THESIS
2017
xxii, 256 pages : illustrations (some color) ; 30 cm
Abstract
Insufficient ecological restoration of man-made habitats on restored landfill sites is commonly
observed. It would be advantageous to promote better plant growth, focusing on the roles of
symbiotic arbuscular mycorrhizal (AM) fungi and soil amendments (biochar). Restoration, such
as plant, bacterial and fungal establishment, imposes considerable effects on soil physical stability
that is related to safety. The objectives of this research were to 1) investigate the ecological
performance in both the restored South East New Territories (SENT) landfill in Hong Kong, and
the Xiaping (XP) landfill (with biochar) in Shenzhen, China, and 2) study the effects of AM fungi
on the relevant geotechnical properties.
At the two restored landfill sites, plant communities were surveyed. Soil ba...[
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Insufficient ecological restoration of man-made habitats on restored landfill sites is commonly
observed. It would be advantageous to promote better plant growth, focusing on the roles of
symbiotic arbuscular mycorrhizal (AM) fungi and soil amendments (biochar). Restoration, such
as plant, bacterial and fungal establishment, imposes considerable effects on soil physical stability
that is related to safety. The objectives of this research were to 1) investigate the ecological
performance in both the restored South East New Territories (SENT) landfill in Hong Kong, and
the Xiaping (XP) landfill (with biochar) in Shenzhen, China, and 2) study the effects of AM fungi
on the relevant geotechnical properties.
At the two restored landfill sites, plant communities were surveyed. Soil bacterial and AM
fungal communities were quantified using 16S and 18S rRNA genes, respectively. Three grass
species were used as the hosts of AM fungi in three different experiments in the laboratory. The
effects of AM fungi on soil matric suction, soil hydraulic conductivity and root tensile strength
were investigated.
At the SENT landfill, plant diversity was higher, while bacteria and AM fungi was lower,
compared with an adjacent natural site. Less native species (50% less) were observed in the
restored site, which consisted of different plant, soil bacterial and AM fungal communities to the
natural site (P < 0.05, analysis of similarity), 15 years after restoration. For the XP landfill, biochar amendments significantly increased plant diversity, number of species, number of individuals and
evenness. The diversity and number of species for bacteria and AM fungi were also increased.
Mycorrhizal treatments (MT) in the root zone retained a lower soil suction (~10 kPa less) at a
depth of 30 mm, but a higher suction (~5 kPa more) at a depth of 75 mm (root zone), compared
with non-mycorrhizal treatment (NM), during 30 min of wetting. During drying, the soil of MT
tended to dry more slowly than NM. Root biomass was a key factor in retaining suction. Soil
hydraulic conductivity did not significantly correlate with the concentration of AM fungal
glomalin.
Root tensile strength was enhanced (species-dependently) by AM fungi. This enhancement
ranged from 17 to 64% was associated with higher cellulose and hemicellulose content. Soil
cohesion would be increased by enhanced root tensile strength (~45% more) and enhanced root
biomass due to AM fungi, contributing to the resistant force, making the plant-soil system more
stable.
The present research points to limitations of current practice in ecological restoration, and
proposes a method for restoring plant, bacterial and AM fungal communities. The initial selection
of plant species and adjustment of soil properties to be similar to the natural environment are
essential. The interaction between plant and AM fungi can impose considerable effects on the
physical stability of the plant-soil system, especially through enhancing plant biomass and root
tensile strength.
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