Fungos micorrízicos arbusculares e doses de fósforo na produção de Parkia nítida (Miquel) em viveiro no sul do Amazonas

Abstract

The quality of the produced seedlings is a major factor for the success of forest stands. Arbuscular mycorrhizal fungi (AMF) form a mutualistic symbiotic association with the roots of most tropical plants and extend the exploitation area of soil, favoring the absorption of water and nutrients, especially phosphorus. Although this association is much studied, little is known about the effects of AMF inoculation on the initial development of Parkia genus plants and mainly about their phosphorus nutritional need. Therefore, the objective of this study was to evaluate the effect of the AMF inoculation in different doses of phosphorus on the initial growth of Parkia nitida. The experiment occurred at the Federal Institute of Education, Science and Technology of Amazonas - Lábrea Campus (7°15'02.9"S 64°47'05.5"W), being carried out in a completely randomized design in a 5x2 factorial scheme, with 5 treatments: 1) control treatment, without phosphorus addition; 2) with addition of 20 mg L-1 phosphorus; 3) 40 mg L-1 phosphorus; 4) 80 mg L-1 phosphorus; 5) 160 mg L-1 phosphorus. In all treatments occured the addition of mycorrhizal fungi in half of the evaluated plants, and the remaining half in each treatment did not receive the inoculation. The inoculation was done by applying 5 mL of inoculum soil (colonized roots, hyphae and spores) containing a mix of spores (70 spores/mL) of the species Acaulospora longula, Acaulospora morrowiae, Dentiscutata heterogama and Paraglomus occultum. The native arbuscular mycorrhizal fungi spores were obtained from the soil collected in a chestnut tree area (7°28'15.3"S 64°39'26.3"W) and multiplied in flowerpots with brachiaria for 8 months. The variables analyzed were the Survival Rate (TDS), height (h), lap diameter (d), Seedling Quality Index (h/d), leaflet area (ADF), leaflet number (NDF), dry mass of the aerial part (MSPA), dry mass of the root (MSR), MSPA/MSR ratio, total dry mass (MST) and Dickson Quality Index (IQD). The variables h and h/d were significant for the interaction between factors only for the treatment without inoculation. The plants presented linear increments with phosphorus doses increase, for the variables ADF, MSPA and MST. The other variables were not significant. It was not possible to determine the appropriate phosphorus dose for the production of Faveira-branca seedlings, but the aerial part of the seedlings positively responded to the increase of the phosphorus doses. Inoculation with spore mix (inoculum soil) did not show significant results in the experimental conditions as well as in the phosphorus interaction.