Assertion : Endomycorrhiza of forest trees contribute to the efficient nutrient cycling in tropical forest ecosystems. Reason: The fungi that form endo-mycorrhizal associations with plants make nutrient ions available to them.

Step-by-step solution

The fungi of endomycorrhiza invade the cells of the root cortex, with a portion lying externally as a loose mass of hyphae in the soil. Mycorrhiza cause considerable stimulation of growth in nutrient deficient soil. The greatest stimulation occurs in the uptake of phosphates. Mycorrhiza can take up phosphate at that low concentrations at which they are unavailable to nonmycorrhizal roots.