African Crop Science Journal African Crop Science Society ISSN: 1021-9730 EISSN: 2072-6589 Vol. 5, Num. 4, 1997, pp. 413-418

SHORT COMMUNICATION

STUDIES ON THE ROOT SYSTEMS OF Bixa orellana

I. Macdonald

Department of Botany, Faculty of Science, University of Benin, P.M.B. 1154, Benin-City, Edo State, Nigeria

(Received 18 January, 1994; accepted 28 July, 1997)

Code Number:CS97046
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ABSTRACT

The root morphology of Bixa orellana L. is typical of a dicot root system with a central tap root holding several laterals. The effect of nutrient status of soil, collected from six states of Nigeria, on Bixa orellana root production was studied. It was observed that soil with higher fertility had higher dry weight matter yield and greater production of roots. Nitrogen levels in the rooting medium influenced root production more than did K and P. However, N, K and P had no influence on the elongation of the tap root.

Key Words: Bixa, nutrients, root extension, Southern Nigeria

Resume

La morphologie racinaire de Bixa orellana L. est typique au systeme radiculaire des dicotyledons caracterise par une racine principale portant plusieurs racines laterales. L'effet de la composition minerale du sol recolte dans six etats du Nigeria, sur la production des racines de Bixa orellana a fait l'objet d'une etude. On a observe que le sol ayant une plus grande fertilite avait aussi un rendement en poids de matiere seche plus eleve et une plus grande production des racines. Les teneurs en azote dans la zone racinaire influencait la production des racines plus que celles de potassium et de phosphore. Cependant, N, K et P n'ont presente aucune influence sur l'elongation de la racine principale.

Mots Cles: Bixa, elements mineraux, extension des racines, sud du Nigeria

INTRODUCTION

When the supply of nutrients within the soil is non-uniform, plant roots are often found to grow preferentially towards those regions of the soil which contain favourably high nutrient concentrations (Passioura and Wetselaar, 1972; Jordan and Escalante, 1980; Sattelmacher et al., 1993; McMichael and Quisenberry, 1993). Nutrient supply has a pronounced influence on both the size and morphology of the root system. This effect depends mainly on nutrient concentration and environmental conditions, such as light intensity, pH, ionic balance, e.t.c. (Drew, 1975; Drew and Saker, 1978; McMichael and Quisenberry, 1993; Sattelmacher et al., 1993)

Russel (1987) observed that when lateral roots of Pisum sativum grew in contact with regions saturated with different inorganic ions, nitrates and phosphates were the most effective in stimulating the initiation of roots. Aber et al. (1985) reported that increasing availability of N appears to encourage higher turnover of fine roots in comparison to those ecosystems where nitrate level are low.

The present study, which is part of a series of research work on Bixa orellana, aimed at investigating the influence of nutrient status in soils of southern Nigeria, on the root system of Bixa orellana.

MATERIALS AND METHODS

A greenhouse study was conducted on the root system of Bixa orellana, using six soils collected from Warri, Ikorodu, Benin City, Ore 1, Ore 2, Ijebu Ode, Shagamu, Ibadan 1 and Ibadan 2, located in the southern part of Nigeria. Samples were collected, bulked and sieved using a 4.00 mm sieve. Sieved soil was then placed in a wooden tray of 75 cm x 50 cm x 45 cm.

The chemical and physical properties of the soil viz.: pH, total nitrogen, potassium and soil texture were determined using methods outlined by Bates (1954), Murphy and Riley (1962), Bonyones, (1951) and Tel (1984). Results of the analysis are shown in Table 1.

Bixa orellana seed used in this study were collected from the Air Force Base Compound, Ikeja, Lagos, Nigeria. Ripe capsules were collected, and the seeds removed and sun-dried for seven days. They were then stored in air-tight screw cap glass vials. Three hundred seeds were sown in each wooden tray containing different soils. Watering was done daily using distilled water. The study lasted twelve weeks and was laid out a in completely randomised design with five replications.

Root measurements were taken, using methods outlined by Pandey et al. (1968), Newman (1968), Drew et al. (1973) and Welbank et al. (1974). Roots impression was done by staining 100 roots from each tray, of well developed seedlings (visually determined) of Bixa orellana using dark ink on white background graph paper (1 cm^2). Average total surface area was recorded using a 1 cm^2 graph paper. Average total length of tap roots, root axis and lateral were recorded using a thread and a ruler. Fifty plants were carefully removed from the soil and weighed using a sensitive weighing balance, to determine fresh weight. Fifty other plants were carefully removed and oven dried at 80 C until a constant weigh was achieved to determine dry weight. Data were subjected to analysis of variance and mean seperation using LSD (P=0.05) (Steel and Torrie, 1980).

RESULTS AND DISCUSSION

Chemical and physical characterisation of the soils from the six location is summarised in Table 1. The results showed a variation in soil pH from 6.20 in soil S3, S5 and S6, soil texture also varied, from sand to loamy sand, sandy loam and sandy clay with different values for N, K, P availability.

Considerable modification of dry matter distribution, axis and lateral root production occurred in Bixa orellana resulting from the variation in concentration of N, K and P within the rooting zone (Fig. 1 and Fig. 2). The present study showed a significantly positive correlation between the N in the rooting medium to the P and K. This observation agrees with Black (1968) who observed that the supply of N in the growth medium is a major factor controlling the distribution of dry matter in plants.

Plants grown in media with high concentration of N, weighed more than those with lower N supplies (Fig. 1). For instance, soil S2 with 0.16%N, resulted in dry weight of 0.133 g, while S9 with 0.09% N yielded only 0.098 g (Fig.1). The dry weight of a plant is expected to correlate closely with the nutritional status of the plant, since dry matter production depends on the rates of photosynthesis and respiration.

The nutritional effect of N, K, and P on root surface area indicate clearly that the concentrations of these elements affected the development of roots directly (Fig. 3). Effects on production in the present study were more controlled by N and K than P. However, Hackett (1968) worked with different barley varieties and observed different morphological characteristics as a result of differences in nutrient levels, particularly phosphorus and potassium deficiencies.

The most striking feature of the results were the response of the root systems to natural supply of nitrogen,which affected the rate of root extension (Fig. 3). According to Weaver and Clements (1938), roots which come in contact with soil layers enriched with N, branch profusely. Inputs of excess nutrients, especially N, have a significant effect on below ground plant parts, since they affect total plant carbon allocation patterns to biomass and storage carbohydrates (Horner, 1987; Vogt et al., 1993).

In conclusion, the way in which the higher N concentration stimulates axis and lateral root initiation and subsequent extension, is of central importance in understanding the conditions under which root form is controlled by the supply of nitrogen. Moreover, all the root structural changes that occurred in Bixa orellana in response to increasing N availability gives us tools that can be used to monitor why some plant species are less competitive in occupying a site, or have reductions in biomass increment, or perhaps have increased mortality.

ACKNOWLEDGEMENT

The author wishes to acknowledge the support of Dr. Umebese of the University of Lagos, Mr. Owuama of FUTY and Late Prof. L. S. Gill of the University of Benin, Benin City, Nigeria for their contributions to this work.

REFERENCES

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Bonyones, G.J. 1951. A recalibration of hyddrometer method for making mechanical analysis of soils. Agronomy Journal 43:434-438.

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Hackett, C. 1968. A study of the root system of barley. I. Effect of nutrition on two varieties. New Phytology 67:287-299.

Horner, J. B. 1987. A Preliminary Investigation of the role of Phenolic compound in Ecosystem processes. Ph.D. Dissertation, University of New Mexico, Albuquerque.

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Russel, E. W. 1987. Root Systems. Longman. 248pp.

Sattelmacher, B., Gerendes, J., Thomas, K., Bruce, H. and Bagdady, N. H. 1993. Interaction between root growth and mineral nutrition. Environmental and Experimental Botany 33: 63-73.

Steel, R.G.D. and Torrie, J.H. 1980. Principles and procedures of Statistics. A Biometrical Approach. Second edition Mc Graw-Hill Book Co., NY 633pp.

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Vogt, E. A., Publicover, D., Bloomfield, J., Perez, J. M., Vogt, D. J. and Silver, W. L. 1993. Below ground responses as indicators of environmental change. Environmental and Experimental Botany 33:189-203.

Weaver, J. E. and Clements, F. E. 1938. Plant Ecology. 2nd Ed. McGraw-Hill, New York. 428pp.

Welbank, P., Gibb, M. J., Taylor, P. J. and Williams, E. O. 1974. Root growth of cereal crops. Report Rothamsted Experimental Station for 1973. Part 2. 266-66pp.

Copyright 1997, African Crop Science Society

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