『Abstract
Ectomycorrhiza-forming fungi (EMF) alter the nutrient-acquisition
capabilities of vascular plants, and may play an important role
in mineral weathering and the partitioning of products of weathering
in soils under nutrient-limited conditions. In this study, we
isolated the weathering function of Suillus tomentosus
in liquid-cultures with biotite micas incubated at room temperature.
We hypothesized that the fungus would accelerate weathering by
hyphal attachment to biotite surfaces and transmission of nutrient
cations via direct exchange into the fungal biomass. We combined
a mass-balance approach with scanning electron microscopy (SEM)
and atomic force microscopy (AFM) to estimate weathering rates
and study dissolution features on biotite surfaces. Weathering
of biotite flakes was about 2-3 orders of magnitude faster in
shaken liquid-cultures with fungus compared to shaken controls
without fungus, but with added inorganic acids. Adding fungus
in nonshaken cultures caused a higher dissolution rate than in
inorganic pH controls without fungus, but it was not significantly
faster than organic pH controls without fungus. The K+,
Mg2+ and Fe2+ from biotite were preferentially
partitioned into fungal biomass in the shaken cultures, while
in the nonshaken cultures, K+ and Mg2+ was
lost from biomass and Fe2+ bioaccumulated much less.
Fungal hyphae attached to biotite surfaces, but no significant
surface changes were detected by SEM. When cultures were shaken,
the AFM images of basal planes appeared to be rougher and had
abundant dissolution channels, but such channel development was
minor in nonshaken conditions. Even under shaken conditions the
channels only accounted for only 1/100 of the total dissolution
rate of 2.7×10-10 mol of biotite m-2 s-1.
The results suggest that fungal weathering predominantly occurred
not by attachment and direct transfer of nutrients via hyphae,
but because of the acidification of the bulk liquid by organic
acids, fungal respiration (CO2), and complexation
of cations which accelerated dissolution of biotite. Results further
suggest that both carbohydrate source (abundant here) and a host
with which nutrients are exchanged (missing here) may be required
for EMF to exert an important weathering effect in soils. Unsaturated
conditions and physical dispersal of nutrient-rich minerals in
soils may also confer a benefit for hyphal growth and attachment,
and promote the attachment-mediated weathering which has been
observed elsewhere on soil mineral surfaces.』
1. Introduction
2. Materials and methods
2.1. Mineral and fungus preparation
2.2. Fungal-weathering experiments
2.2.1. Shaken-inorganic
2.2.2. Nonshaken-inorganic
2.2.3. Nonshaken-organic
2.2.4. Edge
2.3. Analyses
2.4. Calculations and statistics
3. Results
3.1. Chemistry
3.1.1. Liquid composition
3.1.2. Fungal biomass composition
3.1.3. Chemical mass-balances
3.2. Scanning electron microscopy
3.3. Atomic force microscopy
4. Discussion
4.1. Fungus-driven surface changes
4.2. Fungal effects on solution chemistry of weathering
4.3. Contribution of edges to fungal weathering
5. Summary and conclusions
Acknowledgments
References