Uso e propriedades do solo : efeitos nas micorrizas arbusculares

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

Arbuscular mycorrhizal fungi (AMF) are important components of ecosystems, because they are associate to plants and they increase phosphorus absorption, being important for studding the effects of converting native areas in to pasture or cultivation of the AMF in areas of âCaatingaâ and of Atlantic forest, and to evaluate the capacity of mycorrhizal plants in absorbing P in soils with increasing capacity of P fixation in competitive situation with heterotrophic biota for P of the soil. This study examined the conversion effect in use from areas on the quality and quantity of arbuscular mycorrhizal fungi propagules (AMF). Soil samples were collected from ten sites having cultivated areas adjacent under native vegetation at the same slope position at two depths 0-7.5 and 7.5-15 cm, on transects at four sampling points 20-30 m between each one, totalizing 160 samples (10 sites x 2 soil uses x 2 depths x 4 sampling points). Areas were separated in to four groups based on management history and soil erosion: Undisturbed Dry Forest (UDF), Disturbed Dry Forest (DDF), Preserved-Cultivated (PC) and Degraded-Cultivated (DC). The roots (<2 mm) were stained with trypan blue and percentage of AMF colonization was assessed. The AMF spores were separated from soil by wet sieving, incubated on solution tetrazolium chloride (INT) (2,3,5-thiphenyltetrazolium) and were counted the viable (reddish stained spores in INT) and unviable spores (remained unstained in INT). The soil was analyzed with relationship to the availability of P and the amount of spores of AMF viable, using iodonitrotetrazÃlio chloride (INT), and of the unviable. The viable and unviable spores quantity under areas was greater at depth 0-7.5 cm. The viable spores density varied from 1.4 to 6.8 spores/50 g of soil and unviable spores from 91.4 to 226 spores/50 g of soil. At the depth of 0- 7.5 cm, the DDF area had greater density of viable spores than in the PC area, and not differ in the UDF and DC areas, while at a depth of 7.5-15 cm the spore density not differ among the soil uses. The unviable spores density was greater on PC, independently from depth. The P resin seems to have influence on root colonization in cultivated areas in 0-7.5 cm layer. The fine roots were collected, colored with trypan blue and analyzed the colonization for the AMF. The viable and unviable spores number in the areas was greater at the depth of 0-7.5 cm than at 7.5-15 cm. The viable spores density in the samples varied from 1.4 to 6.8 spores/50 soil g and unviable spores from 91 to 226 spores/50 soil g. The change intensity of the use of the soil had little effect on the viable spores number, while the increase in depth promoted decrease in the number of spores. The colonization to give roots for AMF in the areas cultivated with concentrations of Presin <1 mg kg-1 at soil were smaller than in areas with P-resin >1 mg kg-1, at the depth 0-7.5 cm, what perhaps indicates a critical concentration of P in the soil for making the symbiosis possible. To study the effect of the conversion of an area of Atlantic forest in to pasture (Brachiaria decumbens Stapf) and in reforestation with Mimosa caesalpiniifolia Benth on the diversity of species and the propagules AMF, seven soil samples were removed (pseudorepetitions), from a layer of 0-15 cm in depth, totaling 21 samples (3 places with different uses x 7 sampling points). The leaf litter, that was on the area, was collected could be taked the soil samples. The roots in the soil and leaf litter were prepared for colonization verification of AMF. AMF spores were extracted from the soil and counted, the viable (colored for INT), unviable and mummified. In the three areas 28 AMF species were found, distributed in the genera Archaeospora (1), Acaulospora (8), Entrophospora (1), Glomus (14), Gigaspora (1) and Scutellospora (3). The pasture area had larger species richness (22 species), followed by the M. caesalpiniifolia area (14) and for the forest area (11). Archaeospora leptoticha, Glomus sp1, G. etunicatum, G. macrocarpum and G. microaggregatum occurred in all the areas. In the with forest and with M. caesalpiniifolia areas the species Glomus invermaium and G. macrocarpum were more frequent, while in the pasture the most frequent species were Entrophospora colombiana, Glomus diaphanum and G. macrocarpum. In the forest area there was one AMF species with exclusive occurrence, in the M. caesalpiniifolia there were two species and in the pasture there were 11 species. The areas of native forest and M. caesalpiniifolia presented similar mycorrhizal infectivity, and the large proportion of colonized roots looked to be the main source of propagules in these places. In the area with pasture the great amount of viable spores can be the most important factor for the maintenance of the mycorrhizal infectivity. The effect of the AMF was studied for increase the phosphorus (P) absorption for plants in soils with increasing capacity of fixation of P, and also in the competition for soil P between plants and the heterotrophic biota, activated by the addition of sources of carbon. Two experiments were mounted, with in random design, in vases with two concentric compartments, the internal compartment containing washed sand and the external soil marked with the isotope radioactive 32P. The internal compartment of the vases contained lateral openings, in which nylon screens were glued: or with mesh 40 μm, that allows the hyphae passage and not the roots, or mesh with 1 mm, for the which the hyphae and roots pass. The factorial arrangement of the first experiment was of 3 soils (high, medium and low P fixation) Ã 2 mesh (40 μm and 1 mm) Ã 4 repetitions. In the second experiment the arrangement was of 2 soils (high and low P fixation) Ã 2 sources of C (cellulose and straw) Ã 2 mesh (40 μm and 1 mm) Ã 3 repetitions. In the internal compartment AMF spores and Brachiaria decumbens seedlings were placed. The experiments had duration of five weeks. The dry mass was evaluated, the content of P and the specific activity of P in the plants. The dry mass, the P content and the specific activity decreased with the increase of the capacity of P fixation for the soil. The variation in the specific activity suggests different levels of isotopic dilution in each soil. The AMF contribution for dry mass and P content was greater with the increase of the P fixation for the soil. The carbon sources addition to the soil with low P fixation produced decrease in the dry mass and in the P content in the plants. The cellulose had a more depressive effect than straw. The variation in the specific activity indicated that P available for the plants was from different origins in the treatment with straw and cellulose. In the high fixation soil the cellulose addition produced decrease of dry mass, P content and specific activity, independently of the mesh. The largest values of specific activity found in the plants with free access to the soil (mesh 1 mm) can be due to the most immediate exploration of the soil for the plants with restricted access (40 μm).

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micorrizas arbusculares engenharia nuclear solo propriedade uso

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