Monoranjan Ghose

Photosynthesis and water-use efficiency of some mangroves from Sundarbans, India

We studied seasonal fluctuations in the rates of photosynthesis, transpiration, PAR, and stomatal conductance for 16 species of true mangroves from the Sundarbans region of West Bengal. Soil salinity and pH were also measured. Leaf temperatures were almost always higher than the ambient temperature. We observed considerable seasonal (summer vs winter) as well as interspecific variations in photosynthesis, with the highest rates occurring inHeritiera fomes (13.21 pmol m-2s-1) andAvicennia marina (11.8 mol m-2s-1), and the lowest inNypa fruticans (1.56 mol m-2s-1) andCeriops decandra (2.32 pmol m-2s-1), in many species, an abrupt rise in leaf temperature retarded the photosyn-thetic process. In winter, the rate of transpiration and stomatal conductance reached their maxima inA. marina (4.83 mmol ra-2s-1 and 124.23 m mol m-2s-1, respectively) and their mimima inExcoecaria agallocha (1.85 mmol m-2s-1 and 49.19 mmol m-2s-1, respectively). In contrast, the maximum summer readings were recorded in E.agallocha (6.07 mmol m-2s-1 and 192.74 mmol m-2s-1 respectively).

Photosynthesis and Water-Use Characteristics in Indian Mangroves

Photosynthesis and water efflux were measured in different PAR and stomatal conductance in members of Avicenniaceae and Rhizophoraceae. Trend of leaf temperature with irradiance and its effect on photosynthesis were also estimated. In most of the studied species, photosynthesis and stomatal conductance followed similar trends with increase in irradiance. The rate of net photosynthesis and stomatal conductance were higher in members of Avicenniaceae than in Rhizophoraceae. In Avicenniaceae, the optimum PAR for maximum photosynthesis ranged between 1340–1685 (μmol m-2s-1, which was also higher than that of Rhizophoraceae (840-1557 μmol m-2s-1). Almost in all the studied taxa, transpiration and stomatal conductance followed similar trends and reached the maximal peaks at the same PAR value. The range of breakeven leaf temperature was almost the same in both the families (34-36°C in Avicenniaceae and 33.5-36.3°C in Rhizophoraceae), beyond which assimilation rate declined.

Distribution of Mangroves and Soil Parameters in the Lothian Island of Sundarbans, India—A GIS Approach

Tropical mangrove ecosystems are highly productive and provide extensive ecosystem services. This paper analyzes distribution of 21 mangrove species (thirteen true mangroves and eight mangrove associates) in relation to various tidal and edaphic factors. Species density, soil parameters and tidal inundation were explored in 40 sites of the Lothian Island of the Western Sundarbans. Only five species and two soil parameters varied significantly under different tidal inundations. Single-linkage hierarchical classification of species densities generated seven distinct species clusters. Stepwise regression of species densities with soil parameters explained a variation of 42% or higher. Calcium, phosphorus, nitrogen, pH, salinity and sand explained the maximum variation in species densities. Statistical method ‘kriging’ in the Arc GIS generated maps predicting distribution of species densities and selected soil parameters over the island. Maps illustrated highly saline northern mudflat region with a distinct seaward fringe of Avicennia alba and herb Acanthus ilicifolius. Soil nutrients like nitrogen, phosphorus and cations like sodium, calcium and magnesium were concentrated in the northern half of the island. Most of the species were concentrated in the middle- and southern-ridged portion of the island having lower soil salinity.