Figure 6. Shoot weight, shoot/root ratio and N/P ratio as indicators of nutritional status.

Treatments were as in Figure 3, shown are the values of the final time point (48 days after inoculation). Columns represent the average of three biological replicates, error bars represent standard deviations. Asterisks indicate significant differences between mycorrhizal and non-mycorrhizal plants (white vs. black columns), crosses indicate significant differences between the non-mycorrhizal nutrient treatments vs. the non-mycorrhizal water treatment (i.e. between the different white columns). (a) Shoot weight of plants grown with R. irregularis (black column) or without (white columns) under different nutritional conditions. (b) Shoot/root ratio of plants inoculated with R. irregularis (black columns) or without (white columns) under various nutritional conditions. A ratio of 3.5–4 indicates that plants are well supplied with mineral nutrients, whereas a ratio around 2 indicates that plants are starved and allocate relatively large amounts of resources to the root system to compensate nutritional deficits. (c) N/P ratio of the same plants as in (a),(b). In the absence of exogenous P_i supply, mycorrhizal plants (black columns) exhibited lower N/P ratios than non-mycorrhizal controls, reflecting increased mycorrhizal P_i supply. Administration of 5 mM KH₂PO₄ reduced N/P ratio even stronger than AM, in particular if only P_i was supplied.