Altering rainfall timing and quantity in a mesic grassland ecosystem: Design and performance of rainfall manipulation shelters

Global climate change is predicted to alter growing season rainfall pattern s, potentially reducing total amounts of growing season precipitation and r edistributing rainfall into fewer but larger individual events. Such change s may affect numerous soil, plant, and ecosystem properties in grasslands a nd ultimately impact their productivity and biological diversity. Rainout s helters are useful tools for experimental manipulations of rainfall pattern s, and permanent fixed-location shelters were established in 1997 to conduc t the Rainfall Manipulation Plot study in a mesic tallgrass prairie ecosyst em in northeastern Kansas. Twelve 9 x 14-m fixed-location rainfall manipula tion shelters were constructed to impose factorial combinations of 30% redu ced rainfall quantity and 50% greater interrainfall dry periods on 6 x 6-m plots, to examine how altered rainfall regimes may affect plant species com position, nutrient cycling, and above- and belowground plant growth dynamic s. The shelters provided complete control of growing season rainfall patter ns, whereas effects on photosynthetic photon flux density, nighttime net ra diation, and soil temperature generally were comparable to other similar sh elter designs. Soil and plant responses to the first growing season of rain fall manipulations (1998) suggested that the interval between rainfall even ts may be a primary driver in grassland ecosystem responses to altered rain fall patterns. Aboveground net primary productivity, soil CO2 flux, and flo wering duration were reduced by the increased interrainfall intervals and w ere mostly unaffected by reduced rainfall quantity. The timing of rainfall events and resulting temporal patterns of soil moisture relative to critica l times for microbial activity, biomass accumulation, plant life histories, and other ecological properties may regulate longer-term responses to alte red rainfall patterns.