Physiological Ecology of Psammophytic and Halophytic Plant Species from Coastal Plains in Northern South America

Abstract

Coastal plains of all tropical and subtropical latitudes are the habitat for a number of highly specialized plants able to establish in a range of sandy to clayey soils, submitted to periodical flooding from rainfall and tides, tolerant to large variations of salinity of soils interstitial water, withstanding coastal winds and sea-salt spray, and submitted to yearlong high solar irradiation and day temperatures. In northern South America semi-arid climates predominate in the southern Caribbean coasts from 10 to 15 degrees N, an area that includes from the Goajira peninsula in Colombia to the Paria Peninsula in eastern Venezuela, and most southern Caribbean islands. The functional properties of mangroves (Laguncularia racemosa, Avicennia germinans) and associated halophytes (Conocarpus erectus, Sesuvium portulacastrum and Batis maritima) in seasonal arid coasts reveal the impact of highly seasonal distribution of rainfall affecting photosynthesis and leaf osmotic relations. The soil-plant nutritional relationships of a number of commonly occurring coastal species allowed the characterization of psammophytes and halophytes, based on the Na/K, and Ca/Mg ratios, and their preferential absorption of K over Na. Carbon 13 isotopic analyses showed the C-4 species were well represented within the selected species (Sporobolus virginicus, Atriplex oestophora, Euphorbia mesembryathemifolia) but this photosynthetic metabolism is not the most common. Natural abundance of N-15 indicates that sources of N are enriched in the heavier isotope suggesting that these coastal systems are limited by P but not by N. Mycorrhizal associations were common in most species but intensity of colonization was generally low. The occurrence of micorrhizal associations in true halophytes remains to be assessed.