GRASSLAND PRODUCTIVITY AND CARBON DYNAMICS: CONSEQUENCES OF CHANGE IN ATMOSPHERIC CO2, PRECIPITATION, AND PLANT SPECIES COMPOSITION, ...
Location: Grassland, Soil and Water Research Laboratory
Title: Soil-mediated effects of subambient to increased carbon dioxide on grassland productivity
Submitted to: Nature Climate Change
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 8, 2012
Publication Date: September 27, 2012
Citation: Fay, P.A., Jin, V.L., Way, D.A., Potter, K.N., Gill, R.A., Jackson, R.B., Polley, H.W. 2012. Soil-mediated effects of subambient to increased carbon dioxide on grassland productivity. Nature Climate Change. 2:742-746.
Interpretive Summary: Atmospheric CO2 concentrations [CO2] continue to rise in large part due to anthropogenic activities. Many studies have examined the effects of elevated [CO2] on plant growth and ecosystem productivity, but they have not considered the effects of soil type on ecosystem responses to [CO2]. This is an important knowledge gap. Soils differ considerably over short (tens of meters) spatial scales in properties like texture and organic matter content, which determine water and nitrogen availability to support plant growth, and which may limit productivity increases from elevated [CO2]. Furthermore, differences in water/nutrient availability may favor certain plant species over others, and species change may also influence productivity responses to elevated CO2. We found clear differences among soils in productivity gains to [CO2] expected over the next 50-75 years (500 ppm), but with different causes in each case. On the most resource-rich soil, a heavy clay Vertisol, aboveground net primary productivity (ANPP) gains were small, because elevated CO2 caused little increased resource use efficiency in the two dominant grasses (which together accounted for over half the total biomass). However, on a less resource-rich clay, a Mollisol, elevated [CO2] caused a strong linear increase in ANPP, explained mainly by increased dominance of a more water-loving tallgrass species, which gained more physiological efficiency at elevated [CO2] and outcompeted a more drought-adapted midgrass species. On a sandy Alfisol with low water holding capacity, strong linear increases in ANPP were found, but here attributable primarily to increased soil moisture accruing from lower leaf-level water loss at elevated [CO2]. These results suggest that there may be considerable spatial variation in grassland responses to CO2, and some soils will experience threshold species change as the existing species reach the limits of their ability to respond to the changing conditions, and are out-competed by better-adapted species. This spatial variation and species change needs to be accounted for in models predicting future ecosystem properties arising from climate change.
Climate change is likely to cause non-linear responses in ecosystem function because of the complex interactions among multiple resources limiting aboveground net primary production (ANPP). Using a novel experimental facility for imposing a continuous atmospheric CO2 gradient on three contrasting soil types supporting grassland plant assemblages, we have shown that the potential for future ANPP gains differs among these soils, because of differing combinations of limitation by water or carbon assimilation, with little evidence for nitrogen limitation. The potential for primary productivity gains in grasslands due to future increases in atmospheric CO2 will thus vary across the landscape.