Abstract:

The CO₂ efflux of branches and leaves plays an important role in ecosystem carbon balance. Using a carbon flux system, the efflux of Larix gmelinii var. principis-rupprechtii (Dahurian larch) was investigated in 27 years (immature), 31 years (near-mature), and 47 years (mature) stands at diurnal, seasonal, and spatial scales (direction and height) as well as its connection with environmental factors from May to October 2020. Diurnal variation in efflux was a single peak, and the maximum occurring between 14:00 and 16:00. Seasonal variation also exhibited a single peak, with the maximum in late July and the minimum in early October. From May to September, efflux on the south side was the largest among the three stands, and mean values on the south side of 27 year-old, 31 year-old, and 47 year-old trees were 0.50, 0.97 and 1.05 μmol·m^–2·s^–1, respectively. The minimum occurred on the north side. Except for the maximum in July and September in the 27 year-old stand in the middle of the canopy, the maximum efflux in the upper canopy, and the means in the 27 year-old, 31 year-old, and 47 year-old stands were 0.49, 0.96 and 1.04 μmol·m^–2·s^–1, respectively; the minimum occurred in the lower canopy. Temperatures and relative humidity influenced seasonal variations in efflux. Seasonal variation in temperature sensitivity coefficient (Q₁₀) was opposite that of temperature, increasing with decreasing temperature. At the spatial scale, maximum Q₁₀ occurred in the mid canopy. With the efflux and temperature data in different locations, it is possible to better estimate efflux variations in each stand.

Key words: CO₂ efflux, Temperature sensitivity coefficient (Q₁₀), Temporal and spatial variations, Environmental factors