摘要:

Biomass and productivity of the herb layer in a forest ecosystem. — Biomass and productivity of the overground parts of the herbs in a forest ecosystem have been estimated by means of indirect methods of measurement.Methods— In an area of 20 × 25 m2where all trees had been inoculated with Cs-137 three years before, a set of sample plots was established (figs. 1–6) where a series of measurements were made: field measurements included number of individuals, height and cover estimates for each species in the plot. All overground material was then collected, oven-dried, weighed and counted for radioactivity separately for each species. The same procedure was repeated three times at 40 day intervals, from May through to August. Dry weight and field estimates were correlated for all species (or genera) of which 10 or more data were available, using a thoroughly empirical procedure. The resulting correlations (Table I) permit the drawing of a diagram for each species (Figs. 8–21), where individual correlated points, the least square line (i.e. the regression line), the confidence interval P0.05for individual measurements and the confidence interval P0.05for the line as a whole are plotted. Such diagrams permit the prediction, with a known degree of accuracy, of the dry weight of any given plant or population of these species on the basis of field estimates. A discussion of the models of transformation applied to the original independent variable(s) to obtain the correlated variablex(Table I, col. 5) demonstrates a logical connection between the transformation required and the habitus of the various species, because direction of growth, density of leaves and stems etc. condition the way in which the basic parameters (cover and height, i.e. surfaces and lengths, or their product, i.e. volume) must be treated in order to obtain a distribution which is linear with respect to that of the biomass. From these models it can now be foreseen which transformation would be required for any plant species on the basis of its habitus, thus reducing trials, errors and waste of time to a minimum. The correlation does not seem to depend on the season. It must be established for individual species or genera: a more general correlation covering all species of a given type of vegetation and having a reasonable degree of approximation does not seem to be obtainable.Biomass and Productivity Estimates— 20 rectangular plots (0.5 × 2 m) were distributed at random within the area. A circular plot (0.1 m2) with a very similar plant cover was then located very close to each one of the rectangular plots (giving a total of 20 circular plots). Periodic field measurements were made on both types of plot. After the last measurement (mid August) the small plots were hand clipped, the plant material separated by species, oven-dried, weighed and counted for radioactivity. An analysis of the standard error of the d.w. estimates demonstrates that: a) circular 0.1 m2plots give more accurate estimates than the same number of larger plots, the estimation also being more rapid; b) indirect estimation (using the correlations previously discussed) does not involve a significantly larger error than direct measurement performed on the same plots. Number of plots was checked with empirical tests after Greig-Smith (Fig. 22) and after Milner and Elfyn-Hughes: 20 plots appear to constitute a sufficiently broad basis for this type of vegetation. After testing the significance of the correlations and the significance of the sampling method, the regression equations have been applied to the field data to estimate the biomass of each species (Table II). Only seven species account for as much as 95% of the total biomass, most of these reaching their maximum weight in the late summer, as does therefore the total biomass of the stand. The sum of highest weights reached by individual species (46.5 g/m2) does not very much exceed the August biomass (45.2 g/m2). From these data production and productivity can be calculated (Table III). Overground productivity decreases steadily during the growing season both because of the diminishing light intensity in the understory of the forest and because of translocation movements from reserve organs (prevailingly upwards during the spring and downward in the late summer). Use of radio-isotopes permits the identification of such translocation movements. These experiments were conducted three years after the trees had been inoculated with Cs-137. The soil was abundantly contaminated, mainly due to diffusion of Cesium from the roots of the trees and to leaf-fall from the canopies. Highest radioactivity ratios (Table IV) were found in the evergreen herbs, which were contaminated from the falling leaves of the year before, and in the geophytes during their period of growth from the reserve organ. Growth from photosynthesis, instead, seems to be correlated with a decrease in radioactivity: in the period after May radioactivity per unit area decreases in spite of the increase in biomass. Estimated biomass equals about 1/5 of the canopy green biomass in the same stand, about 1/5 of the chlorophyllian tissues of the ecosystem appearing to be located in the herb layer. A comparison with other ecosystems is given in Table V. A theoretical primary productivity Pp= QIϵc = 0.18 g/m2/day may be predicted on the basis of the following approximate figures: total radiation at Oak Ridge, Tennessee, Q = 3750 Kcal/m2/day; penetration of the radiation to the forest undercover, I ≈ 0.01; efficiency in radiation utilization, ϵ ≈ 0.02; calorie value of herbaceous plants, c ≈ 4 Kcal/g. Our estimated value of 0.11 g (which does not include underground productivity) seems to approximate satisfactorily with this theoretical value.

ISSN:0017-0070    

DOI:10.1080/11263507009426702

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Research on the regeneration in Pterocladia capillacea (Gmel.) Born, et Thur. cultured in vitro. II. Light intensity and development of the erect frond. — The thallus ofPterocladia capillaceaconsists of two different portions: the erect frond and the creeping axis. The former essentially assimilative and reproductive function while the latter exerts the function of perennation, attachement and vegetative propagation of the alga. As previously shown, both apical and intercalary segments, in culture, grow apically and generate adventitious buds from the cut-surfaces. If the culture are exposed to low light intensities, both the adventitious buds and the preexisting apical meristems give rise to creeping filaments. However, if the light intensity is increased over a threshold level (750–1000 lux) and the light treatment is continued for 12 hours a day, the « distal » tips, both the newly formed adventitious tips and preexistig ones, develop into regular erect fronds. On the contrary, the adventitious buds generated at the lower pole of the segment, always develop into creeping axes. These results clearly show the existence of an exact polarity in the development of the segments.

ISSN:0017-0070    

DOI:10.1080/11263507009426703

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

In vitro culture of dedifferentiated cells of Triticum vulgare Vill. — A cultural substratum allowing the formation of callus from wheat embryos excised from swollen seeds has been set up. At first it is necessary to supply the embryo with a substratum containing a large amount of Compounds having an auxinic function, as they stimulate the formation of undifferentiated cells. Secondly, in order to obtain a better growth of the colonies, it is advisable to transfer them to a medium containing a smaller quantity of auxine. The cultures can be kept for a long time, without any macroscopic differentiation of the root tips and shoot apexes, if they are monthly transferred from the medium rich in auxine to the medium poor in auxine alternatively. If the cultures are always transplanted on the substratum poor in auxine, many root tips and a few shoot apexes can be easily differentiated. Explants made from blocks of cells taken from the mother-colony and placed on the substratum rich in auxine at first, and then on the substratum poor in auxine, have grown well, and also the growth of explants made from these subcultures has proved satisfactory. If we examine, from the histological point of view, 3–4 month old cultures grown on the medium poor in auxines, we can notice a remarkable heterogeneity in the types of the cells they are made of. We can clearly see groups of meristematic cells in direct contact with portions made of proparenchymas, and zones made of provascular and vascular cells are present as well. In the most peripheral portions of the cultures the cells show extremely regressed characteristics, like the desquamating cells of the root cap. The groups of meristematic cells, without any apparent order, often organize themselves so as to form primordia of root tips and, more seldom, formations similar to shoot apexes appear. In the former, we can notice a rather regular Organization, only the quiescent center is not clearly evident; on the contrary, in the latter we can notice more irregularity, which is probably due to unbalance in the normal relations of primordium estivation.

ISSN:0017-0070    

DOI:10.1080/11263507009426704

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The Genus Allium in Italy: I. Allium pendulinum Ten. and Allium triquetrum L. — Karyological and ecological-phytogeographic studies onAllium triquetrumL. andA. pendulinumTen. have been carried out. There is clear evidence that the two species are distinct and belong to different genomatic series.A. pendulinumTen. is a palaeogenic diploid, whose relatively symmetric karyotype is:

ISSN:0017-0070    

DOI:10.1080/11263507009426705

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Crystalline inclusions in Cycads root nodules. — The crystalline inclusions observed, under both the light and the electron microscope, in root nodules of some Cycads (Macrozamia communisandEncephalartos altenstenii) are described.

ISSN:0017-0070    

DOI:10.1080/11263507009426706

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue

ISSN:0017-0070    

DOI:10.1080/11263507009426701

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor