Phytolith spectra in respiratory aerial roots of some mangrove plants of the Indian Sunderbans and its efficacy in ancient deltaic environment reconstruction Sayantani Das a , Ruby Ghosh b , Dipak Kumar Paruya a , Yi-Feng Yao c , Cheng-Sen Li c , Subir Bera a, * a Centre of Advanced study, Palaeobotany-Palynology Laboratory, Department of Botany, University of Calcutta, 35 Ballygunge Circular Road, Kolkata 700019, West Bengal, India b Birbal Sahni Institute of Palaeobotany, Lucknow 226007, U.P., India c State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing, China article info Article history: Available online xxx abstract This study reports phytolith diversity in respiratory aerial roots of some true mangrove plants for the first time. To identify the signal of phytoliths retrieved from these respiratory roots in the modern deltaic environments, we have analyzed the phytolith contents of pneumatophores and/or pneumatothodes of 13 mangrove species from 7 families inhabiting true mangrove forests, and compared their represen- tation in assemblages of stems and leaves of 108 taxa and 26 surface soil samples collected from different deltaic sub-environments of the Indian Sunderbans along a salinity gradient. The result shows that most of the phytolith morphotypes occurring in these respiratory roots are redundant, having low taxonomic significance, and are produced in the stems of the same or different plants. Our study revealed that despite the morphological symmetry of the phytolith morphotypes, size differences of two morphotypes i.e. blocky polyhedral and blocky elongated bodies can be attributed to discriminate their source of origin reliably. Discriminant function analysis shows that 97.7% of stem and 66.5% aerating root data on blocky polyhedral morphotypes can be correctly classified. Blocky elongated morphotypes can accurately classify 75.7% of stem data and 81.1% of aerating root data. This means that size parameters of certain phytolith morphotypes can successfully discriminate between stem and respiratory aerial root. Study of surface and sub-surface sediments from a late Quaternary profile (4215  35 BP at a depth of 390 cm and 2810  25 BP at a depth of 30 cm) also confirms the conclusions. The implications of these findings lie in distinguishing true mangrove environments from other deltaic sub-environments, as pneumatophores/ pneumatothodes are only produced in plants inhabiting tidal or intertidal sub-environments. The cre- ation of a comprehensive analogue of aerating root phytoliths from the Indian Sunderbans has provided the necessary ground work for interpretation of late Quaternary environmental studies in the region. Ó 2013 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction The world’s most dominant mangrove forest e the ‘Sunder- bans’ is situated in the east coast (21  30 0 e22  30 0 N; 89  12 0 e90  18 0 E) of the Indian sub-continent covering an area of about 10,000 km 2 , of which about 40% fall within the territory of India (21  31 0 e22  53 0 N and 88  37 0 e89  09 0 -E) and the remainder lies in Bangladesh (Fig. 1). The Indian part of the Sunderbans in West Bengal has the largest mangrove cover (78%) of the total deltaic mangrove cover in the country (Untawale and Jagtap, 1991; Mathew et al., 2010). Of 166 species of trees, shrubs and herbs in the Indian part of the Sunderbans, 35 species are true mangrove, 28 taxa are mangrove associates and 7 are obligate mangroves (Naskar and GuhaBakshi, 1987). Mangrove plants of the Sunderbans have their own adaptive mechanisms to withstand extreme salinity. One such is aerating roots, pneumatophores and pneumatothodes, observed in some of the true mangrove taxa (Duke, 1992). These specialized aerial structures enable plants to breathe air in habitats with saline waterlogged conditions. Hence, these respiratory roots are characteristic of the true mangrove species and are strictly restricted within the swampy mangrove or the tidal mangrove forests. * Corresponding author. E-mail address: berasubir@yahoo.co.in (S. Bera). Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint 1040-6182/$ e see front matter Ó 2013 Elsevier Ltd and INQUA. All rights reserved. http://dx.doi.org/10.1016/j.quaint.2013.11.025 Quaternary International xxx (2013) 1e18 Please cite this article in press as: Das, S., et al., Phytolith spectra in respiratory aerial roots of some mangrove plants of the Indian Sunderbans and its efficacy in ancient deltaic environment reconstruction, Quaternary International (2013), http://dx.doi.org/10.1016/j.quaint.2013.11.025