Plants and mycorrhizal fungi in wind erosion control
In many dry areas around the world, wind
erosion gradually converts fertile land into deserts. Wind tunnel and
laboratory experiments are conducted to investigate how plants and mycorrhizal
fungi protect the soil from wind erosion.
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Sand dunes
immediately beside human settlings on the Tibetan Plateau.
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Wind erosion is the
process by which soil is detached from the ground surface and transported by
wind. All over the world, wind erosion causes huge annual soil losses and
promotes the formation and spreading of deserts, thereby posing a
threat to the livelihood of numerous people. Furthermore, wind erosion increases the content of mineral fine dust
in the atmosphere. High concentrations of fine dust cause lung diseases and
change the global radiation balance, which affects the earth’s climate.
Wind
erosion control
Revegetation
Revegetation of degraded
soils is regarded the most effective strategy against wind erosion. Plants provide both above- and below-ground protection by sheltering the
soil from the erosive force of the wind and stabilising it with their roots,
respectively. However, the conditions on eroded soils are adverse to plant
growth. Hence, revegetation measures are often confronted with major difficulties.
Mycorrhizal
fungi
One way of improving plant
growth on degraded soils is to add mycorrhizal fungi to the soil when seeding
or planting. Almost all plants live in symbiosis with
mycorrhizal fungi, which help them uptake nutrients and water. On degraded soil, there
often exists a lack of mycorrhizal fungi. Therefore, the artificial introduction of mycorrhizal
fungi promises to substantially improve revegetation success. Besides their
beneficial effect on plant growth, mycorrhizal fungi improve soil structure and stability with their vast
underground network of fungal strands (hyphae).
Mycorrhizal fungi provide a twofold benefit in wind erosion
control: On the one hand, they improve
plant growth, and on the other hand, they stabilize the soil (drawings of fungi:
V. Graf).
Investigations
How do plants influence wind erosion processes?
In a 20 m long wind tunnel, we conduct experiments
with grass canopies of different planting densities. In contrast to other wind
tunnel studies, living grasses (Lolium
perenne) are used instead of artificial imitations of vegetation.
At the end of the test section, a sediment
sampler is positioned to trap airborne sand grains at different heights during
the experiment. Furthermore, we measure the fine dust concentration in the air
above the test section. Colored quartz sand is used to visualize erosion and
deposition patterns.
First results show that wind erosion processes
decrease with increasing vegetation cover. A vegetation cover of only 15%
decreased soil loss to 7% and fine dust emission to 50%. A vegetation cover of
55% inhibited these processes almost completely.
Test section (8 m) in
the wind tunnel unplanted and with vegetation covers of 3%, 15% and 55% (from
left to right).
Sediment sampler in
the wind tunnel (left) and accumulations of red quartz sand (right).
Do mycorrhizal fungi improve plant growth on desert-like
soils?
In this study, the adverse soil and climate
conditions of deserts are simulated in a climate chamber. We cultivate various
grass species on sandy, nutrient-poor substrates and water them only rarely. Half
of the grasses are provided with mycorrhizal fungi in the substrate, the other
half not. Thus, it is possible to test whether mycorrhizal fungi improve
survival rate, above-ground biomass production and health of the grasses.
Do mycorrhizal fungi
improve soil resistance to wind erosion?
This study
combines the two previous questions. Erosion processes are investigated in three soil treatments:
a) unplanted soil
b) soil
planted with grasses (without mycorrhizal fungi)
c) soil
planted with grasses and inoculated with mycorrhizal fungi.
In the wind tunnel, all treatments are subjected
to the same wind force. Afterward, we compare the soil losses and fine dust
concentrations. It is assumed that soil erosion rate and fine dust emission is
lowest in the planted and inoculated soil. If experiments confirm this
hypothesis, this will be a strong argument to promote the use of mycorrhizal
fungi in wind erosion control.
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