Abstract
Botanical, soil chemistry and soil microbiology variables were tested as predictors of in situ soil respiration rate in the various terrestrial habitats on sub-Antarctic Marion Island (47oS, 38oE). Inorganic P and total N concentration were the best predictors amongst the chemistry variables and bacteria plate count the best of the microbiology variables. However, while these chemistry and microbiology variables could accurately predict soil respiration rate for particular habitats, they proved inadequate predictors across the whole range of habitats. The best suite of predictors comprised only botanical variables (relative covers of five plant guilds) and accounted for 94% of the total across-habitat variation in soil respiration rate. Mean field soil respiration rates (2.1 - 15.5 mmol CO2 m-2 h-1) for habitats not influenced by seabirds or seals are similar to rates in comparable Northern Hemisphere tundra habitats. Seabird and seal manuring enhances soil respiration rates to values (up to 27.6 mmol CO2 m-2 h-1) higher than found at any tundra site. Glucose, N, P or N plus P were added to three habitats with contrasting soil types; a fellfield with mineral, nutrient-poor soil, a mire with organic, nutrient-poor soil and a shore-zone herbfield heavily manured by penguins and with organic, nutrient-rich soil. Glucose addition stimulated soil respiration in the fellfield and mire (especially the former) but not in the coastal herbfield soil. N and P, alone or together, did not stimulate respiration at any of the habitats, but adding glucose to fellfield soils that had previously been fortified with P or NP caused a similar increase in respiration rate, which was greater than the increase when adding glucose to soils fortified only with N. This suggests that fellfield soil respiration is limited by P rather than N, and that there is no synergism between the two nutrients. For the mire and coastal herbfield, adding glucose to soils previously fortified with N, P or NP did not enhance rates more than adding glucose to soils that had received no nutrient pre-treatment.
Highlights
The fauna of sub-Antarctic Marion Island (47 ̊S, 38 ̊E) comprises few grazer or predator species so most energy flow and nutrient cycling occurs in a detritus, rather than a grazing, foodweb
Soil chemistry and soil microbiology variables were tested as predictors of in situ soil respiration rate in the various terrestrial habitats on sub-Antarctic Marion Island (47 ̊S, 38 ̊E)
Soil respiration rate was calculated from the increase in concentration, the system volume and the area of soil enclosed by the chamber
Summary
The fauna of sub-Antarctic Marion Island (47 ̊S, 38 ̊E) comprises few grazer or predator species so most energy flow and nutrient cycling occurs in a detritus, rather than a grazing, foodweb. Whether manuring stimulates soil respiration by improving the inorganic nutrient status of the soil or by supplying it with -respirable carbon sources, or both, was tested by incubating soil samples with added N, P and/or glucose [8]. Glucose markedly stimulated soil respiration rate in all the soils, suggesting that the primary factor limiting soil microbial activity on the island is labile carbon substrate. A goal of the research program at Marion Island is to model carbon exchange for the various terrestrial habitats and for the island as a whole This requires an ability to predict in situ soil respiration rate from the abiotic and biotic factors that affect it. We relate the field-measured soil respiration rates to site factors such as botanical composition, soil chemistry and soil microorganism counts, to see whether any of these factors, or combinations of them, can successfully predict soil respiration rate
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