THE UPTAKE OF PHOSPHATE BY EXCISED MYCORRHIZAL ROOTS OF THE BEECH

Abstract

Summary The temperature coefficients of phosphate absorption by beech mycorrhizas for temperature intervals below 20°C. were found to be above 2 regardless of the external concentration applied. Similar Q1o values were obtained for their constituent fungal and host tissues when exposed separately to phosphate solutions. The proportion of absorbed phosphate passing to the host through the fungal sheath was unaffected by temperature in very high or very low phosphate concentrations and the Q1o values for absorption by both tissues were of the expected magnitude. By contrast the proportion of phosphate passing to the host from intermediate concentrations (3.2 mM) was increased by low temperatures so that the estimates of Q1o for the host were lower than expected. Similarly, the inhibitors sodium azide and iodoacetic acid diminished uptake by both fungus and host in high and low concentrations of phosphate but did not affect the amount absorbed into the host from 3.2 mM phosphate. In concentrations of 3.2 mM phosphate also, separation of the fungal and host tissue increased their absorption rates over short periods but not over long periods of time. In the discussion, these results are considered together with previous experiments and it is concluded that in ecologically probable conditions phosphate passes to the host through the living hyphae of the sheath.