Measurement of net ecosystem exchange, productivity and respiration in three spruce forests in Sweden shows unexpectedly large soil carbon losses

Abstract

Measurement of net ecosystem exchange was made using the eddy covariance method above three forests along a north-south climatic gradient in Sweden: Flakaliden in the north, Knottåsen in central and Asa in south Sweden. Data were obtained for 2 years at Flakaliden and Knottåsen and for one year at Asa. The net fluxes (N ep ) were separated into their main components, total ecosystem respiration (R t ) and gross primary productivity (P g ). The maximum half-hourly net uptake during the heart of the growing season was highest in the southernmost site with À0.787 mg CO 2 m À2 s À1 followed by Knottåsen with À0.631 mg CO 2 m À2 s À1 and Flakaliden with À0.429 mg CO 2 m À2 s À1 . The maximum respiration rates during the summer were highest in Knottåsen with 0.245 mg CO 2 m À2 s À1 while it was similar at the two other sites with 0.183 mg CO 2 m À2 s À1 . The annual N ep ranged between uptake of À304 g C m À2 year À1 (Asa) and emission of 84 g C m À2 year À1 (Knottåsen). The annual R t and P g ranged between 793 to 1253 g C m À2 year À1 and À875 to À1317 g C m À2 year À1 , respectively. Biomass increment measurements in the footprint area of the towers in combination with the measured net ecosystem productivity were used to estimate the changes in soil carbon and it was found that the soils were losing on average 96-125 g C m À2 year À1 . The most plausible explanation for these losses was that the studied years were much warmer than normal causing larger respiratory losses. The comparison of net primary productivity and P g showed that ca 60% of P g was utilized for autotrophic respiration.

Simulating ectomycorrhiza in boreal forests: implementing ectomycorrhizal fungi model MYCOFON in CoupModel (v5)

“…5). Simulated GPP in this study is generally higher than that by Svensson et al (2008a) but comparable with the measured data from Lindroth et al (2008). It should be noted that the GPP at the southern site, Åsa, was only measured for 1 year and thus can show large uncertainties due to annual variations.…”

“…Figure 5 shows the modeled major ecosystem C fluxes and comparison with previous results by Svensson et al (2008a) and measured data from three other Swedish sites (Flakaliden, Knottåsen, and Åsa ; Fig. 2) at comparable latitudes and on comparable soils by Lindroth et al (2008). The simulated plant gross primary production (GPP) using three approaches all show an increasing trend from the northern sites to the southern sites due to a more favorable climates and N availability for spruce forest growth.…”

“…The sink strength is determined through the balance between major C uptake and release processes, i.e., plant photosynthesis and both autotrophic and heterotrophic respiration, and is largely controlled by nitrogen (N) availability (Magnani et al, 2007;Högberg et al, 2017). Numerous studies have shown that soil N availability is the main driver for plant and microbial dynamics (Vitousek and Howarth, 1991;Klemedtsson et al, 2005;Lindroth et al, 2008;Luo et al, 2012;Mäkiranta et al, 2007;Martikainen et al, 1995). Thus, a proper description of N dynamics in ecosystem models is prerequisite for precisely simulating plant-soil C dynamics and greenhouse gas balance (Maljanen et al, 2010;Schulze et al, 2009;Huang et al, 2011).…”

Development and evaluation of an ozone deposition scheme for coupling to a terrestrial biosphere model

“…Meta-analyses suggest on average a 11 % (Wittig et al, 2007) and a 21 % (Lombardozzi et al, 2013) reduction in instantaneous photosynthetic rates. However, because of carry-over effects, this does not necessarily translate directly into reductions in annual GPP.…”

“…The reduction in net photosynthesis results in reduced growth and hence a reduced leaf area and plant biomass (Morgan et al, 2003;Lombardozzi et al, 2013;Wittig et al, 2009). The tight coupling between photosynthesis and stomatal conductance further affects canopy conductance, and thereby transpiration rates (Morgan et al, 2003;Wittig et al, 2009;Lombardozzi et al, 2013), likely affecting the ecosystem water balance.…”