Drying and wetting of Mediterranean soils stimulates decomposition and carbon dioxide emission: the "Birch effect".
Observations on the net carbon exchange of forests in the European Mediterranean region, measured recently by the eddy covariance method, have revived interest in a phenomenon first characterized on agricultural and forest soils in East Africa in the 1950s and 1960s by H. F. Birch and now often referred to as the "Birch effect." When soils become dry during summer because of lack of rain, as is common in regions with Mediterranean climate, or are dried in the laboratory in controlled conditions, and are then rewetted by precipitation or irrigation, there is a burst of decomposition, mineralization and release of inorganic nitrogen and CO(2). In forests in Mediterranean climates in southern Europe, this effect has been observed with eddy covariance techniques and soil respiration chambers at the stand and small plot scales, respectively. Following the early work of Birch, laboratory incubations of soils at controlled temperatures and water contents have been used to characterize CO(2) release following the rewetting of dry soils. A simple empirical model based on laboratory incubations demonstrates that the amount of carbon mineralized over one year can be predicted from soil temperature and precipitation regime, provided that carbon lost as CO(2) is taken into account. We show that the amount of carbon returned to the atmosphere following soil rewetting can reduce significantly the annual net carbon gain by Mediterranean forests.
Jarvis
Paul
P
School of GeoSciences, The University of Edinburgh, The King's Buildings, West Mains Road, Edinburgh, EH9 3JN, Scotland, UK. margaretsjarvis@aol.com
Rey
Ana
A
Petsikos
Charalampos
C
Wingate
Lisa
L
Rayment
Mark
M
Pereira
João
J
Banza
João
J
David
Jorge
J
Miglietta
Franco
F
Borghetti
Marco
M
Manca
Giovanni
G
Valentini
Riccardo
R
D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism*; D017753:Ecosystem; D019083:Mediterranean Region; D008954:Models, Biological; D012621:Seasons; D012987:Soil; D014197:Trees / Q000254:growth & development / Q000378:metabolism; D014867:Water / Q000378:metabolism*
D012987:Soil; D014867:Water; D002245:Carbon Dioxide