The Relationship Between Soil Air Filled Porosity and Soil Methane Oxidation is Almost Identical in Both Dry and Wet Temperate Eucalypt Forests

Abstract:

In order to gain a better understanding of the temporal variation in soil methane (CH₄) exchange in temperate evergreen eucalypt forests in south-eastern Australia we measured soil CH₄ exchange in high temporal resolution (every 2 hours or less) over two consecutive years (Wombat State Forest, Victoria, AUS) and over one year (Warra, Tasmania, AUS) in two temperate Eucalyptus obliqua (L. Her) forests with contrasting annual precipitation (Wombat State Forest = 870 mm yr^-1, Warra = 1700 mm yr^-1). Both forests were continuous CH₄ sinks with the Victorian site having a sink strength of -1.79 kg CH₄ ha^-1 yr^-1 and the Tasmanian site having a sink strength of -3.83 kg CH₄ ha^-1 yr^-1. Our results show that CH₄ uptake was strongly controlled by soil moisture at both sites and explained up to 90% of the temporal variability in CH₄ uptake. Furthermore, when soil moisture was expressed as soil air filled porosity (AFP) we were able to predict the CH₄ uptake of one site by the linear regression between AFP and CH₄ uptake from the other site. Soil temperature only had an apparent control over seasonal variation in CH₄ uptake during periods when soil moisture and soil temperature were closely correlated. The fluctuation of the generally low soil nitrogen levels did not influence soil CH₄ uptake at either site.