title: Wind influence on plants: ecophysiological, biomechanical, and aerodynamic aspects
Creators: name: Zhdanov, Oleksandr
Publisher: name: University of Glasgow
Year: 2021
Subjects: subject: Arabidopsis, wind-plant interaction, mechanical properties, dynamic testing, anemotropic response, thigmotropic response, thigmomorphogenesis, wind, biomechanics, bluff bodies, aerodynamic coefficients, succulent-inspired cylinders, cactus-inspired cylinders.

description: Wind has a wide range of effects on plants: from wind-induced damage in the form of lodging to an increased rate of photosynthesis. Climate models predict that plants will be exposed to elevated wind conditions in many regions around the world due to global warming. To be able to attenuate the negative impact of changing wind patterns on plants, it is necessary to expand our understanding of wind-plant interaction. In this thesis two different aspects of wind-plant interaction are investigated. In the first part, the acclimation response of a model plant, Arabidopsis thaliana, to mechanical stress in the form of continuous wind of a constant speed is explored. A bespoke wind tunnel, suitable for continuous growth of plants, was developed. For the mechanical characterisation of Arabidopsis stems a new multiple resonant frequency method was devised and validated. As a result of the wind treatment, the plants exhibited a positive anemotropic response. This response was documented for the first time in any plant system. Overall, the wind-induced thigmomorphogenetic changes and alterations in the mechanical properties of the primary inflorescence stem were considered to be adaptive to this type of mechanical stress. The mechanical properties can be related to modification in the anatomical tissue organisation and ion content, providing possible sources of the observed changes. In many experiments reported in the literature, wind is mimicked by brushing treatments. In this project, the validity of this approach was investigated by conducting a comparison of the response of Arabidopsis to uni- and bidirectional brushing treatments with the wind-induced changes. While some of the changes to Arabidopsis morphology can be reproduced by matching the vectorial influence of wind and brushing treatments, the changes in the mechanical properties occurred in opposite directions. The unidirectional brushing treatment also evoked a positive tropic response, which can be considered thigmotropic and has been demonstrated for the first time in Arabidopsis shoot. The second part of this thesis explores the aerodynamics of succulent-inspired cylinders using numerical and experimental techniques. Succulents and cacti are, probably, the most well-known examples of convergent evolution in plants, where two different species have independently developed similar traits and features in similar environments but in different parts of the Earth. Investigations inspired by the Saguaro cactus reported in the literature, showed that the presence of ribs on its trunk, among other functions, helps to reduce the aerodynamic forces and decreases unsteady force fluctuations. In contrast to Saguaro, which can have up to 30 ribs, succulents tend to have a considerably lower number of ribs, with only three and four ribs found in many species. This work investigates whether succulent-inspired bluff bodies with a low number of ribs show similar aerodynamic benefits as cactus-shaped cylinders with many ribs. 2D URANS simulations were carried out for two cylinders with three and four ribs, which resemble the succulents Euphorbia trigona and Euphorbia abyssinica, respectively, at Reynolds number 20,000. The succulent-inspired cylinder with four ribs was also investigated using wind tunnel tests with Reynolds numbers ranging from 50,000 to 150,000. For both studied cylinders, a strong angle of attack dependence of all aerodynamic properties was found. For the four-ribbed cylinder no Reynolds number dependence of these properties was observed within the tested range. Overall, succulent-inspired cylinders with a low number of ribs show some aerodynamic advantages in terms of reduction of the mean drag coefficient and the Strouhal number, albeit over a limited range of angles of attack.