Submitted to: Ecological Society of America Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/7/2003
Publication Date: 8/3/2003
Citation: MORGAN, J.A., PATAKI, D.E., GRUENZWEIG, J., KORNER, C., NILAUS, P., POLLEY, H.W., NOWAK, R., NEWTON, P. 2003. GRASSLAND PRODUCTIVITY RESPONSES TO RISING ATMOSPHERIC CARBON DIOXIDE ARE DRIVEN PRIMARILY BY WATER RELATIONS. ECOLOGICAL SOCIETY OF AMERICA PROCEEDINGS. p. 243. Abstract. Interpretive Summary:
Technical Abstract: Increases in CO2 and other trace gases are implicated in global warming that occurred in the past century, and are predicted to cause substantial further increases in temperature and alter precipitation patterns in this century. However, the direct effect of CO2 on plant and soil responses may be just as important, and in some cases, more important than their predicted responses to climatic change. Thus, an understanding of how ecosystems respond directly to rising CO2 concentrations is key to predicting their future functioning and impacts in a CO2 enriched world. A number of field and microcosm CO2 enrichment studies have now been completed in natural and semi-natural grassland ecosystems, and a survey of the pertinent literature revels a wide range of responses to increases in CO2, from no production responses in alpine grasslands or for wet years in the sub-humid tallgrass prairie to consistent and substantial production responses every year in semi-arid shortgrass steppe. What could explain such variable responses to CO2 in various grassland ecosystems? We propose that most of the variation in grassland production to CO2 may be accounted for by variability in precipitation and soil/plant water dynamics, with production being enhanced relatively more by increased CO2 in drier than in wet systems (or years). To evaluate this notion, experimental results from several CO2 enrichment studies from contrasting natural or semi-natural grasslands (temperate and Mediterranean grasslands, tallgrass prairie, shortgrass steppe) and one desert ecosystem were compared. We found that relative aboveground plant biomass enhancements due to increasing CO2 concentrations were generally stronger as annual precipitation declined, and that these biomass enhancements were associated with increases in soil and/or plant water status. The results suggest that CO2-induced production responses in natural and semi-natural grasslands may be understood moderately well by considering only the effects on plant/soil water relations.