Extreme climatic events down-regulate the grassland biomass response to elevated carbon dioxide

Naiming Yuan,Jürg Luterbacher,Christoph Mueller,Gerald Moser,Joerg Bendix,Wolfgang A Obermeier

doi:10.1038/s41598-018-36157-x

Abstract

Terrestrial ecosystems are considered as carbon sinks that may mitigate the impacts of increased atmospheric CO2 concentration ([CO2]). However, it is not clear what their carbon sink capacity will be under extreme climatic conditions. In this study, we used long-term (1998–2013) data from a C3 grassland Free Air CO2 Enrichment (FACE) experiment in Germany to study the combined effects of elevated [CO2] and extreme climatic events (ECEs) on aboveground biomass production. CO2 fertilization effect (CFE), which represents the promoted plant photosynthesis and water use efficiency under higher [CO2], was quantiffied by calculating the relative differences in biomass between the plots with [CO2] enrichment and the plots with ambient [CO2]. Down-regulated CFEs were found when ECEs occurred during the growing season, and the CFE decreases were statistically significant with p well below 0.05 (t-test). Of all the observed ECEs, the strongest CFE decreases were associated with intensive and prolonged heat waves. These findings suggest that more frequent ECEs in the future are likely to restrict the mitigatory effects of C3 grassland ecosystems, leading to an accelerated warming trend. To reduce the uncertainties of future projections, the atmosphere-vegetation interactions, especially the ECEs effects, are emphasized and need to be better accounted.

Highlights

Atmospheric carbon dioxide concentration [CO2] has increased substantially since industrialization and is projected to rise by 40% from approx. 400 ppm in early 2017 to 550 ppm by 2050 (RCP8.5 scenario)[1,2]
We investigated the combined effects of extreme climatic events and elevated [CO2] on aboveground biomass production
Rather than estimating impacts from the changes of mean climate conditions, we analyzed the effects of single extreme events, which may better reveal the response of biotic system to climate drivers

Summary

PFG Total

Due to the low [CO2] enrichment in 2013, together with the extreme cold events, an even lower ES was found in 2013 than in 2012 (Fig. 2a), indicating a combined effect of low [CO2] enrichment and ECEs. Similar results were found for the grass biomass (Fig. 2b). If we remove the potential effects of extremely low [CO2] enrichment, and classify the ES changes (compared to the previous year) from 1999–2011 into two groups according to the occurrence of ECEs, the ES changes were well separated (Fig. 3a,b). While for years with ECEs (2003 and 2010), the slope decreased, vanished, or even became negative, suggesting smaller CFEs under the stress of ECEs. Similar results were obtained for the grass biomass (Fig. S11). Statistically significant and pronounced differences between the CFEs in years without ECEs (2002 and 2009) compared to years with ECEs (2003 and 2010) were observed

Discussion and Conclusion

Materials and Methods

Findings

Additional Information