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11.
Antarctic terrestrial ecosystems are briefly described, with emphasis on Signy Island in the maritime antarctic region, and the McMurdo oasis, southern Victoria Land, and Vestfold Hills in the continental antarctic region.As the largest and best known coastal ice-free oasis, the Vestfold Hills contain excellent examples of terrestrial sublithic, epilithic, chasmoendolithic, epiphytic and terricolous algal communities, as well as epilithic, endolithic, and epiphytic lichen communities, and moss communities. Many of the numerous lakes support dense communities of aquatic algae. 相似文献
12.
The relationships between physical, chemical and microbial characteristics of an aquatic ecosystem and the survival of E. coli have been studied. Two conditions of the ecosystem (warm and cold) are considered. T90 (time necessary for 90% of a bacterial population to die) in the warm situation shows an inverse exponential relationship with water temperature. Besides the direct relationship temperature-T90, there is an indirect effect of temperature upon T90 through the natural microflora of the water. The relationships between temperature and the heterotrophic population, and between the heterotrophic population and the bacterial consumers (P.F.U.), are exponential and linear, respectively. 相似文献
13.
湘南山区农业生态系统能量分析 总被引:3,自引:0,他引:3
一、引言由于农业系统的复杂性和存在较多的随机因素,对农业系统实行全面定量研究是比较困难的,仅从定性的描述和一些经济指标来判定系统的优劣及系统的特征是不理想的。而从能量观点对农业生态系统加以分析则是一个全面且能定量的方法,并且具有较强的客观性,能够反映农业生态系统最基本、最本质的关系。 相似文献
14.
The complete mitochondrial DNA (mtDNA) of the donkey and mtDNA comparisons among four closely related mammalian species-pairs 总被引:7,自引:0,他引:7
The nucleotide sequence of the complete mitochondrial genome of the donkey, Equus asinus, was determined. The length of the molecule is 16,670 bp. The length, however, is not absolute due to pronounced heteroplasmy
caused by variable numbers of two types of repetitive motifs in the control region. The sequence of the repeats is (a) 5′-CACACCCA
and (b) 5′-TGCGCGCA, respectively. The order of (a) and (b) can be expressed as {n[2(a)+(b)]+m(a)}. In 32 different clones analyzed the number of n and m ranged from 0 to 9 and 1 to 7. The two rRNA genes, the 13 peptide-coding genes, and the 22 tRNA genes of the donkey and the
horse, Equus caballus, were compared in detail. Total nucleotide difference outside the control region was 6.9%. Nucleotide difference between peptide-coding
genes ranged from 6.4% to 9.4% with a mean of 8.0%. In the inferred protein sequences of the 13 peptide-coding genes the amino
acid difference was 0.2–8.8%, and the mean for the 13 concatenated amino acid sequences was 1.9%. In the 22 tRNA genes, the
mean difference was 3.5%, and that in the two rRNA genes was 4.1%. The mtDNA differences between the donkey and the horse
suggest that the evolutionary separation of the two species occurred ≈9 million years ago. Analyses of differences among the
mtDNAs of three other species-pairs, harbor seal/grey seal, fin whale/blue whale, and Homo/common chimpanzee, showed that the relative evolutionary rate of individual peptide-coding genes varies among different species-pairs
and modes of comparison. The findings show that the superimposition of sequence data of one lineage for resolving and dating
evolutionary divergences of other lineages should be performed with caution unless based on comprehensive data.
Received: 15 October 1995 / Accepted: 15 April 1996 相似文献
15.
Epilithic bacterial and algal biomass were compared among a run, riffle, and pool along an open-canopy section of a third-order, temperate stream. Epilithic biofilms were sampled after 3, 7, 14, 21, 28, and 35 days colonization on unglazed ceramic tiles that were attached to plastic trays (n = 3) placed across each of the three habitats (i.e., run, riffle, pool). The diverse habitats and sampling regime were selected to provide a range in algal biomass so that potential covariation between epilithic bacterial and algal biomass could be assessed. There were significant differences among habitats and among trays within each habitat for both chlorophyll a and AFDM. Chlorophyll a and AFDM increased in the run and pool throughout the colonization period. In the riffle, chlorophyll a and AFDM increased rapidly early in colonization, then decreased. Epilithic bacterial biomass increased rapidly with no significant differences among the three habitats throughout colonization. Further, bacterial biomass did not correlate with either chlorophyll a or AFDM in any of the three habitats or on any of the sampling days. These results suggest that epilithic algal and bacterial biomass may be regulated by independent controls in some stream environments. 相似文献
16.
Cropping on jhum fallows in north-eartern India is predominantly done for one year in a jhum cycle. If second year cropping
is done, expanse of the forest land required for slashing and burning could be reduced significantly. We tested this hypothesis
in a young (6 yr) and an old (20 yr) jhum fallow. We also evaluated if the productivity during second year cropping could
be alleviated by auxiliary measures such as tilling the soil or application of fertilizers (chemical or farm-yard manure or
both in combination). The results demonstrate that the ecosystem productivity (total dry matter production) and economic yield
(rice grain production) decline with shortening of jhum cycle. Second year cropping causes a further decline in ecosystem
productivity in old jhum field, but not in young jhum field. Economic yield from second year cropping in its traditional form
(without any fertilizer treatment) is not much lower than that in the first year, and can be improved further by manuring
the soil. Tilling of soil improves neither ecosystem productivity nor economic yield. Different fertilization treatments respond
differently; while inorganic manuring enhances ecosystem productivity, a combination of inorganic and organic manuring improves
economic yield 相似文献
17.
Base cation biogeochemistry and weathering under oak and pine: a controlled long-term experiment 总被引:2,自引:0,他引:2
Large earthen-walled lysimeters at the San Dimas Experimental Forest in southern California present a unique opportunity to assess vegetation effects on biogeochemical processes and cation release by weathering in controlled soil-vegetation systems where archived samples of soil parent material are available for comparison. The lysimeters were filled in 1937 with homogenized fine sandy loam derived on site from the weathering of diorite, and planted in 1946 with scrub oak (Quercus dumosa) and Coulter pine (Pinus coulteri). Changes in base cation contents were measured in above-ground biomass, and total and exchangeable soil pools to a depth of 1 meter. All cations in the non-exchangeable soil pool decreased relative to the initial fill material, indicating release by weathering. Sodium and K were depleted from both exchangeable and non-exchangeable pools of the soils. Plant uptake of Na was minimal, whereas K storage in vegetation exceeded the loss from the exchangeable soil pool. In both soil-vegetation systems, but especially for oak, there was an increase in exchangeable Ca and Mg. For all base cations, storage in above-ground biomass was greater for oak, whereas losses by weathering from the non-exchangeable soil pool were greater under pine. Strong evidence supports biocycling as a controlling mechanism resulting in greater Ca and Mg release by weathering under pine. In addition, decreases in non-exchangeable Ca and Mg were strongly correlated to decrease in Si under oak, whereas no correlation was observed under pine. We conclude that weathering reactions or stoichiometry differed between vegetation types.Corresponding author 相似文献
18.
Soil nitrogen dynamics along a gradient of long-term soil development in a Hawaiian wet montane rainforest 总被引:1,自引:0,他引:1
Kanehiro Kitayama 《Plant and Soil》1996,183(2):253-262
I analyzed the rates of net N mineralization and nitrification of soils from seven sites in a Hawaiian wet montane forest. The sites differ in age, ranging from 400 to 4,100,000 yr, but are comparable in other variables (all at 1200 miasl with 4000 mm or more mean annual rainfall), and the chronosequence simulated a development of soils from basaltic lava. Soils were incubated for 20 days at 17.5 °C, which is nearly equivalent to a mean field air temperature of the sites, and at an elevated temperature of 25.5 °C under three treatments: 1) field-wet without amendments, 2) air dried to a permanent wilting point, and 3) fertilized with phosphate (NaH2PO4) at the rate of 50 g P per g dry soil. Both mineralization and nitrification rates varied significantly among the sites at the field temperature (p<.00001). Fractions of the mineralized organic matter (indexed by the N produced per g organic C) increased sharply from the youngest to the 5000-yr site before declining abruptly to a near constant value from the 9000 to the 1,400,000-yr sites. Total organic C in the top soils (<15 cm deep) increased almost linearly with age across the sites. Consequently, net NH4- and NO3-N produced on an area basis (g m-2 20 d-1) increased sharply from 0.2 in the youngest site to 1.2 in the 5000-yr site, then both became depressed once but steadily increased again. The fraction of organic matter mineralized, and the net N turnover rates were outstandingly high in the oldest site where a large amount of organic matter was observed; the topsoil organic matter which was used in this analysis appeared to be highly labile, whereas the subsurface organic matter could be relatively recalcitrant. As suggested by earlier workers, the initial increase in N turnover seemed to correspond to the increasing quantity of N in the soils through atmospheric deposition and biological fixation. The later decline in fraction of organic matter mineralized seemed to relate to increasing soil C/N ratios, increasingly recalcitrant organic matter, and poorer soil drainage with age. The elevated temperature treatment produced significantly higher amounts of N mineralization, except for the youngest site where N was most limiting, and for two sites where soil waterlogging might be severe. P fertilization invariably resulted in slower N turnovers, suggesting that soil microbes responded to added P causing N immobilization. The youngest site did not significantly respond to added P. The magnitude of immobilization was higher in older than in younger soils, suggesting that P more strongly limits microbial populations in the older soils. 相似文献
19.
Abstract. To test if low soil fertility and competition limit the performance of Mediterranean shrubs, and if the effects of competition on plant performance were modified by soil fertility, we subjected shrubs of Erica multiflora to a factorial field experiment of fertilization and removal of neighbours around target plants. After 18 months of treatment, fertilization had stimulated the growth of pre-existent sprouts and biomass allocation to stems into new sprouts, but decreased the frequency of sprout flowering. Removal of neighbours increased the number and biomass of new sprouts, the probability of sprout flowering and the biomass of flowers. Fertilization slightly enhanced sprout recruitment and the probability of sprout flowering when neighbours were removed, but did not modify the other parameters of plant performance. According to our results, both low soil fertility and competition limited plant performance. Competition was slightly more intense in fertilized plants, but only in determining sprout and flowering bud stimulation. 相似文献