Soil Carbon and Nitrogen and Evidence for Formation of Glomalin, a Recalcitrant Pool of Soil Organic Matter, in Developing Mount St. Helens Pyroclastic Substrates

Abstract

Formation of stable soil organic matter is typically the result of a relatively slow series of decomposition processes that can be constrained in early successional sites. Alternatively, compounds such as glomalin, a glycoprotein produced by arbuscular mycorrhizal fungi, may form relatively early during soil development and improve aggregate stabilization, water infiltration, and carbon and nitrogen storage. After 31 years of development, significant amounts of soil C, N, and BRSP, an indicator of glomalin, had accrued in pyroclastic deposits, in patterns affected by both plant community type and soil depth. Mycorrhizal fungi are important, but incompletely understood,  drivers of pedogenic processes during primary succession and may exert disproportionate effects on soil processes and plant development prior to the accumulation of humified soil organic matter.

Glossary terms are shown in bold italic face.

Glossary

Arbuscular mycorrhizal fungi

A plant-fungal relationship, found in over 90% of vascular plants, in which the fungus penetrates the cortical cells of the roots and forms highly branched arbuscules and, in some species, vesicles. These fungi provide nutrients and water to plants as well as assisting in soil structure and disease prevention.

Ectomycorrhizal fungi

A plant-fungal relationship, found in about 2% of plant species, particularly woody plants, in which the fungus, primarily basidiomycetes and some ascomycetes, forms a dense hyphal sheath, known as the mantle, around the root surface. The hyphal network may extend several centimeters into the surrounding soil to aid in water and nutrient uptake, often helping the host plant to survive adverse conditions, in exchange for carbohydrates.

Ericoid mycorrhizal fungi

A plant-fungal relationship between members of the plant family Ericaceae, such as blueberries, cranberries, and Rhododendron, and several lineages of fungi in acidic and nutrient poor soils found in boreal forests, bogs, and heathlands. The fungus establishes loose hyphal networks around the outside of hair roots, from which they penetrate the walls of cortical cells to form intracellular coils that can densely pack individual plant cells. The coils function only for a period of a few weeks before the plant cell and fungal hyphae begin to degrade. The coils are where nutrients are exchanged for carbohydrates, and these fungi also have enzymatic capabilities to break down complex organic molecules and act as saprophytes, living on dead or decaying organic matter.

Mycorrhiza(e)

A symbiotic association between a fungus and the roots of a host plant where the body of the fungi are thread-like hyphae that extend the root system. The mycorrhizal association is generally mutualistic, playing important roles in soil biology, chemistry, and physics, but in particular species or in particular circumstances, mycorrhizae may be variously pathogenic in host plants.

Photosynthate

A chemical product of photosynthesis—carbohydrates that are synthesized from carbon dioxide and a source of hydrogen (usually water), using light as an energy source.