Project Number: 6206-11220-004-02
Project Type: Reimbursable

Start Date: Sep 01, 2003
End Date: Feb 28, 2007

Objective:
Our overall objective is to determine effects of rising atmospheric carbon dioxide (CO2) concentration and the predicted decline in summer precipitation on the relative productivities of forb and grass species on mesic grasslands. Species objectives are to test hypotheses that: (1) Deeply-rooting perennial forbs will comprise a greater proportion of aboveground production in plant communities grown in 'deep' soil than in 'shallow' soil and in communities watered to simulate an intense summer drought than in those watered to simulate an 'average' precipitation pattern. (2) CO2 enrichment will reduce evapotranspiration rates, increase soil water content during dry periods, and increase deep drainage of water, and (3) CO2 enrichment will ameliorate negative effects of drought on grasses and increase the contribution of grasses to total production of communities watered to simulate an intense summer drought by slowing the rate of soil water depletion from upper soil layers (<1 m depth) during periods between large rainfall events.

Approach:
Novel elongated chambers will be used to expose intact monoliths of mesic grassland to a continuous gradient in CO2 spanning pre-Industrial to elevated concentrations. Nested within the CO2 gradient will be a factorial arrangement of soils and of watering treatments simulating average and below-average precipitation during summer. Monoliths to which treatments will be applied will be mounted on scales to provide a rigorous accounting of ecosystem water balance. This field experiment is unique in incorporating interactions among three factors - precipitation, soils, and atmospheric CO2 concentration - that determine the water budget and plant composition of grasslands and in providing both for an accounting of ecosystem water balance and for a gradient in atmospheric CO2 that allows examination of non-linear responses of grasslands to past through future CO2 levels.

Project Team

Polley, Wayne - Wayne

Related National Programs

Global Change (204)   Rangeland, Pasture, and Forages (205)