Comparison of two test systems for measuring plant phosphorus uptake via arbuscular mycorrhizal fungi

Plant phosphorus uptake via external hyphae of arbuscular mycorrhizal fungi has been measured using compartmented systems where a hyphal compartment i s separated from a rooting compartment by a fine mesh. By labelling the soi l within the hyphal compartment with a radioactive phosphorus (P) isotope, hyphal uptake of P into the plant can be traced. The objective of this grow th chamber study was to test two hyphal compartments of different design wi th respect to their suitabilities for measurement of hyphal P uptake. One h yphal compartment was simply a nylon mesh bag filled with P-32-labelled soi l. The labelled soil in the other hyphal compartment was completely surroun ded by an 8-10 mm layer of unlabelled soil that served as a buffer zone. My corrhizal and non-mycorrhizal subterranean clover plants were grown in pots with a centrally positioned hyphal compartment. Uptake of radioactive P by non-mycorrhizal control plants was 25% of that by mycorrhizal plants with the mesh bag but only 3% when including the buffer zone. Based on this good control of non-mycorrhizal P uptake from within the hyphal compartment and its greater ease of handling once produced, we judged the hyphal compartme nt including a buffer zone to be superior to the mesh bag.