José Oswaldo Siqueira

Mycorrhizal colonization and mycotrophic growth of native woody species as related to successional groups in Southeastern Brazil

Abstract Differences in arbuscular mycorrhizal colonization, mycotrophic growth and response to superphosphate were studied in seedlings of 28 native woody species belonging to different successional groups in woodland fragments in the state of Minas Gerais, Southeastern Brazil. The experiment was carried out in a glasshouse in plastic bags filled with a soil-mix composed of soil+burnt rice shell (6:1 v/v) amended or not with superphosphate (Control, P) and infested or not with a mixture of arbuscular mycorrhizal (AM) fungi Glomus etunicatum Becker and Gerdermann and Gigaspora margarita Becker and Hall (M) and co-application of P and M (MP), with 10 replications per species. Successional groups were represented by 8, 5, 4 and 11 species of pioneers, early secondary, late secondary and climax species, respectively. It was found that dry matter yield of climax species was 6.8-fold higher than the pioneer ones in control treatments. However, pioneers were markedly more responsive to soil-mix treatments than climax ones. Based upon shoot dry matter, overall response for M, P and MP overcontrols was 813, 575 and 1688% for pioneers and 0, 48 and 106% for climax ones. Mycorrhizal effects were much greater in soil-mix with no added P than when superphosphate was added. They were maximum and consistent among pioneers and markedly diminished in climax species in which positive response to M was found in only 27% of the species of this group. AM colonization ranged from 0 to 81% of the root length colonized and it was inversely related to succession and directly related to mycorrhizal response. Growth responses to soil-mix treatments were inversely related to seed weight and to succession. Pioneer species have light seeds, high susceptibility to infection and colonization rate and are responsive to both mycorrhiza and superphosphate, whereas, late successional species are more dependent upon their seed reserves than upon AM and superphosphate for initial growth. However, late successional species may become mycorrhiza-dependent in later growth stages. The Glomalean fungi and soil phosphorus are important factors in light of the forest ecology and reforestation technology in low-fertility soils in the tropics.

Species richness and spore abundance of arbuscular mycorrhizal fungi across distinct land uses in Western Brazilian Amazon

Arbuscular mycorrhizal fungi (AMF) were surveyed for species richness and abundance in sporulation in six distinct land uses in the western Amazon region of Brazil. Areas included mature pristine forest and sites converted to pasture, crops, agroforestry, young and old secondary forest. A total of 61 AMF morphotypes were recovered and 30% of them could not be identified to known species. Fungal communities were dominated by Glomus species but Acaulospora species produced the most abundant sporulation. Acaulospora gedanensis cf., Acaulospora foveata, Acaulospora spinosa, Acaulospora tuberculata, Glomus corymbiforme, Glomus sp15, Scutellospora pellucida, and Archaeospora trappei sporulated in all land use areas. Total spore numbers were highly variable among land uses. Mean species richness in crop, agroforestry, young and old secondary forest sites was twice that in pristine forest and pasture. fungal communities were dominated in all land use areas except young secondary forest by two or three species which accounted for 48% to 63% of all sporulation. Land uses influenced AMF community in (1) frequency of occurrence of sporulating AMF species, (2) mean species diversity, and (3) relative spore abundance. Conversion of pristine forest into distinct land uses does not appear to reduce AMF diversity. Cultural practices adopted in this region maintain a high diversity of arbuscular mycorrhizal fungi.

Atributos biológicos indicadores da qualidade do solo em sistemas de manejo na região do cerrado no sul do estado de Goiás

Latosols (Oxisols) under cerrado vegetation have been intensively incorporated into the agricultural production process. However, studies involving soil quality in this environment are scarce. The objective of this work was to verify alterations on aggregation attribute indicators of soil quality, as a result of the management systems adopted for the native cerrado, and to select the best attributes indicating such alterations. The samples were collected at depths of 0-10, 10-20, and 20-40 cm from a typic Dystrophic Red Latosol (Oxisol) in Morrinhos, Goias State, Brazil. The following attributes were evaluated: mean geometric diameter (MGD), percentage of aggregates > 2 mm, percentage of aggregates 2 mm aggregate class (0.852*), and a negative correlation (-0.903**) with the 2 mm- and < 0.25 mm-aggregate groups were good indicators for alterations in relation to the native cerrado and can be suggested as useful components for the elaboration of a regional soil quality index.

Efeitos do glifosato sobre microrganismos simbiotróficos de soja, em meio de cultura e casa de vegetação

The effects of the Roundup herbicide on three strains of Bradyrhizobium elkanii (BR 29, INPA 80A and INPA 553A), one of B. japonicum (BR 86), and on three species of arbuscular mycorrhizal fungi (AMF) (Gigaspora margarita,Glomus etunicatum and Scutellospora heterogama), were evaluated in culture media containing increasing concentrations of the herbicide (0_454 µM); evaluations were also made on the effects on nodulation and mycorrhiza colonization of soybean grown in a soil treated with Roundup doses equivalent to 1.25 to 10 L ha-1 before sowing. The herbicide inhibited growth of Bradyrhizobium spp. and AMF in culture medium. These effects were directly related to increasing concentrations, and varied depending on the strain and species evaluated. However, in vitro inhibition occurred only when concentrations were greater than that recommended for use in the field. Strains BR 29, INPA 553A and INPA 80A showed to be more resistant to glyphosate, when compared to BR 86. Herbicide inhibition on germination and growth of AMF spore germ tubes decreased from G. etunicatum to S. heterogama and G. margarita. Soil application of Roundup before sowing up to a dose equivalent to 10 L ha-1 had no effect on nodulation and mycorrhiza colonization of soybean.

Synergistic effects of vesicular-arbuscular mycorrhizal fungi and diazotrophic bacteria on nutrition and growth of sweet potato (Ipomoea batatas)

SummarySweet potatoes were micropropagated and then transplanted from axnic conditions to fumigated soil in pots in the greenhouse. Spores of Glomus clarum were obtained from Brachiaria decumbens or from sweet potatoes grown in soil infected with this fungus and with an enrichment culture of Acetobacter diazotrophicus. Three experiments were carried out to measure the beneficial effects of vesicular-arbuscular mycorrhizal (VAM) fungi-diazotroph interactions on growth, nutrition, and infection of sweet potato by A. diazotrophicus and other diazotrophs obtained from sweet potato roots. In two of these experiments the soils had been mixed with 15N-containing organic matter. The greatest effects of mycorrhizal inoculation were observed with co-inoculation of A. diazotrophicus and/or mixed cultures of diazotrophs containing A. diazotrophicus and Klebsiella sp. The tuber production was dependent on mycorrhization, and total N and P accumulation were increased when diazotrophs and G. clarum were applied together with VAM fungal spores. A. diazotrophicus infected aerial plant parts only when inoculated together with VAM fungi or when present within G. clarum spores. More pronounced effects on root colonization and intraradical sporulation of G. clarum were observed when A. diazotrophicus was co-inoculated. In non-fumigated soil, dual inoculation effects, however, were of lower magnitude. 15N analysis of the aerial parts and roots and tubers at the early growth stage (70 days) showed no statistical differences between treatments except for the VAM+Klebsiella sp. treatment. This indicates that the effects of A. diazotrophicus and other diazotrophs on sweet potato growth were caused by enhanced mycorrhization and, consequently, a more efficient assimilation of nutrients from the soil than by N2 fixation. The possible interactions between these effects are discussed.

Mycorrhiza and phosphate protection of tropical grass species against heavy metal toxicity in multi-contaminated soil

In this paper, the effects of arbuscular mycorrhizal (AM) fungi and phosphate amendments on protection of the tropical grass Brachiaria decumbens Stapf. against metal toxicity caused by Zn, Cd, Cu, and Pb were studied in a sterilized soil. Plants inoculated with a mixture of AM fungi (Acaulospora morrowiae, Gigaspora albida, and Glomus clarum) isolated from a heavy-metal-contaminated site or amended with P (added as triple superphosphate) exhibited marked positive growth responses, indicating the ameliorating effects of these two factors. Soil metal concentrations needed to inhibit plant growth by 50% were around twofold higher for AM plants as compared to those for non-inoculated ones. Similarly, phosphate showed ameliorating effects for B. decumbens, but its effects were not related to mycorrhizal conditions. Although mycorrhiza and phosphate act independently, their protecting effects were additive. Metal bioaccumulation factor of B. decumbens is high, especially for Cd; but AM inoculation prevents metal transference from roots to shoots, retaining these metals in the roots. AM fungus and phosphate represent a promising tool for enhancing ground vegetation in heavy-metal-contaminated sites.

Arbuscular mycorrhizal inoculation and superphosphate application influence plant development and yield of coffee in Brazil

Abstract This paper reports a 6-year field study of the effects of mycorrhizal pre-colonization of coffee seedlings on initial crop development and coffee bean yield in a low-fertility Oxisol amended with superphosphate (P) at planting. The experiment included five P rates (0, 20, 40, 80 and 160 g plant–1 P2O5) combined with seven fungal treatments [non-mycorrhizal control, pre-colonization with a mix of Glomus clarum and Gigaspora margarita (CM) and with five isolates of Glomus etunicatum]. Inoculated and non-inoculated outplants were raised under glasshouse conditions, transplanted into the field in January 1989 and monitored until July 1995. Plant height and stem diameter were greatly enhanced by P application and were higher in mycorrhizal seedlings than in controls up to 19 months after transplanting (MAT) but were not different at 26 MAT. Inoculation effects on tree canopy diameter were significant up to 26 MAT, at which time mycorrhizal colonization was high (43–55%), but did not differ amongst plants, regardless of whether or not the plants had been pre-colonized at the nursery stage. Root colonization and spore number in the soil were reduced by high P rates at 26 MAT. The first bean yield (1991) was highly enhanced by P and all pre-colonization treatments (38% increment over control) and these factors showed a significant interaction. Three isolates of G. etunicatum showed yield enhancements above 50%. The P rate for maximal yield was 207 g plant–1 P2O5 for non-pre-colonized and approximately 100 g plant–1 for pre-colonized plants. For this harvest, the mycorrhizal biofertilizer effect was equal to 254 kg ha–1 P2O5. In subsequent years, pre-colonization effects were reduced and inconsistent. In 1992, 1993 and 1995, yield was affected by P but not by mycorrhizal inoculation. In 1994 there was a P versus mycorrhiza interaction and CM and G. etunicatum-Var gave higher yields than non-precolonized plants. Considering accumulated yield for this 5-year period, P application resulted in high yield increment in all treatments, whereas pre-colonization effects were extremely diminished. However, despite inconsistency amongst mycorrhizal treatments, pre-colonization effects were detected at the fifth harvest in some fungal treatments. Based on the total yield of five harvests, maximal productivity was achieved with CM at 20 g plant–1 P2O5 and with CM and G. etunicatum-Var at the highest P rate. Diminishing mycorrhizal effects over time are related to colonization of non-precolonized seedlings by the indigenous fungi and to the reduced external P requirement of the mature crop. If adequate phosphorus is applied at planting, pre-colonization of outplants with selected arbuscular mycorrhizal fungi enhances early crop development and productivity of coffee in low-fertility soils of Brazil.

Occurrence and diversity of arbuscular mycorrhizal fungi in trap cultures from soils under different land use systems in the Amazon, Brazil

The aim of this work was to evaluate the occurrence of arbuscular mycorrhizal fungi (AMF) species diversity in soil samples from the Amazon region under distinct land use systems (Forest, Old Secondary Forest, Young Secondary Forest, Agroforestry systems, Crops and Pasture) using two distinct trap cultures. Traps established using Sorghum sudanense and Vigna unguiculata (at Universidade Regional de Blumenau -FURB) and Brachiaria decumbens and Neonotonia wightii (at Universidade Federal de Lavras - UFLA) were grown for 150 days in greenhouse conditions, when spore density and species identification were evaluated. A great variation on species richness was detected in several samples, regardless of the land use systems from where samples were obtained. A total number of 24 AMF species were recovered using both methods of trap cultures, with FURBs traps yielding higher number of species. Acaulospora delicata, A. foveata, Entrophospora colombiana and two undescribed Glomus species were the most abundant and frequent species recovered from the traps. Number of species decreased in each genus according to this order: Acaulospora, Glomus, Entrophospora, Gigaspora, Archaeospora, Scutellospora and Paraglomus. Spore numbers were higher in Young Secondary Forest and Pastures. Our study demonstrated that AMF have a widespread occurrence in all land use systems in Amazon and they sporulate more abundantly in trap cultures from land uses under interference than in the pristine Forest ecosystem.

Avaliação agronômica de um biossólido industrial para a cultura do milho

The objective of this work was to evaluate the agronomic feasibility of an industrial biosolid for corn. The experiment was carried out on a dystrophic Cambisol in two cropping seasons, 1999/2000 and 2000/2001. The application of 0, 6, 12, 18 and 24 Mg ha-1 of biosolid dry matter basis, supplemented with K2O in both trials and with 1/3 of the recommended P2O5 rate in the second trial was compared to the complete mineral fertilization. Biosolid application enhanced soil fertility, crop nutrition and grain productivity. Yield response to doses was quadratic, and reached the maximum of 9,992 kg ha-1 with 22.5 Mg ha-1 of biosolid, 21% higher than the complete mineral fertilization and 74% higher than the control with no fertilizer added. Even in the largest biosolid dose, no symptom of nutrients, sodium or heavy metals toxicity was found. The equivalence in productivity to the mineral fertilization (7,895 kg ha-1) was attained with 10 Mg ha-1 of biosolid. Based on this equivalence to NPK, the biosolid fertilizer value was estimated in R

Crescimento e teor de metais de mudas de espécies arbóreas cultivadas em solo contaminado com metais pesados

43.70 per Mg for dry residue and in R