Productivity overshadows temperature in determining soil and ecosystem respiration across European forests

Abstract

Summary This paper presents CO2 flux data from 18 forest ecosystems, studied in the European Union funded EUROFLUX project. Overall, mean annual gross primary productivity (GPP, the total amount of carbon (C) fixed during photosynthesis) of these forests was 1380 ± 330 gC m−2 y−1 (mean ±SD). On average, 80% of GPP was respired by autotrophs and heterotrophs and released back into the atmosphere (total ecosystem respiration, TER = 1100 ± 260 gC m−2 y−1). Mean annual soil respiration (SR) was 760 ± 340 gC m−2 y−1 (55% of GPP and 69% of TER). Among the investigated forests, large differences were observed in annual SR and TER that were not correlated with mean annual temperature. However, a significant correlation was observed between annual SR and TER and GPP among the relatively undisturbed forests. On the assumption that (i) root respiration is constrained by the allocation of photosynthates to the roots, which is coupled to productivity, and that (ii) the largest fraction of heterotrophic soil respiration originates from decomposition of young organic matter (leaves, fine roots), whose availability also depends on primary productivity, it is hypothesized that differences in SR among forests are likely to depend more on productivity than on temperature. At sites where soil disturbance has occurred (e.g. ploughing, drainage), soil espiration was a larger component of the ecosystem C budget and deviated from the relationship between annual SR (and TER) and GPP observed among the less‐disturbed forests. At one particular forest, carbon losses from the soil were so large, that in some years the site became a net source of carbon to the atmosphere. Excluding the disturbed sites from the present analysis reduced mean SR to 660 ± 290 gC m−2 y−1, representing 49% of GPP and 63% of TER in the relatively undisturbed forest ecosystems.

Soil temperature and biotic factors drive the seasonal variation of soil respiration in a maize (Zea mays L.) agricultural ecosystem

“…There is strong evidence that rates of plant production and SR are linked processes (Raich and Tufekcioglu 2000). The effect of temperature on root respiration is likely to be constrained by the seasonal changes in NPP, because root respiration largely depends on the amount of photosynthates translocated from the aboveground part of the plant (Hö gberg et al 2001;Janssens et al 2001;Curiel-Yuste et al 2004). Recent field experiments have shown that as much as half of the soil respiratory carbon release is derived from recent photosynthate (Hö gberg et al 2001;Steinmann et al 2004).…”

“…Any changes in the inputs of litter and detritus to the soil are likely to affect rates of microbial respiration strongly (Rey et al 2002). Thus, microbial respiration indirectly depends on ecosystem productivity (Janssens et al 2001). Modeling exercises and field studies have shown that the availability of high quality substrate may drive the temperature sensitivity of heterotrophic respiration (Vance and Chapin 2001;Brooks et al 2004;Eliasson et al 2005).…”

Partitioning sources of soil‐respired CO2 and their seasonal variation using a unique radiocarbon tracer

“…4). Several studies indicate a link between soil respiration and plant activity through the phenological control on root respiration fluxes (Hö gberg et al, 2001;Janssens et al, 2001;Reichstein et al, 2003;Curiel et al, 2004). For this forest, a correlation between root growth and leaf area expansion was observed by Joslin et al (2001), with the highest root elongation intensity taking place after the completion of leaf area expansion.…”

Towards operational remote sensing of forest carbon balance across Northern Europe

“…Since AT is strongly correlated to logarithmic ER, an attempt was made to model ER as an exponential function of AT without relying on R 10 . Even though such a model will be able to explain much of the variation in ER at a specific site, the model -which was constructed in the same manner as the GPP model -was unable to capture the respiration magnitudes for the different sites, confirming the findings of Janssens et al (2001) who found AT to control changes in soil respiration within sites but not between sites. For example, the model was able to simulate ER at Hyytiälä 2005 and Asa which exhibits quite similar AT response (Fig.…”