These models synthesize the best understanding of physiological processes and vegetation dynamics, to predict terrestrial carbon fluxes, in

response to future global change factors, including eCO2. Collectively, however, such models exhibit a wide range of sensitivities to future conditions (of CO2 and climate) and exhibit asynchronous behavior under different scenarios (Sitch et al., 2008; Galbraith et al., 2010). The outcomes suggest that our present empirical understanding is insufficient, particularly in terms of soil nutrient limitation Selleckchem Kinase Inhibitor Library and ecosystem responses to eCO2 (Fisher et al., 2013). So far, DGVM predictions for eCO2 induced changes in NPP have only been experimentally validated via comparisons with a limited subset of eCO2 experiments in temperate forests Epacadostat solubility dmso (n = 4) ( Sitch et al., 2008 and Norby et al., 2005). Such forests are widely considered to be constrained by soil nitrogen (N) ( Finzi et al., 2006). At a global scale such conditions are atypical, because many regions

are phosphorus-limited ( Lloyd et al., 2001) and also sequester carbon under very different conditions of temperature, precipitation and sunlight availability. The influence of global variations in environmental conditions appears largely untested by eCO2 research, yet historically DGVMs have only been validated on the basis of this limited number of temperate experiments. To improve our confidence in such models, a better understanding is needed to verify how component plant-soil processes respond to and interact with eCO2 at the global scale. Long-term eCO2 experiments in major global regions for C storage and sequestration

are potentially the most direct way of achieving this. We conducted an appraisal of all eCO2 experiments since 1987, using the following combined search terms in an ISI Web of Science search: “elevated CO2,” “FACE,” “CO2 enrichment” and “ecosystem.” Our specific aim was to consider typical experiments relevant to natural ecosystems, so sources were excluded to remove any investigations using controlled environment Levetiracetam chambers or enclosed greenhouses to simulate eCO2 conditions. Similarly, studies were also excluded if their primary focus was on crop species. Our final synthesis identified 675 papers from 151 unique studies (with a 10 m2–3000 m2 range in total experimental plot area) investigating ecosystem-level responses to eCO2 worldwide, since 1987, when the wider adoption of eCO2 methods first emerged for ecological studies. Of these experiments nearly 44% used FACE technology, whereas others utilized open-top chambers (48%), naturally-occurring CO2 springs (5%) or CO2 systems fitted to the branches of entire trees (3%). The FACE system has the least impact on other growing conditions including microclimate, but is inherently costly and may not be suitable in some locations.