ABSTRACT
We assessed, in a field experiment, the effects of arbuscular mycorrhizal fungi (Rhizophagus intraradices) and plant growth-promoting bacteria (Azospirillum brasilense) on the soil biological activity and the growth of key pioneer species used in the revegetation of coal-mining areas undergoing recovery. We applied four inoculation treatments to the pioneer plant species (Lablab purpureus, Paspalum notatum, Crotalaria juncea, Neonotonia wightii, Stylosanthes guianensis, Andropogon gayanus and Trifolium repens) used in the recovery process: NI (Control - Non-inoculated), AZO (A. brasilense), AMF (R. intraradices), and co-inoculation of AZO and AMF. On the 75th and 180th days, we measured plant dry mass, mycorrhizal colonization, N and P concentration, and accumulation in plant tissue. We collected soil to quantify glomalin content and soil enzyme activity. After 180 days, we did a phytosociological characterization of the remaining spontaneous plants.The both microorganisms, singly or co-inoculated, promoted increases in different fractions of soil glomalin, acid phosphatase activity, and fluorescein diacetate activity at 75 and 180 days. The inoculation was linked to higher plant biomass production (62-89%) and increased plant P and N accumulation by 34-75% and 70-85% at 180 days, compared with the non-inoculated treatment. Among the pioneer species sown Crotalaria juncea produced the highest biomass at the 75th and 180th days (67% and 76% of all biomass), followed by Lablab purpureus (3% and 0.5%), while the other species failed to establish. At 180 days, we observed twenty spontaneous plant species growing in the area, primarily from the Poaceae family (74%). That suggests that the pioneer species present in the area do not hinder the ecological succession process. Inoculation of R. intraradices and A. brasilense, isolated or combined, increases soil biological activity, growth, and nutrient accumulation in key pioneer plant species, indicating the potential of that technique for the recovery of lands degraded by coal mining.
ABSTRACT
This work aims to characterize the arbuscular mycorrhizal association between maize genotypes and the effects of soil physical-chemical attributes on the symbiosis. A preliminary greenhouse assay evaluated five maize landraces and five conventional modern genotypes in non-sterile, low-P soil. Sixty days after sowing, we measured plant height, stem diameter, shoot and root dry biomass, root colonization structures, and shoot P concentration and total accumulation. In a second stage, a 2-year on-farm study evaluated how soil physical-chemical attributes in fields with three plant genotype groups affected the arbuscular mycorrhizal fungal symbiosis in a maize diversity microcenter in Southern Brazil. We collected soil and plant material in farms growing landrace, conventional modern genotypes, or genetically modified (GM) maize. There were five collection points at each group, and we measured mycorrhizal colonization, soil physicochemical attributes, and shoot phosphorus concentration. The greenhouse study showed that genotypes have different growth strategies for root production and shoot growth. No differences in mycorrhizal colonization rates occurred among landraces and modern maize genotypes in the low-P soil. The field study showed that soil and climate conditions had a more marked effect on mycorrhizal root colonization than plant genotype groups (landrace, conventional modern genotypes, or GM maize).
Subject(s)
Genotype , Mycorrhizae , Plant Roots , Zea mays , Agriculture , Brazil , Mycorrhizae/physiology , Plant Roots/microbiology , Soil/chemistry , Weather , Zea mays/genetics , Zea mays/microbiologyABSTRACT
ABSTRACT: Onion is an important vegetable crop, predominantly grown under conventional tillage system management. Alternatively, the vegetable no-tillage system uses cover crops to form a residue layer, which improves soil physical, chemical, and biological attributes. Aiming to understand the interaction of mycorrhizal and non-mycorrhizal cover crops, phosphatase activity, and soil phosphorus availability and uptake by plants, a no-tillage vegetable production system experiment with onion was carried out in Ituporanga, Southern Brazil. The treatments were black oats (Avena strigosa); rye (Secale cereale); oilseed radish (Raphanus sativus); rye + oilseed radish; black oats + oilseed radish, and a control with spontaneous plants. Additionally, two plots, a conventional tillage system area and a forest, both adjacent to the experiment, were evaluated. We measured cover crop biomass, onion yield, acid phosphatase activity, and resin-extracted phosphorus in the soil, shoot and root phosphorus content, and root colonization in cover crops, spontaneous plants, and onions. The treatments with cover crops had the highest plant biomass in winter and onion yield. Available soil phosphorus and acid phosphatase activity were higher in no-tillage plots than in the conventional tillage system area. The presence of non-mycorrhizal oilseed radish was associated with decreased colonization of rye and onion roots by arbuscular mycorrhizal fungi. No-tillage areas with cover crops or spontaneous plants in winter accumulated more phosphorus than conventional tillage system areas. The conventional tillage system showed adverse effects on most soil attributes, as shown by a Principal Component Analysis.
RESUMO: A cebola é uma importante cultura vegetal, cultivada predominantemente sob sistema de preparo convencional. Como alternativa, o sistema de plantio direto de hortaliças utiliza culturas de cobertura para formar uma camada de biomassa, o que melhora os atributos físicos, químicos e biológicos do solo. Com o objetivo de entender a interação de culturas de cobertura micorrízicas e não-micorrízicas, atividade da fosfatase ácida e disponibilidade e absorção de fósforo do solo pelas plantas, foi realizado um experimento em sistema de plantio direto de hortaliças com a cultura da cebola em Ituporanga, sul do Brasil. Os tratamentos foram: aveia preta (Avena strigosa); centeio (Secale cereale); nabo forrageiro (Raphanus sativus); centeio + nabo forrageiro; aveia preta + nabo forrageiro e um controle com vegetação espontânea. Além disso, duas outras parcelas, uma área em sistema de preparo convencional e uma floresta, ambas adjacentes ao experimento, foram avaliadas. Medimos a biomassa da cultura de cobertura, o rendimento de cebola, a atividade de fosfatase ácida e o fósforo extraído por resina no solo, bem como o conteúdo de fósforo da parte aérea e da raiz e a colonização das raízes em plantas de cobertura, plantas espontâneas e cebolas. Os tratamentos com plantas de cobertura apresentaram a maior biomassa de culturas de cobertura e rendimento de cebola. A atividade de fosfatase ácida e fósforo disponível no solo foram maiores nas parcelas de plantio direto do que na área convencional. A presença de nabo forrageiro, uma planta não micorrízica, foi associada a reduções na colonização de raízes de centeio e cebola por fungos micorrízicos arbusculares. As áreas de plantio direto com plantas de cobertura ou plantas espontâneas no inverno acumularam mais fósforo do que as áreas com preparo convencional. O sistema convencional de lavoura mostrou efeitos adversos para a maioria dos atributos do solo, como mostra a Análise de Componentes Principais.
