Interactions between topsoil properties and ecophysiological responses of mangroves (Avicennia marina) along the tidal gradient in an arid region in Qatar

Abstract

This study investigated the interactions between topsoil properties and ecophysiological responses of Avicennia marina along the tidal gradient in an arid region in Qatar. In February 2017, three plots were established, each at a distance of 0 m (D0), 50 m (D50), and 100 m (D100) from the inland boundary of a mangrove forest. Soil samples were collected at 0–10-cm depth in each plot to determine the chemical properties, and the density of seedlings, saplings, and trees was measured. Moreover, above- (AGB) and below-ground biomass (BGB) were calculated using an allometric equation for A. marina with the measured diameter at breast height in February 2017. As an indicator of salt stress, chlorophyll fluorescence parameters were measured in October 2017. Salinity (45.60 ppt) and exchangeable sodium percentage (ESP; 29.02%) at D100 were significantly highest. AGB was higher at D100 (41.44 Mg ha–1) than at D0 (0 Mg ha–1) and D50 (7.33 Mg ha–1), and BGB was higher at D100 (44.91 Mg ha–1) than only at D0 (0 Mg ha–1). There was no significant difference in the density of seedlings, saplings, or trees or the chlorophyll fluorescence parameters among the plots. Salt stress was not induced despite the hypersalinity at this site, since A. marina growing in an arid climate can endure strong salinity. Soil pH was highest at D0, followed by at D50 and D100. Organic matter, total nitrogen, available phosphorus, and cation exchange capacity were significantly higher at D100 than at D0 and D50. Higher concentrations of nutrients on the seaward side might result from the tidal gradient and a large input of organic matter and low soil alkalinity.