PHOTOSYNTHETICA

Photosynthetica 2006, 44(1):32-38 | DOI: 10.1007/s11099-005-0155-2

Changes in photosynthesis and fluorescence in response to flooding in emerged and submerged leaves of Pouteria orinocoensis

M. D. Fernandez¹

¹ Instituto de Biologia Experimental, Universidad Central de Venezuela, Caracas, Venezuela

In the seasonally flooded forest of the Mapire River, a tributary of the Orinoco, seedlings remain totally covered by flood water for over six months. In order to characterize the physiological response to flooding and submergence, seedlings of the tree Pouteria orinocoensis, an important component of the forest vegetation, were subjected experimentally to flooding. Flooding was imposed gradually, the maximum level of flood including submerged and emerged leaves. After 45 d a severe reduction of net photosynthetic rate (P _N) and stomatal conductance (g _s) was observed in emerged leaves, whereas leaf water potential remained constant. The decrease in P _N of emerged leaves was associated to an increase in both relative stomatal and non-stomatal limitations, and the maintenance of the internal/air CO₂ concentration (C _i/C _a) for at least 20 d of flooding. After this time, both P _N and g _s became almost zero. The decrease in photosynthetic capacity of emerged leaves with flooding was also evidenced by a decrease in carboxylation efficiency; photon-saturated photosynthetic rate, and apparent quantum yield of CO₂ fixation. Oxygen evolution rate of submerged leaves measured after three days of treatment was 7 % of the photosynthetic rate of emerged leaves. Submersion determined a chronic photoinhibition of leaves, viewed as a reduction in maximum quantum yield in dark-adapted leaves, whereas the chlorophyll fluorescence analysis of emerged leaves pointed out at the occurrence of dynamic, rather than chronic, photoinhibition. This was evidenced by the absence of photochemical damage, i.e. the maintenance of maximum quantum yield in dark-adapted leaves. Nevertheless, the observed lack of complementarity between photochemical and non-photochemical quenching after 12 d of flooding implies that the capacity for photochemical quenching decreased in a non-co-ordinate manner with the increase in non-photochemical quenching.

Additional key words: carboxylation efficiency; chlorophyll; internal CO₂ concentration; oxygen evolution rate; photoinhibition; quantum yield; photochemical and non-photochemical quenching; stomatal conductance; tropical forest

Received: December 16, 2004; Accepted: April 11, 2005; Published: March 1, 2006  Show citation