Quantitative Studies of Root Development II. Growth in the Early Stages of Development

Abstract

SummaryThe growth of the root systems of barley seedlings was measured at daily intervals for the first 2 weeks after germination. The lengths and numbers of primary and higher-order branches were recorded and relative rates of extension and multiplication together with mean extension rates were derived from the data.An earlier suggestion that root growth rates are high early in plant development but then fall to a lower level was supported by the data which also demonstrated changes in growth rate associated with the initiation of secondary and tertiary roots. A high nutrient concentration reduced root growth -both by a transient effect on germination rate and a continuing reduction in mean extension rate. Nutrient effects on branch root production were traceable to these effects on elongation of the parent root. I. INTRODUOTIONIn the previous paper in this series (May, Chapman, and Aspinall 1965) it was demonstrated that the average relative rates of both extension and multiplication of roots of plants growing in a tenfold range of nutrient concentration were the same and, moreover, essentially constant over a period of 6 weeks beginning 2 weeks after seedling emergence. There were, however, substantial differences in both numbers and lengths of roots from different nutrient concentration at the time of the first sampling. Furthermore, extrapolation of the root growth curves, both of extension and of multiplication, back towards seedling emergence indicated that the relative rates of root development must have been considerably greater in the first 2 weeks of growth than in the period under observation. These data suggested the importance of this early period of developntent in establishing the pattern of root growth.This early period of seedling root growth has been directly explored in the present investigation. The changing rate of root growth in this period and the origin of the effects of nutrient concentration have both been examined. II. EXPERIMENTAL METHODSIn general, the techniques used in the work reported in this paper were identical with those previously described (May, Chapman, and Aspinall 1965). Barley plants (cv. Piroline) were grown singly in perlite-filled cylinders (5·5 cm diameter by * Part I, Aust.

A Model of the Extension and Branching of a Seminal Root of Barley, and Its Use in Studying Relations Between Root Dimensions I. the Model

“…These expressions, albeit for a single root, explain a prominent feature of their results. May et al (1967) stated that for the whole root system, the mean extension rate declined with time, particularly over the first 4 days of growth. We show in Figure 3 and Table 3 that the magnitude of all four growth measures of a root system will tend to that of the dominant order of lateral, so it is not surprising that the mean extension rate fell in the manner reported.…”

“…Firstly, the model could be valuable for estimating data for interpolation between actual data obtained from well-spaced harvests of root material. A need for such a facility is now emerging from investigations of the nutrient uptake TABLE 3 EXPRESSIONS OF SOME GROWTH MEASURES OF THE STANDARD ROOT Expressions after May, Chapman, and Aspinall (1965) and May et al (1967) characteristics of different types of root member (e.g. Russell and Sanderson 1967;Bowen 1968, 1970;Clarkson and Sanderson 1971).…”

“…Some independent verification was obtained, however, from the experiments of May, Chapman, and Aspinall (1965) and May et al (1967) who analysed the growth of the root system of barley in terms of the four growth measures listed in Table 3. Using the symbols adopted for the model, and considering one root only, it can be shown that their growth measures are expressed by the model in the form shown in columns 3-6 of Table 3.…”

Topological scaling and plant root system architecture: developmental and functional hierarchies

“…The primary centrifugal (developmental) segment based ordering scheme (' FS') which has been applied to plant root systems is the developmental ordering scheme. This scheme has been used extensively in describing patterns of root growth (May et al, 1965(May et al, , 1967Hackett, 1968) and in modelling the growth of plant root systems (Lungley, 1973;Rose, 1983;Diggle, 1988;Pages, Jordan & Picard, 1989;Lynch & Nielsen, 1996). In this scheme, different orders reflect the hierarchical nesting of multiple growth axes in a root system (Fig.…”

Use of morphometric analysis for characterization of tobacco root growth in relation to infection byPhytophthora parasitica var.nicotianae

“…The developmental model has been used most often to describe development of root systems of various field crops grown under different fertilization regimes, light intensities, or other imposed treatments (Hackett, 1971;May et al, 1965;May et al, 1967;Rahman et al, 1975;Tennant, 1976). Bloomberg (1979aBloomberg ( , 1979b has utilized this model to quantify root system development of Douglas-fir seedlings.…”