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1.
The temporal variation of stoichiometry between consumed oxygen and oxidized carbon was investigated for the aerobic mineralization of leachates from aquatic macrophytes. Seven species of aquatic plants, viz. Cabomba piauhyensis, Cyperus giganteus, Egeria najas, Eichhornia azurea, Salvinia auriculata, Scirpus cubensisand Utricularia breviscapa, were collected from Òleo lagoon located in the floodplain of Mogi-Guacu river (São Paulo State, Brazil). After being collected, the plants were washed, oven-dried and triturated. In order to obtain the leachate, the fragments were submitted to an aqueous extraction (cold). Mineralization chambers were incubated at 20 °C containing leachates dissolved in water samples from Òleo lagoon to a final concentration of ca. 200 mg l–1on carbon basis. The chambers were maintained under aerobic conditions; the concentrations of the organic carbon (particulate and dissolved) and the dissolved oxygen were measured during approximately 80 days. Elemental analysis of the detritus and the concentrations of the remaining material (DOC and POC) were used to determine the amounts of mineralized organic carbon. The data were analyzed with first-order kinetics models, from which the daily rates of consumption (carbon and oxygen) and the stoichiometry (O/C) were determined. In the early phase of mineralization the O/C rates increased before reaching a maximum, after which they tended to decrease. For the mineralization of leachates from C. giganteus, S. auriculata and U. breviscapa, the decrease was relatively slow. For all substrata the initial values were smaller than 1, and ranged from 0.42 (S. cubensis) to 0.81 (C. piauhyensis). The maximum values were within the range from 0.58 (U. breviscapa) to 23.1 (E. najas) and at their highest 26th (C. piauhyensis) and 106th (C. giganteus) days. These variations are believed to be associated with the chemical composition of the leachates, with their transformations and alterations of metabolic pathways involved in the mineralization. 相似文献
2.
Summary The presence of a Ca2+ channel in the plasmalemma of tonoplast-freeNitellopsis obtusa cells was demonstrated and its characteristics were studied using current- and voltage-clamp techniques. A long-lasting inward membrane current (I
m
), recorded using a step voltage clamp, consisted of a single component without time-dependent inactivation. Increasing either [Ca2+]
o
or [Cl–]
o
1) enhanced the maximum amplitude of inwardI
m
((I
m
)
p
) and 2) shifted the peak voltage ((V
m
)
p
) at(I
m
)
p
to more positive values under ramp-shaped voltage clamping and 3) depolarized the peak value of action potentials. This behavior is consistent with predictions based on the Nernst equation for Ca2+ but not for Cl–. DIDS (4,4-diisothiocyano-2,2-disulfonic acid stilbene) did not suppress(I
m
)
p
in tonoplast-free cells, in contrast with its effect on normal cells. La3+ and nifedipine blocked(I
m
)
p
irreversibly. On the other hand, Ca2+ channel agonist, BAY K 8644 irreversibly enhanced(I
m
)
p
. Both Sr2+ influx and K+ efflux increased upon excitation. The charge carried by Sr2+ influx was compensated for by K+ efflux. It is concluded that only the Ca2+ channel is activated during plasmalemma excitation in tonoplast-free cells. In terms of the magnitude of(I
m
)
p
, Sr2+ could replace Ca2+, but Mn2+, Mg2+ and Ba2+ could not. External pH affected(I
m
)
p
and the membrane conductance (g
m
) at(I
m
)
p
((g
m
)
p
). Increasing the external ionic strength caused increases in both(I
m
)
p
and(g
m
)
p
, and shifted(V
m
)
p
to positive values. At the same time, Sr2+ influx increased. Thus Ca2+ channel activation seems to be enhanced by increasing external ionic strength. The possible involvement of surface potential is discussed. 相似文献
3.
A. K. Watson 《Journal of nematology》1986,18(2):149-153
The knapweed nematode, Subanguina picridis, forms galls on the leaves, stems, and root collar of Russian knapweed, Acroptilon repens. After being revived from a dormant, cryptobiotic state, second-stage juveniles required at least 1 month in a free-living state before becoming infective. Galls were induced on relatively slow-growing host plants that retained their apical meristems at or near the soil surface for 2-5 weeks. Galls developed extensive areas of nutritive tissue. The nematode was introduced from the Soviet Union and released in Canada for the biological control of Russian knapweed. 相似文献
4.
步氏巨猿的上犬齿与下第一前臼齿的咬合关系有两种主要类型:一是相似于“猿类”的,另一相似于“人类”的。前者为雄性个体所具有,后者为雌性个体所具有。另有少数个体的则是中间类型。上犬齿与下第一前臼齿的咬合特征的分类学上的意义是可疑的。至少就绝大部分雄性步氏巨猿个体来说,很难认为其犬齿是参与臼齿的功能。步氏巨猿下第一前臼齿之所以呈双尖类型,与其犬齿并无直接的关系。 相似文献
5.
J. C. Gloaguen 《Plant Ecology》1987,70(1):29-32
Four species of heath, occurring in the heathlands of Brittany, are compared regarding their water relations: Calluna vulgaris, Erica ciliaris, E. cinerea and E. tetralix. E. cinerea is unable to establish itself in wet heathland because of its intolerance of prolonged waterlogging. It is the Erica species best adapted to dry habitat conditions in Brittany. E. ciliaris canot establish itself in dry heathland and is less tolerant of waterlogging than E. tetralix. E. tetralix is the species best adapted to wet heathland, being tolerant of waterlogging, but can also establish itself in dry heathland. Of the three E. species it has the widest ecological range. Calluna is tolerant of both wet and dry conditions and has a wide ecological range. E. cinerea is typical of dry- and E. tetralix of wet heathland. Although both species did best in moist aerated soil in experimental cultures, neither is abundant in mesophilic heaths where E. ciliaris is dominant. One explanation may be competition for aerial space. E. cinerea and E. tetralix both have an upright growth, whereas E. ciliaris rapidly adopts a straggling bushy habit, with long rooting branches. E. ciliaris thus establishes large interpenetrating clumps. With increasing dryness E. ciliaris disappears and may be replaced by E. cinerea and, with increasing wetness and especially waterlogging, E. tetralix will take over. 相似文献
6.
A conventional balance study with 48 male weanling rats was conducted to determine true absorption and endogenous fecal excretion
of manganese (Mn) in relation to dietary Mn supply, following the procedures of a previously adapted isotope dilution technique.
After 10 d on a diet with 1.5 ppm Mn, eight animals each were assigned to diets containing 1.5, 4.5, 11.2, 35, 65, or 100
ppm Mn on a dry-matter basis. Three days later, each rat was given an intramuscular54Mn injection and kept on treatment for a balance period of 16 d.
Apparent Mn absorption assessed for the final 8 d, averaged 8.6 μg/d without significant treatment effects, although Mn intake
ranged from 18.6 to 1200 μg/d, in direct relation to dietary Mn concentrations. Mean fecal excretion of endogenous Mn for
the six treatments was 0.9, 2.7, 7.4, 11.0, 16.3, and 17.7 μg/d, respectively. These values delineate the rates to which true
absorption exceeded apparent rates. True absorption, as percent of Mn intake, averaged 28.7, 15.9, 11.7, 6.1, 3.4, and 2.0,
respectively, as compared with mean values of 23.9, 10.9, 6.2, 3.4, 1.2, and 0.5 for percent apparent absorption. It was concluded
that both true absorption and endogenous fecal excretion markedly responded to Mn nutrition and that the reduction in the
efficiency of true absorption was quantitatively the most significant homeostatic response for maintaining stable Mn concentrations
in body tissues. 相似文献
7.
白鹇距长与年龄的关系 总被引:5,自引:0,他引:5
注意到白鹧雄鸟距长在一定时期内随年龄增长的事实,本文根据相邻2年同一月龄之间有12个月的间隔,距长数据除有较为集中外一定又有组间明显差别的特点,推测估计部分标本之年龄,加上确知年龄的部分标本,共测定89个个体120个距长样本数据,得到距长随年(月)龄增长的关系式:SL=am/1+bm,用此式可以实测距长初步估计野外采集到的白鹇个体的年龄 相似文献
8.
Root,shoot and soil parameters required for process-oriented models of crop growth limited by water or nutrients 总被引:2,自引:0,他引:2
A review is given of the prospects for using process-oriented models of water and nutrient uptake in improving integrated agriculture. Government-imposed restrictions on the use of external inputs will increase the likelihood of (temporary) nutrient or water stress in crop production in NW Europe and thus a better understanding is required of shoot-root-soil interactions than presently available. In modelling nutrient and water uptake, three approaches are possible: 1) models-without-roots, based on empirically derived efficiency ratios for uptake of available resources, 2) models evaluating the uptake potential of root systems as actually found in the field and 3) models which also aim at a prediction of root development as influenced by interactions with environmental factors. For the second type of models the major underlying processes are known and research can concentrate on model refinement on the one hand and practical application on the other. The main parameters required for such models are discussed and examples are given of practical applications. For the third type of models quantification of processes known only qualitatively is urgently needed. 相似文献
9.
10.
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