Decoupling of stomatal CO2 and H2O fluxes by hygroscopic particles

• Applicant: Privatdozent Dr. Jürgen Burkhardt
• Subject Area: Plant Physiology ; Ecology and Biodiversity of Plants and Ecosystems ; Plant Cultivation, Plant Nutrition, Agricultural Technology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 446535617

Higher plants take up CO2 by diffusion via small openings on the surfaces of leaves, the stomata. Simultaneously, water vapor is lost along the same pathway, driven by atmospheric vapor pressure deficit (VPD). Stomatal aperture determines the fluxes of both gases. For decades, the mutual scaling between the fluxes of water vapor and CO2 has been a central part of all important gas exchange models – recognizable from the factor 1.6, which is the ratio of the respective diffusion constants. The correctness of this assumption is brought into question by the role of deposited aerosols on the leaf surface. Hygroscopic particles dissolve within the humid leaf boundary layer, forming thin liquid films that enter substomatal cavities and link the leaf surface with the apoplastic water. By this “hydraulic activation of stomata” (HAS), the stomata convey liquid as well as vapor phase water from leaf interior to the atmosphere. We have shown that even moderate air pollution produces significant effects, on daytime stomatal transpiration, on minimal night-time conductance, and on the relationship between transpiration and stomatal aperture. As climate-change increases VPD, this effect may become more significant, causing declines in water use efficiency and drought tolerance, and making models based on scalability of CO2 and H2O unreliable.In this proposal, the HAS impact on gas exchange and hydraulics will be quantified in lab, greenhouse, and open field experiments, using both isohydric and anisohydric species, which have been shown to respond differently to aerosol deposition. Aerosol amendment and aerosol exclusion techniques will be used as experimental manipulations, along with state of the art gas exchange, optical and isotope techniques. The results will be important in advancing understanding of plant/atmosphere interactions at scales from guard cell to extensive canopy.

• DFG Programme: Research Grants