Soil
Phosphate solubilizing microorganisms and cellulolitic population as biological
indicators of iron mined land rehabilitation
Matias S.R, Passos,
R. Stehmann, J.R. , Lemos-Filho, J.P., Sá N.H, Scotti, M.R.M.
Departamento de Botânica/Instituto de Ciências
Biológicas /Universidade Federal de Minas Gerais
The mining activity is one of the
most important segments of the Brazilian economy. An
area of rupestrian fields, which was used as deposit of mined iron and where no
vegetation was found for 3 years, presented a low soil cellulolytic and
phosphate solubilising microorganisms population. Rehabilitation success of
that site was achieved using two native species, Centrosema coriaceum (Leguminosae) and Tibouchina
multiflora (Melastomataceae),
inoculated with mycorrhizal fungi and/or rhizobia. Efficient strains of Bradyrhizobium sp. were isolated from Centrosema
coriaceum nodules and
were used to inoculate seedlings of Centrosema grown in iron mined soil. Four months old seedlings were transplanted to
the field where C. coriaceum was intercropped with T. multiflora using 3 completely randomized blocks with 2 plots/block corresponding
to the 2 treatments of inoculated
and uninoculated plants. After 24 months, the plant growth, mycorrhizal
colonization, soil cellulolytic and phosphate solubilizing microorganisms (PSM)
were evaluated. It was observed that the growth was significantly improved by
the inoculation procedures. Inoculated plants had higher root colonization and
soil PSM and the cellulolytic population increased in relation to the
uninoculated plots or in relation to the uncultivated area. The results suggest
that the use of efficient strains of Bradyrhizobium and mycorrhizal fungi associated
with native species may be a useful technology for revegetating mined
soil. The PSM and cellulolytic
population may be used as rehabilitation indicators of iron mined land.
Supported by Vale Rio Doce Company
Minas Gerais state has
the Brazilian’s largest iron ore land. Rehabilitation success has been
achieved by the use of native species using beneficial microorganisms such as
rhizobia and mycorrhizal fungi and
the selection of appropriate biological indicators of rehabilitation.
The purpose of the present study was to evaluate the benefit of rhizobia and/or
mycorrhizal fungi for the field establishment of Centrosema coriaceum (Leguminosae) and Tibouchina
multiflora (Melastomataceae) and to evaluate the role
of soil phosphate solubilizing (PS) and cellulolytic microorganisms as
environmental indicator .
The study site is located in the town
of Itabira – MG, Southeast of Brazil, in a mine called Brucutu belonging
to the Vale of Rio Doce Company. The natural vegetation is a rupestrian
fields as showed by Fig 1.
The experimental area
was used as deposit of mined iron and no vegetation was found after being
disabled for 3 years (Fig 2). The floristic studies in
preserved area near to study site allow us to select 2 species with potential
for rehabilitation program : Centrosema coriaceum (Leguminosae) and Tibouchina
multiflora (Melastomataceae).
Rhizobial strains were
previously isolated from nodules of Centrosema coriaceum, collected at preserved area.
Mycorrhizal fungi used were Gigaspora margarita, Scutelospora heterogama and Glomus
etunicatum, from our laboratory collection. Seedlings of Centrosema coriaceum and Tibouchina
multiflora (Melastomataceae) were planted in pots using two treatments: I) Complete
Fertilization (Somasegaran & Hoben, 1985) and II) - Fertilization without
nitrogen plus inoculation with rhizobia strain BHICB- Cc-38 + mycorrhizal fungi
for C. coriaceum and single inoculation of mycorrhizal fungi for T. multiflora. After 120 days, plants
were transplanted to the field (Fig 3) using an experimental design of 3 completely randomized blocks. In each block we have
two plots (2 treatments) with 8 plants /species or 16 plants per plot. Plant
growth and root colonization were evaluated.
Soil samples (0-10 cm deep) were
collected from plots of each
treatment, in preserved site and in impacted site without vegetation. Soil
samples were analysed in relation to the number of Phosphate-Solubilizing
Microorganisms (PSM-Fig 4) as well as cellulolytic, bacteria and fungal population in specific medium. The data
were compared by Tukey’s multiple-range test.
Enhanced C. coriaceum growth was achieved in the inoculated plots, compared to control plots (Figs 5 e 6) and it may be attributed not only to inoculation of Bradyrhizobium sp (BHICB- Cc-38) but also to mycorrhizal colonization as showed in Figure7.
The soil Phosphate-Solubilizing
Microorganims and cellulolytic population were inhibited by soil disturbance
while the total bacteria and
fungal population were not modified. Two years after cultivation an increase in
PSM and cellulolytic microorganisms was observed, specially in soil of
inoculated plots (Fig 8), approaching to the number of the
preserved area.
Conclusions:
The success of the rehabilitation may be determined both quantitatively by plant growth or vegetative cover and qualitatively by soil microorganisms population. Threrefore, we can consider soil PSM and cellulolytic microorganisms as a qualitative rehabilitation indicators.