World Congress of Soil Science Logo 18th World Congress of Soil Science
July 9-15, 2006 - Philadelphia, Pennsylvania, USA
International Union of Soil Sciences

Monday, 10 July 2006 - Friday, 14 July 2006
141-4

This presentation is part of 141: 2.3B Molecular Approaches to Microbial Ecology in Soils - Poster

Controls on Biological Activity in Soils from Antarctic Dry Valleys.

David W. Hopkins, School of Biological and Environmental Sciences, Univ of Stirling, Stirling, FK94LA, United Kingdom, Ashley D. Sparrow, Dept of Natural Resources and Environmental Sciences, Univ of Nevada, Reno, NV 89512, Edward G. Gregorich, Agriculture & Agri-Food Canada, Central Experimental Farm, Ottawa, ON K1A0C6, Canada, Bo Elberling, Institute of Geography, Univ of Copenhagen, Copenhagen, DK-1350, Denmark, Laurence G. Greenfield, Univ of Canterbury, School of Biological Sciences, Private Bag 4800, Christchurch, New Zealand, and Phil Novis, Manaaki Whenua - Landcare Research, Lincoln, 8152, New Zealand.

The Antarctic dry valleys are characterised by extremely low temperatures, dry conditions and lack of conspicuous terrestrial autotrophs, but the soils contain organic C, emit CO2 and support communities of heterotrophic soil organisms. We have examined the role of modern lacustrine detritus as a driver of soil respiration in the Garwood Valley, Antarctica, by characterizing the composition and mineralization of lacustrine detritus and soil organic matter and relating these to soil respiration and the controls on soil respiration. Laboratory mineralization of organic C in soils from different, geomorphically-defined, landscape elements at 10˚C was comparable with decomposition of lacustrine detritus (mean residence times between 115-345 d for the detritus and 410-1670 d for soil organic matter). The chemical composition of the detritus (C-to-N ratio = 9:1 12:1 and low alkyl-C-to-O-alkyl-C ratio in solid-state 13C nuclear magnetic resonance spectroscopy) indicated that it was a labile, high quality resource for micro-organisms. Initial (0-6 d at 10˚C) respiratory responses to glucose, glycine and NH4Cl addition were positive in all the soils tested, indicating both C and N limitations on soil respiration. However, over the longer term (up to 48 d at 10˚C) differential responses occurred. Glucose addition led to net C mineralization in most of the soils. In the lake shore soils, which contained accumulated lacustrine organic matter, glucose led to substantial priming of the decomposition of the indigenous organic matter, indicating a C or energetic limitation to mineralization in that soil. By contrast, over 48 d, glycine addition led to no net C mineralization in all soils except stream edge and lake shore soils, indicating either substantial assimilation of the added C (and N), or no detectable utilization of the glycine. The Q10 values for basal respiration over the -0.5 to 20˚C temperature range were between 1.4 and 3.3 for the different soils, increasing to between 3.4 and 6.9 for glucose-induced respiration, and showed a temperature dependence. In all except the lake shore soils, the activation energy for glucose-induced respiration was significantly greater than for basal respiration, suggesting that most soils were not well-adapted to large substrate additions. The different response in the lake shore soil indicated that the community in this soil was equally able to mineralize both the indigenous organic C and the added glucose C. Taken together, our results strongly support contemporaneous lacustrine detritus, blown from the lake shore, as an important driver of soil respiration in Antarctic dry valleys.

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