RAINFOR GEM Intensive Plots Manual (pdf) - University of Oxford

ing 106 (=1228.7 cm 3 or cc or mL; just the internal volume V d in the diagram above, not V d +V t because theadapter ring contains the stem collar and this volume will be accounted for in the correction below). A is thearea of exposed soil/tree stem against which the SRC+collar have been placed (for a collar of internal diameter10.6 cm 107 A=3.1416*(0.106/2) 2 =0.00882 m 2 =88.2 cm 2 ). For example, at T a =27°C the calculation might gosomething like:470 − 451 982 0.0012287 44.01* 0.36Ruc=*=0.434 g CO 2 m -2 h -1124 − 86( 27 + 273.15) 0.00882 8. 31432(see this calculation on an Excel spreadsheet in the ‘Respiration equations exercises’ spreadsheet athttp://www.geog.leeds.ac.uk/projects/rainfor/manuals/Exercises/Respiration%20equations.xls). If you aremeasuring soil respiration on sandy soils then there is a possibility this method overestimates CO 2 efflux (seePumpanen et al. 2004), but we currently do not correct for this.Chamber volume correction: The uncorrected CO 2 efflux R uc should be corrected when the SRC-1 is attachedto any extension to the chamber (as it always is in these protocols). In the case of stem and soil CO 2 efflux theadditional volume is the PVC collar sealing the chamber to the soil/stem. In the case of coarse litter CO 2 efflux,it is the same but the volume of the wood piece(s) inside the collar must be subtracted from the collar internalvolume. The volumes of both the collar and the wood pieces may be calculated from the equation for thevolume of a cylinder (3.1416 * (diameter/2) 2 * length) (or see Harmon et al. 1999 for more shapes). Theequation to correct raw fluxes for changes in chamber volume is:Rc= RucV∗d+ VVdaddedwhere R c is the actual soil/stem CO 2 efflux (what we want) and V added is the additional volume (in m 3 ). If soilrespiration is being measured, V added will be the internal volume of the h cm of PVC collar protruding above thesoil surface 108 :(V added for soil CO 2 efflux in cm 3 ) = 3.1416 * (d collar /2) 2 * h(where d collar is the internal diameter of the collar in cm). For example, for 110 mm tubing (external diameter)with wall thickness 2 mm, the internal diameter is d collar =10.6 cm and for h=5 cm V added =441.3 cm 3 .If the stem CO 2 efflux of a tree is being measured using a PVC collar of length h cm 109 affixed to thestem then we use a similar equation:(V added for stem CO 2 efflux in cm 3 ) = (3.1416 * (d collar /2) 2 * h) + V airspacewhere the V airspace accounts for the possible curvature of the stem at the point of collar attachment. If a flatsection of stem was selected for collar installation then V airspace =0 cm 3 , but if not the curvature of the stemsurface will mean that there is some space between the collar and the stem surface.106 From the measurements in the drawing in the footnote above this implies that the top ~4 cm of the grey part of the SRC-1 isoccupied by the fan and other parts. Metcalfe et al. (2009) had 0.001208 m 3 here with a slightly different adapter ring design.107 Metcalfe et al. (2009) had slightly smaller collars of internal diameter 10.3 cm (area 0.0083 m 2 ).108 Measure d collar and h in the field for each collar as there will be variation not only as a result of inconsistent manufacture andcutting but also because of the collar either settling into the soil or rising as a result of soil faunal activities since the previousmeasurement.109 Measure d collar and h in the field for each collar as there will be variation as a result of inconsistent manufacture and cutting.76