Distribution of 32P between Roots and Tops of White Clover: Effect of Mycorrhizal Fungi and Placement Distance from the Roots

Abstract

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 32P 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 32P 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 32P 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 32P to the plants as compared with G. intraradices, when32P was placed at 1-cm distance from the roots. These differences, however, disappeared when 32P was placed at 2.5 or 4 cm from the roots. As the plant-symbiont grew older, relatively more 32P 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 32P was placed 1 cm from the root surface, 18, 21 and 56%, respectively, of the absorbed 32P was translocated to the tops in plants inoculated with fungi from plowed fields. Progressively lesser amounts of total absorbed 32P were translocated to the tops as 32P was placed farther away from the roots. For example in 46 days after planting 51, 30 and 11% of total absorbed 32P was translocated to the tops when 32P 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