Fluorescence parameters, chlorophyll concentration, and anatomical features as indicators for flood adaptation of an abundant tree species in Central Amazonia: Symmeria paniculata

Abstract

Symmeria paniculata is a common, evergreen tree species from the lowest part of the flooding gradient in blackwater inundation forests in Central Amazonia (Brazil) which does not shed submerged leaves. Chlorophyll a fluorescence was measured regularly in non-submerged and submerged leaves of different age classes in 1999–2000. Measurements at up to 8 m under the water were performed in both years. Chlorophyll concentration was determined in the leaves of different age classes; the older leaves having experienced submergence of several months. The F v/ F m values (‘current photochemical capacity’ of photosystem II (PSII)) in non-submerged leaves and in those submerged at 0–1 m depth were not correlated with the changing water levels and remained above the lower limit of natural variation of healthy leaves (>0.66), indicating an undamaged photochemical apparatus. Younger leaves showed higher F v/ F m values than older leaves which in turn showed higher values than in currently submerged leaves. Leaves submerged in darkness (1–7 m depth, up to 163 days of submergence at the time of measuring) showed F v/ F m values between 0.7 and 0.4, showing a negative correlation with the duration of submergence. The recovery of these F v/ F m values to mostly ≥0.7 during falling water levels apparently took place when still underwater. ‘Rapid light curves’ of leaves submerged at >1 m depth revealed that the PSII started with electron transport when illuminated. However, the electron transport was apparently inhibited shortly after the start. A negative correlation was found between the inhibition of electron transport and the depth/duration of submergence. Chlorophyll concentration was significantly correlated with leaf age, i.e. long-term submergence did not affect this pattern. Comparison of anatomical and morphological leaf structures with other Polygonaceae revealed that S. paniculata follows the general pattern of the family, i.e. they did not appear to be related to particular floodplain conditions. However, several features such as thick epidermis cells and cuticula, cuticular wrinkles, epicuticular waxes, raised stomatal rims, and sunken stomata should facilitate the survival under floodplain conditions.