Plant functional traits can be successfully used to understand plant ecological strategies and to predict plant responses to a changing climate. Rising sea-level is a major consequence of climate change and people have studied how it affect coastal communities. However, limited work has been conducted on mangrove plants and their plant functional traits despite being among the most stressed ecosystems. Mangroves perform a number of important ecosystem services, including coastal protection. But will mangroves persist in the face of sea-level rise, which is one of the greatest climatic threats to mangroves. Whilst there is the obvious threat of mangroves drowning from increased sea-level, there are also cryptic changes in sediment geochemistry. These changes may have significant implications to the community structure and functional diversity of the mangrove ecosystem; especially in areas where zonation of species based on geochemical gradients occur. Here we use five sedimentary islands of Ashtamudy Lake, southwest coast of Kerala, India, to assess how mangrove ecophysiology is affected by rising sea-levels. We examined community structure, soil geochemistry, lake waterhydrology, leaf functional traits and the stress level or functional status of the mangrove plants. We looked for trait variation across species, mangrove zones and plant growth forms and salt tolerance mechanisms.
Results/Conclusions
Ashtamudy Lake sedimentary islands have found to be submerged for most of the time a day during both low and high tide times. Our results show that the islands lack the characteristic geochemical zonation pattern of mangrove soils. Although the mangrove plant species inhabiting these islands are known to commonly exhibit high zone specificity, we observed that under homogenous geochemical situations they grow in a mixed assemblage with no identifiable zonation. Different leaf functional traits showed higher interspecific diversity, however ecological strategies of different species converged under the homogenous geochemical conditions. Overall there was a loss in leaf functional trait variation among different plant functional types. Chlorophyll fluorescence measurements have proven that mixed growth of mangroves within the same geochemical zone has not affected their fundamental physiological process. The study suggests that mangroves have the capacity to adapt to changing geochemical environments under risen sea-level scenarios, however ecosystem service provision may alter as mangrove ecosystems shift from monospecific zones to mixed assemblages.