Effects of salinity and sand burial on germination and establishment of Blutaparon portulacoides (St.Hil.) Mears (Amaranthaceae) on backshore of southern Brazil

Abstract

The effect of different salinities on the germination was tested during 40 days in laboratory, using six concentrations of NaCl (0, 45, 80, 130, 170 and 215 mM NaCl) and three concentrations of seawater (25, 30 and 35‰). In addition, the survival and growth of seedlings were tested in five constant salinity regimes (0, 45, 80, 130 and 170 mM NaCl) as well as in five regimes of simulating seawater overwash. The effect of sand burial on the germination was tested during 40 days in the laboratory, using five different depth (0, 1, 2, 4 and 6 cm). Additionally, 100 seedlings (2-weeks old) were planted along the backshore and their survival and sand deposition observed at 5-day intervals, during 30 days. The results showed that total germination declines with increased salinity concentration, the same was observed for lag time. The effects of salinity on seedling growth showed that height and distance between nodes were a more sensitive indicator of salinity stress, showing a gradual reduction in growth with increase of NaCl. Seedlings showed a gradual decrease in survival and dry biomass in relation to the frequency of flooding with seawater. The germination of B. portulacoides seeds decresed significantly at depths greater than 2 cm, and was inhibited at 6 cm. Seedlings showed high mortality at even low sand burial. The results obtained in laboratory on germination and growth of B. portulacoides in salinities above those normal in its natural habitat could explain why it is a dominant species at the backshore. However, sand deposition is a major environmental factor that determines the establishment of new seedlings.

Key words: salt tolerance, seedling growth, dune species, Atlantic coast.