SILICATE MINERAL ALTERATION IN THE RHIZOSPHERE OF NORWAY SPRUCE IN THREE CATCHMENTS OF THE SLAVKOV FOREST, CZECH REPUBLIC

Silicate minerals are key components in supplying non-nitrogen nutrients in soils. Many laboratory studies have shown that microbes and symbiotic fungi play a vital role in nutrient acquisition of plants. Mycorrhizal fungi, bacteria, and biofilm in the rhizosphere enhance chemical weathering and provide nutrients for their hosts under limiting conditions. However, the contribution of biological weathering of silicate minerals in natural forest soils remains controversial.

In this study, mesh bags containing 3 wt% of a silicate mineral, and quartz sand, were buried in spruce forest soils for five years. Three catchments were selected in the Slavkov Forest, Czech Republic, with different bedrock geology, serpentinite (K limited), leucogranite (Mg limited) and amphibolite (no limitations). The mesh bags were buried in three sites per catchment. The mesh size was 60 µm, which allowed fungal hyphae and bacteria to colonize the bags, but excluded direct plant-root contact with the minerals. This design allowed us to test the direct contribution of fungi and bacteria to weathering of six silicate minerals under naturally occurring K and Mg limitations.

Mineral grain surfaces were analyzed using scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDXS) and atomic force microscopy (AFM).

The preliminary microscopy study documented dissolution features such as etch pits, channels, and rounded edges of the minerals. AFM provided nanoscale morphology of a thin biolayer, bacterial, and fungal hyphal attachment on biotite and muscovite surfaces from all sites. SEM showed that all six minerals were extensively weathered from each catchment. EDXS was not able to provide information about chemical alterations of the surfaces. Macroscopically, mesh bags from the serpentinite and amphibolite sites have higher fungal biomass than those from the leucogranite site.

The extensive surface alterations of all grains cannot be explained by the observed fungal hyphal attachments and biological materials in the bags. Abiotic dissolution processes might dominate the alteration patterns after 5 years of incubation in the soils. In further studies, quantification of the amount of organic matter, microbial and fungal community, and alteration of the mineral surfaces at each site will be completed.