NO SIGNIFICANT TRANSFER OF N AND P FROM PUERARIA-PHASEOLOIDES TO HEVEA-BRASILIENSIS VIA HYPHAL LINKS OF ARBUSCULAR MYCORRHIZA

The possible role of arbuscular mycorrhizal fungi in the transfer of n itrogen and phosphorus from Pueraria phaseoloides (donor) to Hevea bra siliensis (receiver) was examined. P. phaseoloides is used as a cover crop in rubber tree (H. brasiliensis) plantations. Roots of donor and receiver plants were separated by a root-free soil layer in a three co mpartment PVC container. Inoculum of Glomus clarum was applied only to P. phaseoloides, and H. brasiliensis was colonized solely via hyphae spreading from the donor. A proportion of the donor roots grew into a labelling compartment, which received four split applications of N-15 and P-32 from 12 to 15 weeks after planting. After 16 weeks donor shoo ts were then left intact, shaded or removed and the isotope content of donor and receiver plants measured after a further 4 weeks growth. Th e recovery of labelled N in receiver plants was small and averaged 0.0 5 and 0.03% for mycorrhizal and non-mycorrhizal H. brasiliensis. The e stimated transfer of N and P from P. phaseoloides to H. brasiliensis w as not affected by mycorrhizas despite the high degree of root coloniz ation in both species. The percentage of total legume N transferred to H. brasiliensis was estimated to be 0.07 and 0.05% in the intact or s haded donor plant treatments, but 0.27% when the legume shoot had been removed. This transfer corresponded to 0.15, 0.07 and 0.40% of total N in H. brasiliensis The amounts of donor P transferred were 0.8% (int act), 1.6% (shoot removed) and 0.8% (shaded) of total P. phaseoloides P. The evidence does not support a significant role of mycorrhizal lin ks in the direct nutrient transfer between plants. The transfer most l ikely occurred by indirect means via root exudation and mineralization of nutrients from legume plant residues.