Seasonal patterns of soil CO₂ efflux and soil air CO₂ concentration in a Scots pine forest: comparison of two chamber techniques

Abstract

A non‐vented non‐steady state flow‐through chamber and a non‐vented non‐steady state non‐flow‐through chamber technique were used to measure CO2 efflux of a young Scots pine forest on a fertile till soil in southern Finland. Soil temperature, soil moisture and soil CO2 concentration were measured concurrently with CO2 efflux for two and a half successive years. The CO2 efflux showed a seasonal pattern, effluxes ranging from low 0.0–0.1 g CO2 m−2 h−1 in winter to peak values of 2.3 g CO2 m−2 h−1 occurring in late June and in July. The daily average effluxes in July measured by flow through chambers were 1.23 and 0.98 g CO2 m−2 h−1 in 1998 and 1999, respectively. The annual accumulated CO2 efflux was 3117 and 3326 g CO2 m−2 in 1998 and 1999, respectively. The spatial variation in CO2 efflux was high (CV 0.18–0.45) and increased with increasing efflux. Soil air CO2 concentration showed similar seasonal pattern the peak concentrations occurring in July–August. The CO2 concentrations ranged from 580 to 780 µmol mol−1 in the humus layer to 13 620–14 470 µmol mol−1 in the C‐horizon. In winter the soil air CO2 concentrations were lower, especially in deeper soil layers. Drought decreased CO2 efflux and soil air CO2 concentration. The in situ comparison on forest soil between the chamber methods showed the non‐flow‐through chamber to give ∼∼50% lower efflux values than that of the flow‐through chamber. When calibrated against known CO2 efflux ranging from 0.4 to 0.8 g CO2 m−2 h−1 generated with a diffusion box method developed by Widén and Lindroth [Acta Universitatis Agriculturae Suecia Silvestria, 2001], the flow‐through chamber gave equal effluxes at the lower end of the calibration range, but overestimated high effluxes by 20%. Non‐flow‐through chamber underestimated the CO2 efflux by 30%.

Seasonality in a boreal forest ecosystem affects the use of soil temperature and moisture as predictors of soil CO<sub>2</sub> efflux

“…Högberg et al, 2001;Pumpanen et al, 2003a). Our annual estimates, ranging from 1750 to 2050 g CO 2 m −2 for 1998 and 1999, also corresponded to those obtained for some forest ecosystems in the boreal zone (e.g.…”

“…The range of soil CO 2 efflux, 0.044-0.134 g CO 2 m −2 h −1 measured in winter in this study in a pine forest was smaller than that measured in a Finnish spruce stand (Domisch et al, 2006) but similar to the range of efflux in other boreal forests (Winston et al, 1997;Kurganova et al, 2003;Pumpanen et al, 2003a). Our estimates of soil CO 2 efflux for the 6-month winter period were 240 g CO 2 m −2 for the winter of 1998-1999 and 510 g CO 2 m −2 for the following winter.…”

CO<sub>2</sub> flux determination by closed-chamber methods can be seriously biased by inappropriate application of linear regression

“…Jensen et al, 1996;Xu and Qi, 2001;Pumpanen et al, 2003Pumpanen et al, , 2004Reth et al, 2005;Wang et al, 2006). Also, it is often applied to quantify the net CO 2 exchange between the atmosphere and low-stature canopies typical for tundra (Vourlites et al, 1993;Christensen et al, 1998;Oechel et al, , 1998Oechel et al, , 2000Zamolodchikov and Karelin, 2001), peatlands (Alm et al, , 2007Tuittila et al, 1999;Bubier et al, 2002;Nykänen et al, 2003;Burrows et al, 2004;Drösler, 2005;Laine et al, 2006), forest understorey vegetation (Goulden and Crill, 1997;Heijmans et al, 2004) and agricultural crop stands (Dugas et al, 1997;Wagner et al, 1997;Maljanen et al, 2001;Steduto et al, 2002).…”

Exchange of volatile organic compounds in the boreal forest floor

“…The flux calculation in the non-steady-state method is based only on the gas concentration change inside the chamber during the closure, whereas in the steady-state method the removal or adding effect of the through-flow must also be taken into account. The choice of an optimal chamber method (steady-state vs. non-steady-state) has been studied mainly with soil respiration measurements, wherein chamber and collar designs also influence the fluxes measured (Pumpanen et al 2003(Pumpanen et al , 2004. Employment of the steady-state method to measure soil trace gas fluxes produces reliable results (Pumpanen et al 2004, Pape et al 2009, Kolari et al 2012.…”

“…CO 2 emission), being basically temperaturedependent only and peaking in midsummer, showed practically no correlation with VOC fluxes (Pearson's correlation -0.4-0.6) (Figure 8). Methane (CH 4 ) and nitrous oxide (N 2 O) fluxes, measured at the SMEAR II stand, also showed different exchange patterns (Pumpanen et al 2003, Pihlatie et al 2007. The soil at SMEAR II constituted a small sink of CH 4 and oxidation occurred when the soil was well aerated.…”