Replicated annual grassland mesocosms contained within glasshouses are being exposed to three patterns of precipitation (i.e., 318, 678, and 1248 mm; applied with alternating wet and dry periods -- these treatments were designed using 30-yr records of rainfall patterns for coastal California to reflect low, median, and high rainfall years) and two temperatures (i.e., ambient and ambient +3 degrees Celsius). The mesocosms contain three plant "communities": Avena barbata, Erodium botrys, and mixed (7 species including Avena and Erodium). The mesocosms contain one of two soils (collected from Hopland and Sedgwick Field Stations, respectively). The mesocosms (154 total) are rooted in 50 x 75 cm schedule 40 PVC cylinders packed with three soil horizons to field bulk density with horizon depths from the field. The mesocosms were instrumented with TDR probes and psychrometers to follow soil moisture content and water potential throughout the seasons.
Biogeochemical (ecosystem) measurements include: nitrification potential, denitrifying activity, rate of gross nitrogen mineralization, rate of gross nitrification, rate of N2O production, soil O2 concentration, soil solution nitrate and ammonia concentrations, and ecosystem CO2 and methane exchange.
Plant indices being measured include: aboveground biomass, root biomass, canopy architecture, partitioning/allometry, fecundity, phenology, whole ecosystem gas exchange, leaf-level gas exchange, water-use efficiency and 13-carbon discrimination, elemental analysis, leaf pigments, enzymes activity, metabolites and expression of genes associated with carbon and nitrogen metabolism.
Soil microbial indices being measured include: microbial biomass (DNA), microbial activity (RNA), prokayotic community composition (phylochip), active prokaryote (rRNA phylochip), AM in roots (copy #), nitrifier numbers (qPCR and amoA DNA), nitrifier "activity" (qPCR and cDNA amoA), and species composition of ammonia-oxidizing bacteria (clone libraries of amoA).