BIOFLow International Research Experience for Students (IRES)

Stomata distribution for wind-dependant, tunable transpiration

​​​​​​​Background.

Like all living organisms, plants must exchange material with their environments, expelling and taking in metabolic by-products and nutrients, respectively. Exchange of oxygen and carbon dioxide necessary for photosynthesis takes place at the leaves, where the two gases diffuse in and out through small pores (stomata). The exchange is entirely passive except for the plants’ ability to open and shut the stomata. Transpiration of water, the driver of internal mass transport in vascular plants, takes place through those the same pores, inherently coupling the two mechanisms. With these constraints, the important function of plant physiology depends on the dynamics of the boundary layer through which gases diffuse. Recent studies have shown that interaction between adjacent pores via the evaporative boundary layer strongly affects the efficiency of exchange[1–3], suggest- ing that stomata size and number density should be subject to evolutionary pressure upon changing environmental conditions, such as a gradual change in environmental gas composition[4]. The thickness of the boundary layer and its effect on leaf conductance should be strongly dependent on surrounding flow[5] and leaf geometry. Plants adapted to conditions of variable water scarcity and flow conditions, lacking the ability to respire without losing water, are therefore likely to have tuned their stomata distribution not for optimal efficiency, but for advantageous wind dependence. Previous studies have considered either uniform distributions of stomata or near-zero flow conditions, or both.

​​​​​​​IRES student involvement.

Dr. King will work with an IRES student on this project. This project will 1) relate the variation in stomata distribution of various species’ leaves to the flow/moisture conditions of their habitats; 2) experimentally explore the exchange performance of non-trivial stomata distribution (eg. nearer to edges or clustered in the interior) and leaf geometry as a function of surrounding airflow. IRES students will build a combined dataset from botanical literature and environmental records to identify species of interest. They will prepare simplified, artificial samples with our 3D printer and laser cutter, using pure ethanol as the evaporative liquid to avoid dependence on atmospheric humidity. They will perform experiments in our custom wind tunnel and precision scale to measure the loss of mass through evaporation. The boundary layer will be experimentally characterized with a specially mounted BME680 environmental sensor. Flow speed, angle of attack, and orientation will be varied as necessary to extract a simple yet realistic abstraction of the design principle responsible for the advantageous performance.

References

  1. G. J. Dow, D. C. Bergmann, and J. A. Berry, “An integrated model of stomatal development and leaf physiology,” New Phytologist, vol. 201, no. 4, pp. 1218–1226, 2014.
  2. P. Lehmann and D. Or, “Effects of stomata clustering on leaf gas exchange,” New Phytologist, vol. 207, no. 4, pp. 1015–1025, 2015.
  3. M. A. Zwieniecki, K. S. Haaning, C. K. Boyce, and K. H. Jensen, “Stomatal design principles in synthetic and real leaves,” Journal of the Royal Society Interface, vol. 13, no. 124, p. 20160535, 2016.
  4. S. Assouline and D. Or, “Plant water use efficiency over geological time–evolution of leaf stomata configurations affecting plant gas exchange,” PLoS One, vol. 8, no. 7, p. e67757, 2013.
  5. E. Shahraeeni, P. Lehmann, and D. Or, “Coupling of evaporative fluxes from drying porous surfaces with air boundary layer: Characteristics of evaporation from discrete pores,” Water Resources Research, vol. 48, no. 9, 2012.