Scirpus maritimus leaf pigment profile and photochemistry during senescence: implications on carbon sequestration.

Leaf senescence is the final phase of the leaf development, comprising several controlled complex physiological, biochemical and molecular events. From February to June it was possible to observe a rapid increase of Scirpus maritimus biomass accompanied by an increase in the overall pigment battery, photosynthetic efficiency and photoprotection capacity. With senescence progressing, the photosynthetic pigments decreased dramatically in a rather equal extent. With the exception of Zeaxanthin (90% decrease), all pigments suffered a 98-100% decreased during senescence. Overlooking the operational PSII quantum efficiency it was possible to observe that it suffered almost no changes during leaf maturation (with the exception of the senescent leaves), whilst the maximum quantum efficiency, showed more evident changes, decreasing with the leaf maturation. This observation coupled with the increased DES index may be an indication that the decrease in the PSII maximum yield may represent a mechanism to down-regulate the photosynthetic electron transport rate compensating the consequent decrease in CO(2) assimilation capacity. This fact allied with a decrease in the minimum light intensity for photosynthesis saturation in senescent leaves, suggest that the requirement for reducing power and photophosphorylation for the dark reaction is inevitably decreased and that photosynthesis in senescent leaves will be saturated.