Fungal and bacterial weathering of apatite and wollastonite in forest soils
EMSL Project ID
45998
Abstract
Mineral weathering is an important process in biogeochemical cycling because it releases nutrients from less labile pools (e.g., rocks) to the food chain, affects the porosity of earth materials, and influences soil and water composition. Understanding the weathering of apatite (a focus of this proposal) is important for assessing its use in (U-Th)/He and fission track dating, and nuclear waste disposal. A field experiment was undertaken to determine the degree to which fungi and bacteria are responsible for mineral dissolution, especially of Ca-bearing minerals (apatite and wollastonite). The experiment was performed in the northeastern USA, where acid deposition has leached plant-available calcium from soils for decades. Trees obtain soil nutrients through root uptake as well as through mycorrhizal fungi with which they are symbiotically associated. These fungi extend their hyphae from the tree roots into the soil and exude organic acids that may enhance mineral dissolution. The two most common types of symbiotic fungal-tree associations are ectomycorrhizae, which are associated with spruce (Picea), fir (Abies), and beech (Fagus); and arbuscular mycorrhizae which are commonly associated with angiosperms, such as maples (Acer). To examine the role of fungi and bacteria in weathering of Ca- and/or P-bearing minerals, mesh bags containing apatite (Ca5(PO4)3F) or wollastonite (CaSiO3) were buried ~15 cm deep in mineral soil beneath American beech, sugar maple, and mixed spruce and balsam fir stands at the Hubbard Brook Experimental Forest (White Mountains, New Hampshire, USA). Half of the bags were constructed of 50-micrometer mesh to exclude roots but allow fungal hyphae and bacteria to enter the bags; the remaining bags had 1-micrometer mesh to exclude fungi and roots but allow bacteria to enter. The bags were retrieved ~ 1, 2 and 4 years after burial. The main objective of this project is to understand the role that fungi and bacteria play in mineral weathering in forest soils. To achieve this, surfaces of minerals (from the mesh bags) will be examined using scanning electron microscopy (SEM) to identify weathering features such as etch pits and dissolution channels, and determine how the degree of weathering is related to stand type, mycorrhizal association, presence/absence of bacteria, and time. The results of this research will add to our understanding of nutrient availability in forest soils, mineral-microbe interactions, and mineral weathering rates in a field environment. The PI requests use of equipment (an SEM and carbon coater) that is not present on Eastern Washington University's campus. Except for carbon coating, samples have been preprocessed for SEM analysis.
Project Details
Project type
Exploratory Research
Start Date
2012-08-30
End Date
2013-09-08
Status
Closed
Released Data Link
Team
Principal Investigator