Supervisors: prof Olevi Kull (2002 - 2007), vanemteadur Anu Sõber
prof Josep Peñuelas (Universitat Autonoma de Barcelona)
Opponent: teadur Albert Porcar-Castell, PhD (Helsingi Ülikool)
Changes in global climate influence growth, species composition and density of plants and thus have a strong effect on global food and timber supplies. Additionally the ecosystem capacity to sequestrate carbon from the atmosphere influences our environment, since the partly human-induced rise in the carbon dioxide concentration of the atmosphere has a strong impact on global climate. Thus the investigations of plant carbon assimilation become more and more relevant. In order to increase the effectiveness of detecting changes in global vegetation, remote sensing methods, measuring optical reflectance of vegetation from space, are extensively used.
During international projects the factors that influence the carbon budget of vegetation and the remote estimations of carbon production were investigated, while this thesis focused on differences in the light use efficiency of plants. The thesis investigated which parameters of plant structure and physiology are most responsive to changes in light environment, and how differences in those parameters affect optical estimations of light use efficiency of vegetation and single leaves. Research on different European shrublands revealed that moist northern shrublands may function as carbon sinks, while dry southern shrublands emit more carbon than is assimilated through photosynthesis. The remote estimations of vegetation parameters, such as light use efficiency, were strongly influenced by differences in vegetation structure. Leaf-level optical estimations of light use efficiency were affected by leaf and canopy structure and physiology as well, while the effect was dependent o!
n plant species. Most responsive to differences in light conditions, appeared to be the distribution of nitrogen between different functional compartments of plants. In conclusion, this study revealed that if light use efficiency of leaves, plants or vegetation is estimated remotely using optical methods, leaf and canopy structure and species-specific differences in light-acclimation strategies must be considered.