Micorrizas arbusculares e assimilação de nutrientes em uma meso-escala na região amazônica

Abstract

Several ecological processes have been shown the heterogeneity of the Amazonian ecosystem, reflecting variation in soil fertility, length of the dry season among other parameters. Thus wide scale studies allow a global approach on the functioning of the Amazon. The contribution of the arbuscular mycorrhiza (AM) in these processes has not been well elucidated yet and became the reason for this study which main objectives were: (i) To evaluate the spatial variation, in a mesoscale, the relationship between the carbon (C), phosphorus (P), and nitrogen (N) contents and other minor nutrients whit the colonization by arbuscular mycorrhiza fungi (AMF) in terra firme forest in three Amazonian countries; (ii) To estimate the carbon (C), phosphorus (P), and nitrogen (N) contents and other minor nutrients in the roots of three individual belonging to three families common to all those forests; (iii) to observe the influence of the soil properties on the degree of mycorrhizal colonization and the production of mycorrhizal spores in those Amazonian forest. The study was carried out in an east-west transect with 1500 km in length, crossing three Amazonian countries, Brazil (Reserve Cueiras), Colombia (Station Zafire), and Peruvian (Station Jenaro Herrera). 180 samples of roots and rhizospheric soils were collected in 60 tree individuals belonging to three families- Lecythidaceae, Sapotaceae and Burseraceaefound in each of the three sites. Root samples were processed and chemically analyzed. Soil properties were also determined for nutrient and physical status. Rates of mycorrhizal colonization in the roots and extraction ands counting of AMF spores in the soil samples were made. Despite de geographical variation encompass 1500 km in the east-west direction, the soils in the three sites were still classified as acidic and low in fertility. Soils at Reserve Cueiras were the most clayey, nutrient-poor and lowest in number of AMF spores. By the nutrient in the roots, individuals in each tree family (Lecythidaceae, Sapotaceae e Burseraceae) showed differences in the absorption of the main nutrients (P, C, N) between each site and also for other nutrients (K, Ca, Mg). However no differences were observed in the mycorrhizal colonization rates neither between families nor between sites, with laver rates (average 36%) in three sites. Moreover, the relationship between soil and plants for the main nutrients were not affected by the rate of mycorrhizal in any of the sites. Soil properties showed that mycorrhizal association with plant roots is a widespread strategies used by the arboreal vegetation in the P absorption. Soils at the Station Zafire and Jenaro Herrera showed high Al content, a limiting factor to plant productivity on acid soils. However, the mycorrhizal association seems to buffer the damage caused by the excesses of Al in the soils. Similarly, the tolerance of the plants to the acid soils of the region, common at the three sites studies. Finally, the results in this study allow the conclusion that though the scale and geographical positioning used vary in some soil properties at the various sites they were not enough drastic for plants to alter the use of the AM as a strategy for nutrient acquisition.