Spatio-temporal dynamics of chlorophyll fluorescence in a semi-arid Mediterranean shrubland

We examined the spatio-temporal variations of chlorophyll fluorescence on a semi-arid Mediterranean shrubland in SE Spain during the 1998-1999 period. We performed the study on three species (Quercus coccifera, Pistacia lentiscus and Pinus halepensis) in two sites with contrasted slope aspect (north/south) located within a small distance from each other. Our main objectives were to assess the effect of slope aspect on the chlorophyll fluorescence features of these species, and to evaluate how this effect is influenced by temporal variations in climatic conditions. The results showed the presence of consistent higher values of maximum efficiency of photosystem II (F_v:F _m) in the north-facing slope at both predawn and midday throughout the study period, but with differences in patterns between the different species. For all species, midday values of F_v:F_m were considerably lower than predawn ones at the south-facing slope throughout 1999. For all species, and over the course of the day, the increase and subsequent decrease in radiation was closely followed by a pronounced decrease and subsequent increase of effective quantum yield of photosystem II, but it was less pronounced in the north-facing slope. Our results show how small-scale spatial differences in climate associated with slope aspect cause pronounced differences on the chlorophyll fluorescence features of shrubs. These differences could have important consequences for carbon assimilation and storage and for vegetation dynamics in Mediterranean semi-arid shrublands.