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

3.3 Components of soil CO 2 efflux (the Partitioning Experiment)The idea for this comes from the DIRT experiment at Harvard Forest, USA (Nadelhoffer et al. 2004), however,instead of applying the treatments over large areas of forest we apply it in small collars inserted into the forestfloor (Metcalfe et al. 2008a). Note that all roots are removed during installation so all collars are initially rootfree(corresponding to the “no roots” and “no inputs” treatments of the DIRT experiment) and the differencebetween rows 2 and 3 (protocol option #1) only develops over time in this design. This design includes a rootfree-but-not-mycorrhizae-freetreatment 64 (row 2) absent from the DIRT experiment.Prepare the mesh collars (row 2, collars 2a-2c) by cutting two 3 cm × 3 cm windows (if square windows are not possible, 3.39 cmdiameter circular windows 65 ) along two opposite sides of twelve 40 cm long collars (i.e. four 3 cm × 3 cm windows on each collar 66 ).The upper rim of the first window should begin exactly 5 cm along the collar, each window should be separated by 5 cm (if square, or4.23 cm if circular) along the collar so that the windows are contained within the top 16 cm of the collar. Now cut the fine mesh into 5cm × 5 cm squares, line the perimeter of the windows with glue/sealant and place a fine mesh square onto it. Do not extend the meshover the lower ends of the collars.64 n.b. (1) In this experimental design only ectomycorrhizae that grow fungal mycelia across the soil matrix are considered and (2) It iswell known that many mycorrhizae are symbiotic with particular species or genera of plants, but this design measures only the overalleffect of all mycelial networks present in the soil without division into mycorrhizal species (see e.g. Cornelissen et al. 2003 for asummary of all types of mycorrhizae).65 If not possible, choose a diameter as close as possible and modify the spacing so that they remain positioned within the top 16 cm.66 = 4*9 cm 2 out of 35*2*3.1416*(11/2) cm 2 suface area below ground so these ‘windows’ collars reduce soil exposure by ~97%, butmost roots are in the top few cm of the soil so in reality the reduction in root exposure is much smaller. Note that the bottom of thecollar is not covered by mesh (the end of the collar away from the windows) because that will be in deep soil with few roots.54