Degree

Doctor of Philosophy (PhD)

Department

Renewable Natural Resources

Document Type

Dissertation

Abstract

Light acts as a complex signal, influencing various plant physiological, phenological, and morphogenetic traits. While previous studies have explored the effects of varying light levels on branch growth and survival, the underlying mechanisms of branch mortality under shade conditions remain poorly understood, hindering our understanding of canopy dynamics. In this study, I imposed contrasting shade conditions on Pinus taeda branches and investigated the physiological processes of shade-induced mortality in these. The objectives were to (1) evaluate the dynamic changes in photosynthesis and water relations of these branches, (2) investigate the effect of shading treatment on the hydraulic properties of the branches, (3) investigate the potential of using leaf reflectance for estimating shade-induced changes in key photosynthetic traits, and (4) explore the linkage between physiology and shade-related mortality in these branches. In January 2022, prior to spring bud burst, shade treatments were applied on branches on the fifth whorl from the top of selected trees. Treatments of no shade (0%), 30% shade, and 60% shade were randomly assigned equally to the branches. Monthly measurements of the photosynthetic light response curve (LRC), sap flow, water potential, and leaf reflectance of the branches were conducted. Xylem hydraulic conductivity and storage carbohydrate were also quantified at the end of the growing season. Results showed the dominance of carbon dynamics and efficient resource utilization in branch mortality. Shading treatment significantly reduced stomatal conductance, sap flow, and hydraulic conductivity. Leaf reflectance spectroscopy effectively accounted for shade-induced changes in photosynthetic traits. Branches undergoing mortality exhibited significant decrease in assimilation at light saturation, light saturation point, light compensation point, and dark respiration.

Date

7-7-2024

Committee Chair

Dean, Thomas J.

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