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Evaluating pulse-amplitude modulated fluorometry for landscape scale assessment of photosynthetic characteristics

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Elizabeth F. Belshe (Creator)
Institution
The University of North Carolina Wilmington (UNCW )
Web Site: http://library.uncw.edu/
Advisor
Michael Durako

Abstract: Pulse-amplitude modulated fluorometry (PAM) was evaluated for monitoring the physiological condition of the seagrass, Thalassia testudinum, in Florida Bay. This approach is attractive because it is rapid, non-invasive, and offers quantitative physiological information. Yet, problems arise when expanding sampling from the organismal scale to the landscape scale, due to temporal changes in photophysiology. The magnitude of diurnal variation of photosynthetic characteristics was investigated using Rapid Light Curves (RLC), which measure quantum yield over a range of changing actinic irradiances. In this study, the resulting calculated parameters (alpha and ETRmax) significantly changed diurnally, as was previously found with effective quantum yield. The significance of among basin and year comparisons was also confounded by diurnal variation and rigorous statistical analysis was unable to discern which time of day was best suited for assessing the photophysiological status of T. testudinum. Even though measurements taken with PAM fluorometry exhibited a significant amount of diurnal noise, informative physiological patterns did emerge. The ability to distinguish among basins and see landscape scale trends within the bay gives us an indication that PAM fluorometry may be useful as a monitoring tool. However, in ecosystems where the magnitude of changes are large and occur on much faster timescales than the ecosystem changes that you are trying to measure, the resulting fluctuations may obscure the true physiological signal. Therefore, when using this approach over large spatial and temporal scales diurnal variability must be considered. In order to incorporate the entire temporal and spatial scale two previously proposed methods, the Diel Yield and Diel Rapid Light Curve method, were investigated. Photosynthesis irradiance (P-E) curves were calculating using both methods and the ability of each method to accurately predict the relationship between electron transport and irradiance was explored. It was found that neither method was able to provide consistent estimates of photosynthetic efficiency or capacity. The Diel Yield method frequently produced unrealistic predictions of photosynthetic capacity (rETRmax) and saturation irradiance (Ik). The Diel RLC method produced more reasonable predictions of rETRmax and Ik, but this method had the most difficulty predicting photosynthetic efficiency (alpha) when ambient irradiances were continuously high throughout the day (>Ik). With some further calculations we believe the Diel RLC method can provide an estimate of photosynthetic efficiency and offer a way to reasonably approximate landscape-level photosynthetic characteristics. Because both methods investigated in this study use data generated from RLCs, which have been shown to vary depending on previous light history; diurnal variations do affect estimates of electron transport rates. Therefore, the Diel RLC method does not negate diurnal variation but it does produce a curve that incorporates the changing ambient light environment.

Additional Information

Publication
Thesis
A Thesis Submitted to the University of North Carolina Wilmington in Partial Fulfillment Of the Requirements for the Degree of Masters of Science
Language: English
Date: 2009
Keywords
Fluorimetry, Photosynthesis--Research, Seagrasses--Florida--Florida Bay, Thalassia--Florida -- Florida Bay
Subjects
Seagrasses -- Florida -- Florida Bay
Thalassia -- Florida -- Florida Bay
Fluorimetry
Photosynthesis -- Research