DISTRIBUTION OF 32P BETWEEN ROOTS AND TOPS OF WHITE CLOVER: EFFECT OF MYCORRHIZAL FUNGI AND PLACEMENT DISTANCE FROM THE ROOTS

In a greenhouse experiment, the effects of Glomus intraradices and indigenous mycorrhizal isolates from soils under plow and no-till treatments on the uptake of 32 P placed at 1, 2.5 and 4 cm from the roots of white clover (Trifolium repens ) in 23, 37 or 46 days after planting were compared.Spores of the indigenous fungi were mostly a mixture of Glomus mossea, G. clarum, G. caledonium and G. claroideum . The colonization of the roots with regard to hyphae, vesicle or arbuscules was significantly different among fungi. Uptake of 32 P from different distances from the roots was strongly dependent on the mycorrhizal isolate used and the plant-symbiont age. Indigenous fungi were more effective in translocating 32 P from short distances compared with G. intraradices as measured in the plants . At the age of 46 days, for example, fungi from no-till and plowed plots transported 8-10 times more 32 P to the plants as compared with G. intraradices , when 32 P was placed at 1-cm distance from the roots. These differences, however, disappeared when 32 P was placed at 2.5 or 4 cm from the roots. As the plant-symbiont grew older, relatively more 32 P was translocated to the tops and the differences between fungi in this respect became more pronounced. In 21-, 37- and 46-day-old plants, for example, and when 32 P was placed 1 cm from the root surface, 18, 21 and 56%, respectively, of the absorbed 32 P was translocated to the tops in plants inoculated with fungi from plowed fields. Progressively lesser amounts of total absorbed 32 P were translocated to the tops as 32 P was placed farther away from the roots. For example in 46 days after planting 51, 30 and 11% of total absorbed 32 P was translocated to the tops when 32 P was placed at 1, 2.5 and 4 cm from the roots, respectively, white clovers being inoculated with fungi from no-till soil. It is concluded that the native mycorrhizal fungi , after a long period of different tillage practices, may have different effects on the partitioning of absorbed phosphorus within white clover.