Data set ID:
Increases in woody vegetation and declines in grasses in arid and semi-arid ecosystems have occurred globally since the 1800s, but the mechanisms driving this major land-cover change remain uncerta
Data file information for the following Jornada data set: Pre-dawn water potential for leaves from 5 precipitation treatments
- field data sheets
-Scholander type pressure bombs
Manipulations during the 2007–2008 growing seasons consisted of water levels of PPT relative to ambient: -80%, -50%, control, +50%, +80%, with 12 replicates per treatment.Time constraints to perform ecophysiological measurements on both black grama and mesquite simultaneously led us to measure these variables in four replicate plots for each of the PPT treatments. Plots were 2.5 X 2.5 m, and each was centered around a single mature mesquite shrub that was similar in size to other mesquite on this ecological site (mean height 0.5 m, canopy diameter 1.1 m). Shrubs were surrounded by black grama (mean basal area 11.48 cm2); black grama individuals selected for measurements were >0.75 m from plot edges. Reductions in PPT were achieved via passive rainout shelters; supplementation was achieved via a sprinkler irrigation system. Desired levels of rainfall reduction (-80 % and -50%) relative to ambient were achieved by modifying the number of transparent V-shaped acrylic strips per shelter. A PVC-pipe irrigation system was used at the enhanced PPT plots, which were irrigated the day after PPT events, with an amount of water equal to 50 or 80% of the event. Supplementation occurred during the spring and fall of 2007 and 2008 using PPT that was captured nearby and stored. Control plots received ambient PPT and had neither shelters nor irrigation systems.Leaf ecophysiology was quantified during the 2007 and 2008 growing seasons on dates with contrasting PPT patterns in the days preceding the sampling date. One mesquite and one black grama leaf from each plot (n = 20 plots; 5 PPT treatments X 4 replicate plots/treatment) were measured during the morning on two dates in 2007 (25 July and 18 August) and three dates in 2008 (21 July, 25 July, 13 August). Predawn xylem water potential was quantifed with pressure chambers (black grama: model 1000,with 100 bar capacity; PMS Instrument Co, Corvallis, OR; mesquite: model 2005, Soil Moisture Equipment Corp,Santa Barbara, CA).
QA/QC: N/A Preliminary treatment of data: raw data submitted
Block 2 of Sala's Global Change experiment (LTER Study 278) in Pasture 13
Measurements were taken approximately 3 times per growing season, contingent upon precipitation. This study is complete.