PRS Publications

Soil-mediated effects of subambient to increased carbon dioxide on grassland productivity

Fay, P.A., V.L. Jin, D.A. Way, K.N. Potter, R.A. Gill, R.B. Jackson, and H.W. Polley. 2012. Nature Climate Change 2:742-746

Abstract

Grasslands are structured by climate and soils, and are increasingly affected by anthropogenic changes, including rising atmospheric CO₂ concentrations. CO₂ enrichment can alter grassland ecosystem function both directly and through indirect, soil-specific effects on moisture, nitrogen availability and plant species composition, potentially leading to threshold change in ecosystem properties. Here we show that the increase in aboveground net primary productivity (ANPP) with CO₂ enrichment depends strongly on soil type. We found that the ANPP-CO₂ response of grassland was 2.5 x greater on two soils with higher plant-available soil moisture and where direct CO₂ effects on ANPP were accompanied by indirect CO₂ effects on ANPP mediated through an increase in soil moisture or increased dominance of a productive C₄ grass. Indirect CO₂ effects on ANPP were absent on a third soil that was less responsive to CO₂ (1.6x). Unexpectedly, soil N availability changed little with CO₂ and did not seem to drive responses in ANPP. On the more responsive soils, the more productive grass C₄ was favoured with CO₂ enrichment because of greater photosynthetic efficiency. Our results enhance present models of the controls on ecosystem responses to CO₂ and demonstrate mechanisms by which soils could cause spatial variation in CO₂ effects on ANPP and other ecosystem attributes.