Margarete Watzka

By Margarete Watzka and Ernesto Medina

Mangrove trees of the salt secreting Avicennia germinans and the non-secreting Rhizophora mangle were investigated at the northern coast of Venezuela at a low salinity site (127 mmol kg−1) and two hypersaline sites (1600–1800 mmol kg−1). Leaf sap osmolality and mass/area ratio of both species were positively correlated, while size was negatively correlated with soil salinity. Leaf sap osmolality was always higher in Avicennia and exceeded soil solution osmolality. Salinity increased the concentration of 1D-1-O-methyl-muco-inositol (OMMI) in Rhizophora and glycinebetaine in Avicennia. The latter could make up to 21% of total leaf nitrogen (N). Nitrogen concentration was higher in Avicennia, but subtracting the N bound in glycinebetaine eliminated interspecific differences. Photosynthetic rates were higher in Avicennia, and they decreased with salinity in both species. Leaf conductance (gl) and light saturated photosynthesis (Asat) were highly correlated, but reduction of gl at the hypersaline sites was more pronounced than Asat increasing water use efficiency in both species. Lower values of 13C discrimination at the hypersaline sites evidenced higher long-term water use efficiency. Apparent quantum yield and carboxylation efficiency decreased with salinity in both species. Rhizophora was more sensitive to high salinity than Avicennia, suggesting that glycinebetaine is a better osmoprotectant than OMMI.

Part of the book: Photosynthesis