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No overall stimulation of soil respiration under mature deciduous forest trees after 7 years of CO 2 enrichment
Author(s) -
BADER MARTIN K.F.,
KÖRNER CHRISTIAN
Publication year - 2010
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.2010.02159.x
Subject(s) - deciduous , soil respiration , environmental science , respiration , forestry , agroforestry , ecology , soil science , biology , botany , soil water , geography
The anthropogenic rise in atmospheric CO 2 is expected to impact carbon (C) fluxes not only at ecosystem level but also at the global scale by altering C cycle processes in soils. At the Swiss Canopy Crane (SCC), we examined how 7 years of free air CO 2 enrichment (FACE) affected soil CO 2 dynamics in a ca. 100‐year‐old mixed deciduous forest. The use of 13 C‐depleted CO 2 for canopy enrichment allowed us to trace the flow of recently fixed C. In the 7th year of growth at ∼550 ppm CO 2 , soil respiratory CO 2 consisted of 39% labelled C. During the growing season, soil air CO 2 concentration was significantly enhanced under CO 2 ‐exposed trees. However, elevated CO 2 failed to stimulate cumulative soil respiration ( R s ) over the growing season. We found periodic reductions as well as increases in instantaneous rates of R s in response to elevated CO 2 , depending on soil temperature and soil volumetric water content (VWC; significant three‐way interaction). During wet periods, soil water savings under CO 2 ‐enriched trees led to excessive VWC (>45%) that suppressed R s . Elevated CO 2 stimulated R s only when VWC was ≤40% and concurrent soil temperature was high (>15 °C). Seasonal Q 10 estimates of R s were significantly lower under elevated ( Q 10 =3.30) compared with ambient CO 2 ( Q 10 =3.97). However, this effect disappeared when three consecutive sampling dates of extremely high VWC were disregarded. This suggests that elevated CO 2 affected Q 10 mainly indirectly through changes in VWC. Fine root respiration did not differ significantly between treatments but soil microbial biomass (C mic ) increased by 14% under elevated CO 2 (marginally significant). Our findings do not indicate enhanced soil C emissions in such stands under future atmospheric CO 2 . It remains to be shown whether C losses via leaching of dissolved organic or inorganic C (DOC, DIC) help to balance the C budget in this forest.