Fluorescence signatures applied to climate change effects: case studies with Mediterranean oak ecosystems

In Mediterranean-Type Ecosystems (MTE), the photosynthetic apparatus of plants are exposed to long summer droughts and high or low temperatures. Evergreen oak species are dominant in landscapes of countries surrounding: the Mediterranean sea plus parts of California and constitute large shrublands and woodlands. Some hypotheses have been advanced to explain their distributions and comparative advantages. Many of the major distributional trends may be explained by considerations on the carbon balance. Consequently, a detailed knowledge of the effects of such stresses on the carbon balance of oak ecosystems is needed both to explain the today distribution of these species and to anticipate their boundary shifts as a consequence of climatic changes. The authors mainly focus on the electron transport properties, because the photosynthetic rate of oak canopies is primarily light limited. Indices derived from the pulse amplitude modulation method were used in order to characterise the PSII photochemical efficiency and to assess the main parameters of light energy conversion. The authors present results concerning: (1) the extent in which stress factors other than light depress photosynthetic capacity in evergeen oak species grown in ambient and 2×CO₂ atmosphere, (2) the spatial variation of photosynthetic capacity controlled by regional climatic gradient, and (3) its depth-distribution within MTE canopies