Native tallgrass prairie plots (4.5 m diameter) were exposed continuously (24 h) to ambient
and twice-ambient CO2 from 1 April to 26 October. We compared our results to an unfertilized companion experiment on the same research site. Above-
and belowground biomass production and leaf area of fertilized plots were greater with elevated than ambient CO2 in both years. The increase in biomass at high CO2 occurred mainly aboveground in 1991, a dry year, and belowground in 1990, a wet year. Nitrogen concentration was lower in
plants exposed to elevated CO2, but total standing crop N was greater at high CO2. Increased root biomass under elevated CO2 apparently increased N uptake. The biomass production response to elevated CO2 was much greater on N-fertilized than unfertilized prairie, particularly in the dry year. We conclude that biomass production
response to elevated CO2 was suppressed by N limitation in years with below-normal precipitation. Reduced N concentration in above- and belowground
biomass could slow microbial degradation of soil organic matter and surface litter, thereby exacerbating N limitation in the
long term. 相似文献
143.
Nutrient distribution in a Swedish tree species experiment 总被引:2,自引:0,他引:2
The influence of four tree species on the distribution of nutrients between different compartments of the ecosystem was examined.
In a randomized block (n=3) experiment in south-western Sweden, Ca, Mg and K were determined as exchangeable amounts in the
mineral soil and as total amounts in the O+A1 horizons (topsoil) and in the aboveground tree biomass. N contents were determined in all compartments as well as P contents
of the aboveground tree biomass and the topsoil. The four tree species planted were: silver fir [Abies alba Mill.] (AA), grand fir [Abies grandis Lindl.] (AG), Norway spruce [Picea abies L. Karst.] (PA) and Japanese larch [Larix leptolepis (Sieb. och Zucc.) Endl.] (LL). At the age of 35–36 years, the total stemwood production of the most productive species, AG,
was estimated at 471 m3 ha−1. In relation to AG, LL had produced 80%, PA 73% and AA 37%.
The system totals [aboveground tree biomass total + topsoil total + exchangeable (Ca, Mg, K) or total (N) in the mineral soil]
of Ca, K and N did not differ significantly at the 5% level between the investigated species. For Mg, the system total in
LL was significantly higher than for the other species.
There was an indication that LL and AA contained higher amounts of Ca, Mg, K and N in the topsoil but less in the biomass
than did AG and PA (partly significant). In the mineral soil, there were no significant differences in the exchangeable pools
of Ca and K, nor in the total amounts of N.
The biomass nutrient concentrations generally decreased in the order: AA > PA > AG > LL. At stem or whole-tree harvest, the
Ca export per biomass unit would more than double in the case of PA compared to LL. LL also contained less N in the biomass
than the other species. However, the N content in the biomass did not differ between the most (AG) and the least (AA) productive
species, although the production of dry weight biomass (standing + harvested) of AG had been twice that of AA. It is concluded
that the nutrient budget of a managed forest may vary considerably depending on the choice of tree species. 相似文献
144.
J. Del Val Pérez J. E. Fa J. Castroviejo F. J. Purroy 《Biodiversity and Conservation》1994,3(9):868-892
The status of 50 taxonomically unique bird taxa found in Bioko is described. A complete updated species list for birds in Bioko is also given. Notes on habitat occupied and altitudinal distribution of each species as well as information on their general abundance is also included. Species distributions may have been affected by habitat modifications brought about by humans but most taxonomically unique forms are found in the montane areas. Comparisons are made with the neighbouring Mount Cameroon area. 相似文献
145.
To what extent some microbial index ratios are suitable for use as early criteria for the level of compost stability during aerobic composting of coniferous sawdust and bark at mesophilic conditions was studied. Evolution of the specific respiration activity (CO2-C/biomass C) and the ratios between some groups of microorganisms were followed as a function of composting time. The specific respiration activity was found to be an early and most reliable indicator of compost stability. The peroxidase and polyphenoloxidase enzyme activity during composting, as well as the composition of newly-formed humus substances were studied. The duration of composting increased the quality of newly-formed humus substances (Ch.a.:Cf.a ratio; Ca-complexed humic acid and resistance of organo-mineral complexes). The quality of humus substances could be used to assess compost stability. However, the results can be applied only under defined conditions. 相似文献
146.
Synopsis Similarities between the freshwater fish faunas of 52 west African rivers have been investigated and three main zoogeographic regions recognized. The Sudanian region includes all rivers from Senegal to the Omo, as well as coastal basins from Ivory Coast to the Cross and the Wouri. The Upper Guinean region comprises the coastal basins from Guinea to Liberia and the Lower Guinean one, the coastal rivers of Cameroon and Gaboon. The Sudanian region can be sub-divided into a Sudanian region sensu stricto, including the Sahelo-Sudanese rivers, and the Eburneo-Ghanean region corresponding to coastal basins from the Cess (or Nipoué, Ivory Coast) to the Pra (Ghana). These delimitations give an highly significant within region faunal homogeneity, even if the effect of geographical proximity between rivers is removed. 21 to 71% of the fish species in each region are endemics. The present patterns of distribution are the result of past climatic and geological events affecting west Africa and, given this framework, the role of alternating wet and dry periods during the early Quarternary is emphasized as well as the importance of mountains as dispersal barriers. Role of recent river connections and links via lagoon is emphasized in explaining river faunal similarities within biogeographical regions. 相似文献
147.
通过空间分布型指数分析,甘薯象对薯块、著株危害空间分布型为随机分布或均匀分布;同时确定了理论抽样数 相似文献
148.
Chromosome numbers were determined for 340 plants ofCarex conica from 83 populations in Japan. Six aneuploids, 2n=32, 33, 34, 36, 37 and 38, were found. Plants with even diploid chromosome numbers 2n=32, 34, and 36 were the most common and had different geographical distributions. Individuals with 2n=32 were from islands in the Seto Inland Sea and nearby coastal areas of the Chugoku District of Honshu; those with 2n=34 were from the Kanto, Chubu and Kinki Districts of Honshu; those with 2n=36 were from the mountainous areas of Chugoku, Shikoku and Kyushu Districts. Canonical discriminant analysis of 17 morphological
characters demonstrated that the plants with 2n=32 were clearly distinct from those with 2n=34 or 36. All four aneuploids with even chromosome numbers showed normal bivalent pairing at meiotic metaphase I and probably
represent cytogenetically stable cytodemes. Plants with 2n=33 had one heteromorphic trivalent and 15 bivalents, indicating a structural mutation. At mitotic metaphase I, one chromosome
was markedly larger than the others, suggesting that the 2n=33 plants arose from 2n=34 plants by fusion of two chromsomes. The plant with 2n=37 was intermediate in morphology betweenCarex conica (2n=36) andC. morrowii (2n=38) and probably originated as an interspecific hybrid between these species. 相似文献
149.
Connections among species-abundance (i-m
i
), species-frequency (i-F
i
), and species-sample size (S
n
-n) relationships were examined on the basis of the mapping data of a natural forest in Thailand. The spatial distribution of
individual trees without any discrimination of species was nearly random. Provided that the spatial distribution of each species
was random, thei-m
i
and thei-F
i
relationship was reconstructed from each other in terms of the total number of species (S) and the total number of individuals (N) in the data. The number of species (S
n
) in a subsample consisting ofn individuals was then obtained from thei-F
i
relationship. Logarithm ofS
n
increased with logn and showed a convex curve through the origin. The values of diversity indices based onN andS(orn andS
n
) were affected by sample size. These trends were further examined on the basis of 944 data sets of biotic communities and
three mathematical models of anS-N relationship. The properties of species-area relation were discussed in the light of these results. 相似文献
150.
The effects of highly and moderately acid soils on total biomass, biomass partitioning, fine root characteristics and nutritional
status of beech seedlings (Fagus sylvatica L.) were studied in a growth chamber experiment. In Haplic Arenosols seedlings grew slowly but equally well without damage
symptoms in a highly acid and a moderately acid soil horizon. The moderately acid Ah+Bw-horizon of a Eutric Cambisol was favourable to seedling growth. The fine root development was reduced in the highly acid
A+Bw-horizon of a Dystric Cambisol and in the Ah+E-horizon of a Haplic Podzol, the latter of which also caused increased mortality. Seedling growth in the B2-horizon of the Haplic Podzol was vigorous, in spite of a higher level of extractable Al and lower base saturation as compared
with the Ah+E-horizon. These results are interpreted in relation to soil acidity, soil Al and nutritional status of the seedlings. We
conclude that neither Al-toxicity nor nutrient deficiency cause the damage symptoms observed in the Ah+E-horizon of a Haplic Podzol and the fine root reduction in the A+Bw-horizon of a Dystric Cambisol. The damage symptoms of the PZhA treatment seems to be more the result of H-toxicity or H-related factors other than nutrient shortage or Al-toxicity. Other
pH-related toxic factors are discussed. 相似文献