Ambient aerosols increase stomatal transpiration and conductance of hydroponic sunflowers by extending the hydraulic system to the leaf surface

Juergen Burkhardt; Daniel Zinsmeister; Anita Roth-Nebelsick; Hubert Hüging; Shyam Pariyar

doi:10.3389/fpls.2023.1275358

Ambient aerosols increase stomatal transpiration and conductance of hydroponic sunflowers by extending the hydraulic system to the leaf surface

Front Plant Sci. 2023 Nov 30:14:1275358. doi: 10.3389/fpls.2023.1275358. eCollection 2023.

Authors

Juergen Burkhardt¹, Daniel Zinsmeister¹, Anita Roth-Nebelsick², Hubert Hüging³, Shyam Pariyar¹

Affiliations

¹ Institute of Crop Science and Resource Conservation, Plant Nutrition Group, University of Bonn, Bonn, Germany.
² Department Palaeontology, State Museum of Natural History Stuttgart, Stuttgart, Germany.
³ Institute of Crop Science and Resource Conservation, Crop Science Group, University of Bonn, Bonn, Germany.

Abstract

Introduction: Many atmospheric aerosols are hygroscopic and play an important role in cloud formation. Similarly, aerosols become sites of micro-condensation when they deposit to the upper and lower surfaces of leaves. Deposited salts, in particular can trigger condensation at humidities considerably below atmospheric saturation, according to their hygroscopicity and the relative humidity within the leaf boundary layer. Salt induced water potential gradients and the resulting dynamics of concentrated salt solutions can be expected to affect plant water relations.

Methods: Hydroponic sunflowers were grown in filtered (FA) and unfiltered, ambient air (AA). Sap flow was measured for 18 days and several indicators of incipient drought stress were studied.

Results: At 2% difference in mean vapor pressure deficit (D), AA sunflowers had 49% higher mean transpiration rates, lower osmotic potential, higher proline concentrations, and different tracer transport patterns in the leaf compared to FA sunflowers. Aerosols increased plant conductance particularly at low D.

Discussion: The proposed mechanism is that thin aqueous films of salt solutions from deliquescent deposited aerosols enter into stomata and cause an extension of the hydraulic system. This hydraulic connection leads - parallel to stomatal water vapor transpiration - to wick-like stomatal loss of liquid water and to a higher impact of D on plant water loss. Due to ample water supply by hydroponic cultivation, AA plants thrived as well as FA plants, but under more challenging conditions, aerosol deposits may make plants more susceptible to drought stress.

Keywords: TPU limitation; VPD; anisohydric; atmospheric drought; hydraulic activation of stomata; leaf hydraulics; proline; wick.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. JB was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – project numbers 193519114 and 446535617. DZ acknowledges funding by Deutsche Bundesstiftung Umwelt (20019/602-35). This work was supported by the Open Access Publication Fund of the Universty of Bonn.