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Updated: Mar 19, 2026

A CO2 Concentration Gradient Facility for Testing CO2 Enrichment and Soil Effects on Grassland Ecosystem Function
Published on: November 21, 2015
Impacts of warming and elevated CO2 on a semi-arid grassland are non-additive, shift with precipitation, and reverse
K E Mueller1, D M Blumenthal1, E Pendall2
1Rangeland Resources Research Unit, Agricultural Research Service, United States Department of Agriculture, Fort Collins, CO, 80526, USA.
Abstract:
It is unclear how elevated CO2 (eCO2 ) and the corresponding shifts in temperature and precipitation will interact to impact ecosystems over time. During a 7-year experiment in a semi-arid grassland, the response of plant biomass to eCO2 and warming was largely regulated by interannual precipitation, while the response of plant community composition was more sensitive to experiment duration. The combined effects of eCO2 and warming on aboveground plant biomass were less positive in 'wet' growing seasons, but total plant biomass was consistently stimulated by ~ 25% due to unique, supra-additive responses of roots. Independent of precipitation, the combined effects of eCO2 and warming on C3 graminoids became increasingly positive and supra-additive over time, reversing an initial shift toward C4 grasses. Soil resources also responded dynamically and non-additively to eCO2 and warming, shaping the plant responses. Our results suggest grasslands are poised for drastic changes in function and highlight the need for long-term, factorial experiments.
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