TRANSLOCATION OF PHOSPHORUS FROM NODAL ROOTS IN 2 CONTRASTING GENOTYPES OF WHITE CLOVER (TRIFOLIUM-REPENS)

Patterns of translocation of recently-assimilated phosphorus (P) expor ted from 'young' source roots (located 3-4 nodes from the stolon apex) and 'old' source roots (located near the base of the stolon) on the p rimary stolon of clonal plants of the forage legume white clover (Trif olium repens L.) were determined using P-32. Plants of a small-leaved genotype and of a large-leaved genotype were grown in sand culture at two notionally limiting or near-limiting rates of P supply and one non -limiting rate of supply. The small-leaved genotype showed little resp onse in growth rate to the full range of P treatments whereas growth o f the large-leaved genotype at the non-limiting rate of P supply was 2 .4 times greater than at the two low rates of P supply. Source roots o f both genotypes exported only 26-30% of the P they acquired to the sh oot within 24 h when P supply was limited whereas at the high-P rate 5 4% of recently-assimilated P was exported. Patterns of translocation o f exported P to specific sinks differed little between the genotypes a nd the P treatments; branches were the main sink, accounting for nearl y 80% of the estimated amounts of P (mug day-1) exported from young an d old roots combined. Translocation patterns from individual roots wer e determined largely by the modular structure of plants and by the loc ation of the root relative to the major sinks, and were therefore cons istent with the same source-sink principles which govern carbohydrate translocation in clonally-growing species. There were strong suggestio ns that storage of P in stolons and roots played a much greater role i n the growth of the small-leaved plants than of the large-leaved plant s.