Soil structure, which is defined by the arrangement of the particles and the porous space forming aggregates, is one of the most important properties of the soil. Among the biological factors that influence the formation and stabilization of soil aggregates, arbuscular mycorrhizal fungi (AMF) are distinguished due to extrarradicular hyphae and glomalin production. In this context, the objective of this study was to evaluate different AMF (Acaulospora colombiana, Acaulospora longula, Acaulospora morrowiae, Paraglomus occultum and Gigaspora margarita) associated with Urochloa brizantha (A. Rich.) Stapf on soil aggregate stability. The study was conducted in a completely randomized design, using an Oxisol and autoclaved sand 2:1 (v/v), with seven treatments: five AMF; and treatments with plants without inoculation and with only the soil, with 5 replicates. The experiment was conducted during 180 days and the following variables were evaluated: mycelium total length (TML); production of easily extractable glomalin-related soil protein (GRSP) in the soil and aggregate classes; stability of the dry and immersed in water aggregates through the mean geometric diameter (MGD) and the mean weighted diameter (MWD) of aggregates; and the soil aggregate stability index (ASI). It was observed that the inoculation favored soil aggregation, with a high incidence of A. colombiana, which presented the highest MGD, TML and GRSP production in the aggregates with Ø>2.0mm and for A. colombiana and A. morrowiae in the aggregates with Ø<0.105 mm, when compared to the treatment without inoculation. These results show that there is a distinction between the effects of different AMF on the formation and stability of soil aggregates.
This study evaluated the effect of inoculation with a mixture of spores of arbuscular mycorrhizal fungi (AMF) (Glomus macrocarpum, Paraglomus occultum, and Glomus sp.) on the initial establishment of Acacia mangium, Sorghum bicolor, and Urochloa brizantha in soil contaminated with heavy metals. The experiment was conducted in a greenhouse, in plastic pots containing 1.8 kg of soil, which presented 7200, 1140, 480, and 72 mg of Zn, Cu, Pb, and Cd, respectively. The chlorophyll content (SPAD index) of inoculated plants of A. mangium and U. brizantha was higher than those of non-inoculated plants (p < 0.05). No differences were detected for the concentration of heavy metals in plant shoots, whether the plant was inoculated or not. However, inoculated plants had greater root length (S. bicolor and U. brizantha) (p < 0.05) and greater plant height (A. mangium) (p < 0.05). The present results demonstrate that the beneficial effects of AMF on plant growth and the alleviation of contaminants are imperative factors for the rehabilitation of soils contaminated with heavy metals.
Arbuscular mycorrhizal fungi (AMF) may exhibit distinct behaviors when associated with the same species of host plant, being necessary to understand their ecology, in order to optimize their management and maintenance in germplasm bank. This study aimed to evaluate different AMF associated with Urochloa brizantha (A. Rich.) Stapf by analyzing the symbiosis establishment time, spore multiplication and production of glomalin-related soil protein. The experiment was carried out in a completely randomized design, in a 6 x 5 arrangement (five AMF species, non-inoculated control treatment and five evaluation times). The following aspects were analyzed: plant growth, spore multiplication, mycorrhizal colonization and glomalin production. The highest number of spores occurred for Acaulospora longula and A. colombiana, exhibiting the highest mycorrhizal colonization at 76 days. The inoculation favored the root growth of U. brizantha at 15 days of cultivation, plant height and root dry matter at 60 days and shoot dry matter at 90 days, especially for the Acaulospora species. The inoculation with A. colombiana, A. longula and Paraglomus occultum resulted in increased glomalin at 120 days. Gigaspora margarita and P. occultum did not reach the maximum colonization and spore multiplication, indicating that a period of time longer than 120 days of cultivation is necessary.
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