Ecosystem Respiration in a Seasonally Snow-Covered Subalpine Grassland

Abstract

Ecosystem respiration is important because it is the small imbalances between CO2 uptake via photosynthesis and CO2 release by ecosystem respiration that determine the effect of the biosphere on atmospheric CO2. For subalpine grasslands with mild winters we do not know the size of under-snow respiration relative to the total annual ecosystem respiration. This study determines the contribution of respiration through snow to total annual respiration, and models annual ecosystem respiration based on relationships with soil temperature and water content. Measurements were made monthly for two years in an unmanaged subalpine grassland in the Snowy Mountains of Australia. The vegetation is sparse (aboveground mass = 355–605 g m−2, belowground mass = 570–1010 g m−2) and dominated by native perennial C3 grasses and sedges. Ecosystem respiration was positively related to temperature, and there was some evidence that ecosystem respiration was more temperature sensitive at temperatures between 0 and 2 °C than at warmer temperatures. Annual ecosystem respiration was 12.1 Mg C ha−1 yr−1 in 2007/2008 and 10.5 Mg C ha−1 yr−1 in 2008/2009. Maximum daily rates of ecosystem respiration of 7 µmol CO2 m−2 s−1 occurred during summer, while minimum rates occurred under snow cover and were 0.2 to 0.9 µmol CO2 m−2 s−1. The duration of permanent snow cover was 60–68 days (equivalent to 16–18% of the year) and ecosystem respiration under snow was 4.1 to 4.3% of annual ecosystem respiration, which is smaller than the 10–50% commonly reported from studies in areas with longer snow-covered periods.