Morphological and Physiological Response of the Sand Dune Herb Hydrocotyle bonariensis to High Solar Irradiance

Document Type

Presentation

Publication Date

8-5-2018

Abstract

Presentation given at 103rd Annual Meeting of the Ecological Society of America.

Background/Question/Methods

Plants growing in the coastal sand dune habitat are exposed to a suite of abiotic factors that may impose limitations to growth and reproduction, including high solar irradiance. In general, plants can respond to high solar irradiance through alterations in leaf morphology to reduce sunlight absorption, such as leaf inclination from horizontal, or physiological mechanisms to safely dissipate excess solar irradiance, such as the xanthophyll cycle. Hydrocotyle bonariensis is a clonal, large-leaf herb common to the sand dune community and has been shown to increase leaf inclination over the growing season. The purpose of this study was to examine the role of leaf inclination and the xanthophyll cycle in the response of H. bonariensis to high incident sunlight by comparing leaf-level incident sunlight, leaf chlorophyll fluorescence (as a proxy for photosynthetic efficiency), leaf chlorophyll content, and xanthophyll cycle activity between control inclined leaves and leaves held in a horizontal orientation. Measurements of leaf-level incident sunlight and photosynthetic efficiency were collected every two hours during midday (1000h – 1400h) for inclined and horizontal leaves in June, August, and September, after which leaf samples were collected for subsequent analysis of chlorophyll content by spectrophotometry and xanthophyll pigments using High-Performance Liquid Chromatography.

Results/Conclusions

Incident sunlight on adaxial leaf surfaces significantly increased during midday in both treatments and was significantly greater for horizontal leaves compared to inclined leaves. There was no significant variation in incident sunlight on abaxial leaf surfaces for either treatment with time, but there was significantly greater incident sunlight on abaxial surfaces of inclined leaves compared to horizontal leaves. There was a significant decrease in photosynthetic efficiency during midday for both leaves, and photosynthetic efficiency was significantly lower in horizontal leaves compared to inclined leaves. These results support previous research suggesting that leaf inclination in H. bonariensis functions to reduce sunlight absorption at midday and facilitate photosynthetic gas exchange. However, there was a substantial decrease in photosynthetic efficiency during midday in inclined and horizontal leaves, suggesting that leaves in both treatments experienced photoinhibition during midday. There was no significant difference in total leaf chlorophyll content between inclined and horizontal leaves, indicating that excess absorbed irradiance was safely dissipated to avoid permanent photodamage. Xanthophyll pigment concentrations are currently being analyzed in collected leaf samples and will be compared between inclined and horizontal leaves to further examine the contribution of the xanthophyll cycle to the response of H. bonariensis to high solar irradiance.

Sponsorship/Conference/Institution

103rd Annual Meeting of the Ecological Society of America

Location

New Orleans, LA

Source

https://eco.confex.com/eco/2018/meetingapp.cgi/Paper/74452

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