Abiotic Controls of Soil Respiration Beneath an Eighteen-Year-Old Pinus Radiata Stand in South-Eastern Australia

Abstract

(1) The influence of soil moisture and temperature on soil respiration beneath an eighteen-year-old Pinus radiata stand in south-eastern Australia were examined. Soil respiration was measured by a soda-lime absorption technique, measurements being conducted at fourteen-day intervals over a 262-day period. (2) Soil respiration followed a seasonal pattern with a maximum (0.89 g CO2 m-2 h1) value occurring during a period of high moisture and temperature; a minimum (0.23 g CO2 m-2 h-1) was associated with low soil moisture availability (when respiration was independent of temperature). (3) Two models, GRESP and BRESP (which use soil moisture and temperature to predict soil respiration), showed a poor fit with measured soil respiration (r2 = 009 and 0 15, respectively), both models overestimating respiration at low soil moisture levels. This occurred because the Qlo quotient had a fixed value in both models. In an effort to improve the fit between measured and modelled respiration the GRESP model was modified by the inclusion of a moisture dependent Qlo term, producing a new model: FRESP. This gave an excellent fit with measured respiration (r2=0 85) because of its moisture-dependent Qlo term. (4) It is concluded that under conditions of low moisture availability, the Qlo quotient is strongly moisture-dependent. To model soil respiration successfully under dry conditions a moisture-dependent Qlo term is required.