CO₂ Fluctuations and CO₂ Fluxes in a Fruit Tree Orchard

Abstract

In the summer, photosynthesis of 11 kg CO₂ ha⁻¹ h⁻¹ of apple trees in an orchard compensated for most of the 12 kg CO₂ lost by respiration of the soil in the tree rows during the day, giving a CO₂ loss of 1 kg CO₂ ha⁻¹ h⁻¹. In the dark, respiration of the soil and trees per hectare of respectively 4 kg ha⁻¹ h⁻¹ and 4.4 kg CO₂ ha⁻¹ h⁻¹ produced 8.4 kg CO₂ ha⁻¹ h⁻¹, identifying the largest CO₂ loss in summer nights, the time when diurnal CO₂ fluctuations in the orchard reached their peak of 630 ppm CO₂. In spring or autumn, soil respiration of 5 kg CO₂ ha⁻¹ h⁻¹ exceeded tree photosynthesis of 3 kg ha⁻¹ h⁻¹ by a factor of two, resulting in a carbon source of 2 kg CO₂ ha⁻¹ h⁻¹ in the light. In the dark, soil and tree dark respiration of 2 and 1.2 kg, respectively, produced a CO₂ source of 3.2 kg CO₂ ha⁻¹ h⁻¹. After leaf fall in the winter, trunks and soil respired 0.12 kg CO₂ and 0.05 kg CO₂, respectively, which classified the orchard as a neglible carbon source of 0.17 kg CO₂ ha⁻¹ h⁻¹ during the winter months.