Modeling the Effects of Climatic and CO₂ Changes on Grassland Storage of Soil C

Abstract

We present results from analyses of the sensitivity of global grassland ecosystems to modified climate and atmospheric CO₂ levels. We assess 31 grassland sites from around the world under two different General Circulation Models (GCM) double CO₂ climates. These grasslands are representative of mostly naturally occurring ecosystems, however, in many regions of the world, grasslands have been greatly modified by recent land use changes. In this paper we focus on the ecosystem dynamics of natural grasslands. The climate change results indicate that simulated soil C losses occur in all but one grassland ecoregion, ranging from 0 to 14% of current soil C levels for the surface 20 cm. The Eurasian grasslands lost the greatest amount of soil C (~1200 g C m^-2) and the other temperate grasslands losses ranged from 0 to 1000 g C m^-2, averaging approximately 350 g C m^-2. The tropical grasslands and savannas lost the least amount of soil C per unit area ranging from no change to 300 g C m^-2 losses, averaging approximately 70 g C m^-2. Plant production varies according to modifications in rainfall under the altered climate and to altered nitrogen mineralization rates. The two GCM’s differed in predictions of rainfall with a doubling of CO₂, and these differences are reflected in plant production. Soil decomposition rates responded most predictably to changes in temperature. Direct CO₂ enhancement effects on decomposition and plant production tended to reduce the net impact of climate alterations alone.