In Situ Leaf Growth Measurements Using Digital Image Analysis
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Plant growth is a broad topic that is of interest in many different research fields from the basics of plant functioning, to agricultural research, and ecology. In this thesis, I first distinguish different aspects of plant growth, and discuss how they are coupled across spatiotemporal scales. I then focus on short term eudicot leaf growth measurements, as this is a topic that is relatively sparsely explored in the literature, despite its importance for plant resource use efficiency and performance. There are methodological challenges to measure leaf expansion, particularly in situ because of adverse environmental conditions. I adopted an existing leaf growth measurement method based on leaf fixation and marker tracking for long term outdoor measurements, and I explored the viability of a custom made stereo vision system for the same task. Using marker tracking, I observed a consistent diel growth pattern with considerable leaf area shrinkage in the morning, re-expansion in the afternoon, and growth at night in the mangrove Avicennia marina. Using stereo vision, I achieved a high correlation of leaf area measurements with a ground truth from scanned leaves, but the accuracy was comparatively low. The marker tracking worked well in the most adverse environment and is a suitable low cost method for in situ leaf growth measurements.