Seasonal and annual variations in the photosynthetic productivity and carbon balance of a central Siberian pine forest

Abstract

We present a first analysis of data (June 1998 to December 2000) from the long‐term eddy covariance site established in a Pinus sylvestris stand near Zotino in central Siberia as part of the EUROSIBERIAN CARBONFLUX project. As well as examining seasonal patterns in net ecosystem exchange (NE), daily, seasonal and annual estimates of the canopy photosynthesis (or gross primary productivity, GP) were obtained using NE and ecosystem respiration measurements. Although the forest was a small (but significant) source of CO2 throughout the snow season (typically mid‐October to early May) there was a rapid commencement of photosynthetic capacity shortly following the commencement of above‐zero air temperatures in spring: in 1999 the forest went from a quiescent state to significant photosynthetic activity in only a few days. Nevertheless, canopy photosynthetic capacity was observed to continue to increase slowly throughout the summer months for both 1999 and 2000, reaching a maximum capacity in early August. During September there was a marked decline in canopy photosynthesis which was only partially attributable to less favourable environmental conditions. This suggests a reduction in canopy photosynthetic capacity in autumn, perhaps associated with the cold hardening process. For individual time periods the canopy photosynthetic rate was mostly dependent upon incoming photon irradiance. However, reductions in both canopy conductance and overall photosynthetic rate in response to high canopy‐to‐air vapour differences were clearly evident on hot dry days. The relationship between canopy conductance and photosynthesis was examined using Cowan's notion of optimality in which stomata serve to maximise the marginal evaporative cost of plant carbon gain. The associated Lagrangian multiplier (λ) was surprisingly constant throughout the growing season. Somewhat remarkably, however, its value was markedly different between years, being 416 mol mol−1 in 1999 but 815 mol mol−1 in 2000. Overall the forest was a substantial sink for CO2 in both 1999 and 2000: around 13 mol C m−2 a−1. Data from this experiment, when combined with estimates of net primary productivity from biomass sampling suggest that about 20% of this sink was associated with increasing plant biomass and about 80% with an increase in the litter and soil organic carbon pools. This high implied rate of carbon accumulation in the litter soil organic matter pool seems unsustainable in the long term and is hard to explain on the basis of current knowledge.

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

“…The absorbed PAR during the growing season seems to be well related to P g for all sites. The P g values found here are slightly higher than those for the pine forest in Huhus in Finland where the range for the years 1999-2002 was À692 to À1084 g C m À2 year À1 and also much higher compared to the Siberian pine forest which had ca À600 g C m À2 year À1 (Lloyd et al 2002). The Siberian forest has a shorter growing season, which probably explains its lower P g since the daily incoming radiation during the growing season is similar to our sites.…”

“…Thus, the proportion of P g lost as autotrophic respiration is on average 63%. This is comparable to other boreal forests in Canada (Ryan et al 1997) and Siberia (Lloyd et al 2002). The fraction of P g going into total biomass varied between 0.12 and 0.25 (Table 4) with the average being 0.17.…”

“…Both Hyytiälä and Huhus are thin forests of about the same LAI as those studied here. When comparing the half-hourly rates with a Siberian pine forest as well (Lloyd et al 2002) and with a Black spruce and Jack pine forest in Canada (Griffis et al 2003), seasonal pattern and magnitude of maximum net uptake and respiration rates are quite similar. P g = Gross primary productivity, R t = Ecosystem respiration, N ep = Net ecosystem productivity, P TL = Total above ground litter productivity, P RL = Root litter productivity, P B = Biomass productivity, P n = Net primary productivity and D soil = Change in soil carbon content (=À1*N ep À P B ).…”

Precipitation drives interannual variation in summer soil respiration in a Mediterranean-climate, mixed-conifer forest

“…4). Throughout most of the winter, snow covers the ground and both autotrophic and heterotrophic respiration may be limited due to constraints on photosynthesis (e.g., Lloyd et al 2002;Monson et al 2002) and subsequent limitations in labile carbon substrates for decomposers (e.g., Brooks et al 2004, Mission et al 2006. Thus, although temperature may limit respiration processes in the winter, it is clear from this and previous studies at our site (e.g., Ma et al 2005) that moisture-availability is a greater influence on R s throughout the growing season in this Sierran mixed-conifer forest (Fig.…”

A new carbon and oxygen balance model based on ecological service of urban vegetation

“…The IEA study found that globally, urban area accounts for 67% of energy consumption and 71% of CO 2 emission worldwide (IEA, 2008). Previous researches showed that the carbon flow balance condition of forest ecosystem had an important feedback on global warming (Cox et al, 2000), and the contribution of forest ecosystem in global carbon balance has gained a growing focus from the research world (Lloyd et al, 2002;Kolari et al, 2004). Thus, the importance of urban vegetation to human world was quite obvious.…”