EGU21-13494
https://doi.org/10.5194/egusphere-egu21-13494
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

How does increasing CO2 influence the land-atmosphere exchange of carbon and water in response to soil and air dryness?

Chunhui Zhan1, René Orth1, Markus Reichstein1, Mirco Migliavacca1, Sönke Zaehle2, and Alexander Winkler1
Chunhui Zhan et al.
  • 1Department of Biogeochemical Integration, Max Planck Institute for Biogeochemistry, D-07745 Jena, Germany (czhan@bgc-jena.mpg.de)
  • 2Department of Biogeochemical Signals, Max Planck Institute for Biogeochemistry, D-07745 Jena, Germany

Variability in the photosynthetic uptake of CO2 by plants due to climate variability plays an essential role in modulating the growth rate of atmospheric CO2. In particular water stress induced by the compounding effect of vapor pressure deficit (VPD) and soil moisture anomalies has a large bearing on photosynthetic CO2 uptake, especially in semi-arid areas. The ongoing rise in atmospheric CO2 concentration can influence the water-use efficiency of plants, their carbon assimilation rate, and consequently the global cycles of carbon and water.  However, the extent to which physiological effects of increasing CO2 influence the coupling of VPD, soil moisture, and land-atmosphere CO2 fluxes is currently poorly understood.

In this study we use the terrestrial ecosystem model QUINCY (QUantifying Interactions between terrestrial Nutrient CYcles and the climate system, Thum et al. 2019, GMD) to study CO2-induced changes in the interaction of plant productivity and both soil moisture and VPD. With the sensitivity of stomatal conductance to atmospheric CO2 concentration implemented in the model, we investigate century-long simulations across different climate regimes and biomes. In semi-arid regions we find a positive relationship between anomalies of VPD and gross primary productivity (GPP) at both start and end of summer months, and a negative relationship in the dry period (usually from June to August in boreal summer). This suggests there is a transition in the limiting factor of GPP from energy (compound effect of temperature and radiation) to water and back in the course of one year. The negative correlation between VPD and GPP during the dry period weakens over time with rising CO2, while a stronger positive correlation between soil moisture and GPP becomes apparent. After quantifying and understanding the CO2 effects in these model simulations, we apply our analysis framework to observational data from the FLUXNET site collection to analyze whether we can confirm the model-based findings despite shorter records.

How to cite: Zhan, C., Orth, R., Reichstein, M., Migliavacca, M., Zaehle, S., and Winkler, A.: How does increasing CO2 influence the land-atmosphere exchange of carbon and water in response to soil and air dryness?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13494, https://doi.org/10.5194/egusphere-egu21-13494, 2021.

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