Growth, Foliar Mineral Relations, and Gas Exchange of Mammea americana as Influenced by Salinity
Whole plant growth, foliage mineral content, and leaf gas exchange were measured on Mammea americana seedlings exposed to salinity ranging from 0 to 8 dS·m–1 to determine relative tolerance of this species. In one study, growth measured as leaf area, trunk cross-sectional area, and total dry mass was reduced by 23 weeks of exposure to salinity. Growth of plants exposed to 8 dS·m–1 was ≈30% below that of control plants. Leaf gas exchange was reduced by salinity to a greater degree than the growth variables. Stomatal conductance of plants exposed to 8 dS·m–1 was ≈70% below that of control plants. Plants exposed to 8 dS·m–1 exhibited a seven-fold increase in leaf chloride and 13-fold increase in leaf sodium compared to the control plants. In a second study, 8 weeks of exposure to 8 dS·m–1 reduced net CO2 assimilation and apparent quantum yield to ≈50% of the values for the control plants. Dark respiration was not influenced by salinity. The results indicate that Mammea americana is moderately sensitive to salinity stress.