Soil macrofauna and nitrogen on a sub-Antarctic island

Area of Science:

• Ecology
• Soil Science
• Sub-Antarctic Ecology

Background:

• Sub-Antarctic islands like Marion Island exhibit high primary production, necessitating substantial nutrient uptake by vegetation.
• Nutrient requirements are primarily met through the mineralization of organic matter reserves.
• Microbial nitrogen mineralization alone is insufficient to support observed vegetation nitrogen uptake rates.

Purpose of the Study:

• To describe the densities, diets, and habitat preferences of soil macrofauna on Marion Island.
• To assess the role of soil macrofauna in nitrogen (N) cycling within a mire-grassland ecosystem.
• To determine the contribution of soil fauna to peat N mineralization.

Main Methods:

• Field surveys to determine soil macrofaunal densities, diets, and habitat preferences.
• Microcosm experiments to quantify inorganic nitrogen release mediated by soil fauna and microorganisms.
• Extrapolation of microcosm data to estimate the contribution of soil macrofauna to island-wide N mineralization.

Main Results:

• Soil macroinvertebrates and bacteria, despite being a small fraction of the total nitrogen pool, are responsible for most peat N mineralization.
• Earthworms and other soil macrofauna significantly stimulate inorganic nitrogen release in microcosms.
• Extrapolated results indicate that soil macrofauna stimulate sufficient N release to meet maximum vegetation N uptake rates during the growing season.

Conclusions:

• The soil faunal component, particularly earthworms, plays a crucial role in driving nutrient cycling on Marion Island.
• Soil macrofauna significantly enhance nitrogen availability, compensating for insufficient microbial mineralization rates.
• The findings likely apply to nutrient cycling dynamics on other sub-Antarctic islands.