THE EFFECTS OF PHOSPHOROUS FERTILIZATION ON THE MYCORRHIZAL COLONIZATION OF NATIVE FORAGE GRASSES IN THE PAMPA BIOME

Resumo

Most of natural grasslands of Southern Brazil have low availability of soil phosphorus (P), and under such conditions, the association with arbuscular mycorrhizae is an adaptation to the nutrient supply. However, one of the alternatives to improve the productivity of these grasslands is P fertilization, which can alter mycorrhizal colonization. This study aimed to evaluate the effect of fertilization on mycorrhizal colonization and to characterize the mycorrhizal colonization of native grass species of different growth rate. Treatments consisted of (i) 50 mg kg-1 of P (+ P); and (ii) a control without addition of P (-P). The grasses used in the experiment were Axonopus affinis and Paspalum notatum (fast growing species), and Andropogon lateralis and Aristida laevis (slow growing species). The plant species were planted in pots with 5 kg of soil and arranged in a randomized block design with four replications. For the fast growing species (A. affinis and P. notatum), the addition of P reduced mycorrhizal colonization by an average of 55%. In relation to slow-growing species (A. lateral and A. laevis), -P had a similar mycorrhizal colonization to that of +P. Spore production was higher in slow growing species compared to fast growing species, regardless of treatments. These results indicate the key role slow growing species have in this environment. Therefore, even if fertilization reduces the colonization in the root system of fast-growing species, slow-growing species allow arbuscular mycorrhizal fungi to remain present in this environment. This type of characteristic becomes important for the coexistence of the species in natural grasslands.