Peach seedlings were grown in aerated nutrient solution in small (15 cm3) or large (500 cm3) containers. Subsequently some plants were removed from the small to the large containers or were stressed by root pruning. Half the plants received a foliar spray of 6-benzylaminopurine (BAP) every 4 days. Root restriction eventually impaired growth rates and ultimately plant size. The effect of root pruning was quickly overcome by a redistribution of growth in favour of the roots. When restricted plants were transferred into large containers there was an accompanying rapid root growth and plants attained a comparable size to unrestricted plants. BAP applied to the leaves to some extent overcame the reduced growth of restricted plants, however, its major effect was on the distribution of dry matter. Restriction and BAP application, in general, reduced the levels of mineral nutrients in the leaves. It is argued that the limit set by the roots on top growth involves an internal regulation by the root, in particular the production and supply of growth substances. The evidence suggests that this is related to root morphology and must be taken into account when studying top:root inter-relationships. The experiment highlights the importance of root restriction as a technique for manipulating root growth and studying root function and its interaction with the top. Some implications of controlled root growth in the field are discussed.
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Richards et al. (1977) studied this question.