| In order to re-colonise and stabilise slopes affected by superficial soil failure with plants
essential requirements have to be met:
the plants must grow
the plants must survive sustainably
plant succession must start and continuously develop
These requirements, however, are anything but easy given, particularly under the often hostile
environmental conditions dominating on bare and steep slopes.
Mycorrhizal fungi, the symbiotic partners of almost all plants used in eco-engineering,
are said to improve the plants’ ability to overcome periods governed by strongly (growth)
limiting factors.
Subsequently, results of investigations are presented of mycorrhizal effects on different
plant and soil functions related to eco-engineering in general and soil and slope stabilisation
in particular.
Generally, inoculation yielded higher biomass of the host plants above as well as below
ground. Furthermore, the survival rate was higher for mycorrhized compared to
non-mycorrhized plants, particularly under extreme environmental conditions. However, the
scale of the mycorrhizal impact may be species specific of both the plant host as
well as the fungal partner(s) and often becomes evident only after a certain time
lag.
Depending on the plant-fungus combination the root length per soil volume was found
to be between 0 and 2.5 times higher for inoculated compared to non-inoculated
specimens. On an alpine graded ski slope the survival of inoculated compared to
non-treated Salix herbacea cuttings was significant after one vegetation period only for
one of the three added mycorrhizal fungus species. However, after three years all
of the inoculated plantlets performed significantly better than the non-inoculated
controls.
The analysis of the potential for producing and stabilising soil aggregates of five different
ectomycorrhizal fungi showed high variation and, for the species Inocybe lacera, no
significant difference compared to untreated soil. Furthermore, inoculation of Salix
appendiculata with ecto, arbuscular, and the combination of the two mycorrhizal types
revealed different effects in respect of aggregate stabilisation as well as above and below
ground biomass production of the host plant. Only the ecto-mycorrhized plants significantly
increased soil aggregate stability compared to non-inoculated willows. Significantly higher
production of host plant biomass was restricted to roots and the inoculation with arbuscular
mycorrhiza.
Additionally, there are successional processes in mycorrhizal communities in the way that
perennial plants do have other fungal partners in their juvenile, prime, and senescent
living phase, respectively. It was found that, particularly, in the initial phase of
the re-colonisation and development of a protective vegetation cover, the lack of
relevant (ecto-) mycorrhizal fungi considerably decelerate or even stop succession
processes.
Conclusively, with regard to support and accelerate plant growth and the re-colonisation
and stabilisation of slopes within the scope of eco-engineering measures it is necessary to
select the fungal species based on sound information. This may include ecology and
sociology as well as the potential for aggregate formation depending on the plant species
used. |