Fungos micorrízicos arbusculares em interação com gênero Urochloa: simbiose e influência na estabilidade de agregados do solo

Abstract

Arbuscular mycorrhizal fungi (AMF) play important roles for plants and soil, such as aggregation and physical structuring. However, the effect of AMF inoculation on soil aggregation has not yet been fully elucidated. In this context, the objective of this research was to evaluate the inoculation of different AMF species in Urochloa plants on the multiplication of these AMF and their influence on the formation and stability of the aggregates in the soil. The research was conducted in three experiments, two in greenhouse at the Department of Soil Science (DCS)/Federal University of Lavras (UFLA), using five AMF (Acaulospora colombiana, Acaulospora longula, Acaulospora morrowiae, Paraglomus occultum and Gigaspora margarita) associated with Urochloa brizantha (A. Rich.) Stapf. And in the field at the Experimental Station of Pastures and Forages/National Institute of Agricultural Sciences (INCA), Cuba, inoculating three FMAs (Funneliformis mosseae, Glomus cubense and Rhizophagus intraradices) in hybrid Urochloa (CIAT BR 02/1752 "Cayman") in a Ferruginous Nodular Gleysol. In the first greenhouse study mycorrhizal multiplication and colonization was evaluated over time. In the second study and in the field, the influence of inoculation on the stability of soil aggregates (dry and immersed in water), soil aggregates stability index, quantification of extrarradicular mycelium and glomalinrelated soil protein production in the samples of the soil and within the classes of the aggregates (the latter only in greenhouse). The analyzes were carried out in the DCS/UFLA and INCA laboratories, for greenhouse and field experiments, respectively. In the first study, it was observed a higher mycorrhizal colonization in less time of cultivation for the A . colombiana species, which reached the stabilization at 76 days and showed a larger number of spores at 120 days. On the other hand, P. occultum and G. margarita did not reach the maximum mycorrhizal colonization and density of spores at 120 days, indicating that a longer period for multiplication of these AMFs associated with U. brizantha was necessary. For glomalin there was a larger increase for inoculation with A. colombiana, A. longula and P. occultum at 120 days of cultivation. In the second study, the inoculation with A. colombiana presented a larger extrarradicular mycelium length and Ø of the aggregates immersed in water, when compared to the treatment without inoculation. The highest levels of glomalin were observed for inoculation with A. colombiana and A. morrowiae in the classes of aggregates with Ø> 2.0mm and Ø <0.105mm, when compared to the treatment without inoculation. In the field study, it was verified a higher stability of the dry aggregates at 140 and 876 days of cultivation, when compared to the immersed ones in water, having influence of the inoculation only at 876 days. Indicating lower stability of water immersed aggregates and the influence of "kinetic energy" on the soil structure. The stability of the aggregates was favored by the cumulative (cumulative) capacity of the glomalin and the length of the extraradicular mycelia (at 876 days), due to the greater entanglement of the soil particles. The roots of U. brizantha and B. hybrids associated to inoculation had an important effect on the stability index of soil aggregates, in a greenhouse at 180 days and in the field at 876 days (with emphasis on G. cubense). Which also had a greater competitive potential with the native FMAs over time. These results showed the importance of knowing the interactions of host AMFs in order to optimize the symbiosis and its benefits, or even to manage native AMFs for formation and stability of the soil physical structure.