UVM Theses and Dissertations
Format:
Print
Author:
Borer, Catherine Hamilton
Dept./Program:
Rubenstein School of Environment and Natural Resources
Year:
2004
Degree:
Ph. D.
Abstract:
Calcium (Ca) is an essential macronutrient in plants, and an important component of cellular structures, physiological processes, and overall forest function. However, widespread anthropogenic calcium depletion is occurring as a result of many processes, including acidic deposition. Direct foliar leaching preferentially depletes physiologically relevant pools of Ca, such as membrane-associated Ca (mCa). Labile apoplasmic Ca is mobilized for physiological responses to numerous environmental stimuli, and mCa may be an important source for this signaling. Thus, mCa depletion could predispose trees to exaggerated injury following even "normal" stress exposure by impairing environmental responsiveness. Work presented in this dissertation uses red spruce (Picea rubens Sarg.) as a model species to further elucidate fundamental processes associated with foliar Ca partitioning as well as impairments and vulnerabilities associated with deficient foliar Ca.
I also assessed changes over time in the relationships among total foliar Ca and specific pools of foliar Ca. Despite seasonal phenology, mCa was consistently lower in trees with deficient total foliar Ca, compared to trees with intermediate and sufficient Ca. A dramatic mCa decline occurred after an environmental cue in foliage with sufficient mCa, but did not occur in deficient foliage. In plants with normally sufficient mCa, depleted mCa after signaling may represent a refractory period, during which physiological responsiveness is muted and plants are vulnerable to damage. In contrast to mCa, chemical extractions showed no difference between sampling dates, demonstrating that these measurements reveal different aspects of foliar Ca physiology. My dissertation research has helped define the physiological basis for foliar Ca deficiency, which depends primarily on availability of labile Ca rather than commonly measured total foliar Ca. Tree health and sensitivity to an array of environmental stresses may be influenced by natural and anthropogenic factors that deplete this labile foliar pool of Ca. My work illustrates vulnerabilities resulting from Ca deficiency, demonstrates essential differences among three methods of assessment, and underscores the importance of biologically relevant cation assessments in biogeochemical research.
I also assessed changes over time in the relationships among total foliar Ca and specific pools of foliar Ca. Despite seasonal phenology, mCa was consistently lower in trees with deficient total foliar Ca, compared to trees with intermediate and sufficient Ca. A dramatic mCa decline occurred after an environmental cue in foliage with sufficient mCa, but did not occur in deficient foliage. In plants with normally sufficient mCa, depleted mCa after signaling may represent a refractory period, during which physiological responsiveness is muted and plants are vulnerable to damage. In contrast to mCa, chemical extractions showed no difference between sampling dates, demonstrating that these measurements reveal different aspects of foliar Ca physiology. My dissertation research has helped define the physiological basis for foliar Ca deficiency, which depends primarily on availability of labile Ca rather than commonly measured total foliar Ca. Tree health and sensitivity to an array of environmental stresses may be influenced by natural and anthropogenic factors that deplete this labile foliar pool of Ca. My work illustrates vulnerabilities resulting from Ca deficiency, demonstrates essential differences among three methods of assessment, and underscores the importance of biologically relevant cation assessments in biogeochemical research.