Root Architecture Effects on Nutrient Uptake

Abstract

Root size and architecture are considered to form a major factor in nutrient uptake efficiency of plants (Fitter, 1991). Simulation of root growth and architecture has shown that root architecture affects the volume of the soil from which nutrients can be exploited (Fitter et al, 1987; Fitter et al., 1991). Models of nutrient uptake by roots showed that architectural characteristics may affect nutrient uptake. Barber and Silberbush (1984), using an uptake simulation model, demonstrated that nutrient uptake rate is dependent on root radius, length and density. Itoh and Barber (1983) improved the agreement between actual and predicted results by including root hairs in the model. The above information indicates that root architecture may affect nutrient uptake from the rhizosphere. However, there is very little quantitative knowledge on this effect and quantitative experimental data are vague. O’Toole and Bland (1987) found that cotton genotypes showing tolerance to water stress were characterised by long lateral roots, whereas, Petrie et al. (1992) did not find any significant effect of root architecture on water uptake from soil by mono- and di-cotyledonous species that differed in root branching and density. Eghball and Maranville (1993), comparing N uptake by two varieties of corn, showed that the one with longer and thinner roots was more efficient in N uptake. The difficulties in obtaining such quantitative data are: i. monitoring and measuring root parameters in vivo, ii. discriminating between root and shoot effects, and iii. estimating relative impact of morphological and functional effects on nutrient uptake. Changes in endogenous free polyamines (putrescine, spermidine and spermine) were found to be in correlation with root formation (Friedman et al., 1982; Burtin et al., 1990). Recently it was found that application of an inhibitor of putrescine synthesis, DFMO (α-DL-di- fluoromethylornithine), caused changes in phenotype development (Burtin et al, 1991) and altered the architecture of excised root system of tobacco (Ben-Hayyim et al., 1993). Using excised root simplifies the experimental system by avoiding shoot/root interaction; the biochemical effect is exerted specifically on root architecture without affecting nutrient demand and uptake characteristics of root unit, thus enabling one to quantify the effects of architectural parameters on nutrient uptake. However, tobacco roots grow very slowly, and so, successful application of the method to fast growing roots of another species, e.g., tomato, would improve the experimental system. There has been no study of the effect of DFMO on either the nutrient uptake or the development of excised tomato roots.