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Effect of soil water stress on soil respiration and its temperature sensitivity in an 18‐year‐old temperate Douglas‐fir stand
Author(s) -
JASSAL RACHHPAL S.,
BLACK T. ANDREW,
NOVAK MICHAEL D.,
GAUMONTGUAY DAVID,
NESIC ZORAN
Publication year - 2008
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.1365-2486.2008.01573.x
Subject(s) - temperate climate , evapotranspiration , soil water , water potential , environmental science , soil respiration , water content , respiration , productivity , zoology , litter , growing season , atmospheric sciences , ecology , soil science , botany , biology , geology , geotechnical engineering , macroeconomics , economics
We analyzed 17 months (August 2005 to December 2006) of continuous measurements of soil CO 2 efflux or soil respiration ( R S ) in an 18‐year‐old west‐coast temperate Douglas‐fir stand that experienced somewhat greater than normal summertime water deficit. For soil water content at the 4 cm depth ( θ ) > 0.11 m 3 m −3 (corresponding to a soil water matric potential of −2 MPa), R S was positively correlated to soil temperature at the 2 cm depth ( T S ). Below this value of θ , however, R S was largely decoupled from T S , and evapotranspiration, ecosystem respiration and gross primary productivity (GPP) began to decrease, dropping to about half of their maximum values when θ reached 0.07 m 3 m −3 . Soil water deficit substantially reduced R S sensitivity to temperature resulting in a Q 10 significantly < 2. The absolute temperature sensitivity of R S (i.e. d R S /d T S ) increased with θ up to 0.15 m 3 m −3 , above which it slowly declined. The value of d R S /d T S was nearly 0 for θ < 0.08 m 3 m −3 , thereby confirming that R S was largely unaffected by temperature under soil water stress conditions. Despite the possible effects of seasonality of photosynthesis, root activity and litterfall on R S , the observed decrease in its temperature sensitivity at low θ was consistent with the reduction in substrate availability due to a decrease in (a) microbial mobility, and diffusion of substrates and extracellular enzymes, and (b) the fraction of substrate that can react at high T S , which is associated with low θ . We found that an exponential (van't Hoff type) model with Q 10 and R 10 dependent on only θ explained 92% of the variance in half‐hourly values of R S , including the period with soil water stress conditions. We hypothesize that relating Q 10 and R 10 to θ not only accounted for the effects of T S on R S and its temperature sensitivity but also accounted for the seasonality of biotic (photosynthesis, root activity, and litterfall) and abiotic (soil moisture and temperature) controls and their interactions.