Influence of phosphorus nutrition on mycorrhizal growth response and morphology of mycorrhizae in Lotus tenuis

Abstract

The effect of several rates of phosphorus (P) supply on the forrnatipn of mycorrhizae by indigenous fungi in Lotus tenuis was studied. A greenhouse experiment was conducted for 45 days on a P‐deficient soil fertilized with 0–160 ug P g¹ soil. The most prevailing VAM fungus that infected roots was Glomus sp, resembling Glomusfasciculatum. Adding P to me soil influenced the mycorrhizal growth response, the extent of th,e mycorrhizal infection, and the morphological characteristics of the mycorrhizal colonization in roots. Non‐mycorrhizal plants required 1.5 times more added P to obtain the same yield as mycorrhizal plants. Nevertheless, the relationship between the P concentration in shoots and the dry weight of shoots was the same for both mycorrhizal and non‐mycorrhizal plants suggesting that differences in growth reflect differences in the uptake of P rather than its utilization within the plant. The percent of root length infected (HC) and the fraction of infected roots containing arbuscules (AC) initially increased at low levels of added P, and then with further additions, they decreased. The number of entry points per unit of root length infected decreased with increasing P concentration in the shoots. The ratio between the number of entry points and hyphal and arbuscule density decreased at low P and then increased with increasing added P. Thus, the morphology of the mycorrhiza was altered by P nutrition. It was concluded that at the lower levels of added P, the low P soil status inhibited both the spread of the fungus within the root and the growth of the roots.