J. Botan. Soc. Bengal 70(2) : 119-124 (2016), ISSN 0971-2976
© Botanical Society of Bengal, Department of Botany, University of Calcutta, Kolkata 700 019, India
Diversity and distribution of polylobate phytoliths in Apluda mutica L., Oplismenus compositus (L.) P. Beauv. and Themeda arundinacea (Roxb.) A. Camus Madhab Naskar1,2, and Subir Bera1* 1 Centre of Advanced Study, Palaeobotany–Palynology Laboratory, Department of Botany, University of Calcutta, 35, Ballygunge Circular Road, Kolkata 700019, India 2 Department of Botany, Sonarpur Mahavidyalaya, Kolkata-700149, India Received : 03.10.2016
Accepted : 19.10.2016
Published : 30.12.2016
This article presents morphological diversity of diagnostic polylobate phytoliths from three exclusively high polylobate yielding grasses Apluda mutica L., Oplismenus compositus (L.) P.Beauv. and Themeda arundinacea (Roxb.) A.Camus from deltaic West Bengal. Finer morphological characters of polylobates isolated from these taxa were documented and utilised to classify into 27 subtypes. Polylobate sub-morphotypes were further used as taxonomic tool to differentiate these taxa. Correspondence analyses also confirmed the taxonomic potential of the polylobate sub-morphotypes. Moreover, the documented polylobate diversity emerged as a signal for moist and shady habitat conditions. This report may strengthen the efficacy of polylobate phytolith as an adjunctive taxonomic tool as well as in understanding the past environment interpretations. Key words: Polylobate phytolith, taxonomic potential, past environment
INTRODUCTION The hydrated silica (SiO2 , nH2 O) micro-particles, deposited in plant tissues are variously known as phytolith, plant opal, opal silica etc. The precipitated amorphous silica within the cell interior adopts diverse forms. Although phytolith formation takes place in a wide range of plant taxa, they are particularly diverse, and abundant in grasses (Rovner, 1971; Piperno, 1988; Mulholland, 1989). The extreme resistance to any physical, chemical or biological degradation and diagnostic potential of grass silicomorphs makes grass phytolith analysis an important microfossil technique in palaeovegetational, palaeoecological and archaeobotanical studies. (Blackman, 1971; Twiss, 1987; Barboni et al., 1999). *E-mail:
[email protected]
Among varied morphotypes produced by grasses, the short cell phytoliths (GSCP) are the most significant whereas other phytoliths produced in the epidermis like elongate, hair cells etc. usually have low taxonomic value. Among the GSCP, lobate phytoliths are the most diverse and widely distributed morphotypes. Lobate phytoliths can be classified into three types: bilobate (having two lobes connected by a shank usually at the central portion), polylobate (consist of more than two linearly arranged lobes) and quadra-lobate (consist of four distinct lobes usually with equal dimensions and arranged side by side) also described as ‘‘cross’’ phytoliths (Twiss et al., 1969; Piperno, 1988; Mulholland and Rapp, 1992; Pearsall, 2000). Variations and significances of bilobates and quadra-lobates have been documented by many workers from various grass taxa from different parts of the world (Lu and Liu, 2003b; Gallego and Distel, 2004; Fahmy, 2008). On
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the contrary, studies on variability, distribution, frequency and importance of polylobotate phytoliths are very rare and scanty (Fahmy, 2008; Neuman et al., 2016). Considering the paucity of polylobate phytolith data, this study was undertaken to find out the predominant polylobate producing grasses and document the diversity, distribution and frequency based attribute of various polylobate morphotypes along with determining their significances. As a preliminary step, the investigation was carried out on grasses of deltaic West Bengal, which reveal the predominance of three panicoid grasses (Apluda mutica, Oplismenus compositus and Themeda arundinacea) over another 107 studied grass taxa (Oryzoideae- 4 spp., Bambusoideae- 8 spp., Pooideae- 1 sp., Aristidoideae1 sp., Panicoideae- 63 spp., Arundinoideae-2 spp., Chloridoideae-28 spp.) in terms of their polylobate production frequencies.
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in the solution. To wash the oxidized samples, centrifugation was done at 2000 rpm for 10 min, and the supernatant was decanted. After several cycles of distilled water wash and centrifugation, the samples were treated with 95% ethanol to clear the supernatant. The residue containing phytoliths were stored in vials. Slides were prepared using polyvinyl alcohol and samples mounted in DPX for photomicrography, and in distilled water for counting. At least 400 phytoliths were counted for every sample. Light photomicrography was carried out at × 450 magnifications using a Zeiss Axioskop microscope. Scanning Electron Microscopy of selected phytolith morphotypes were done using Scanning Electron Microscope (Carl Zeiss – Evo 40) at the Center for Research in Nano Science and Nanotechnology (CRNN) of University of Calcutta, Kolkata. RESULTS AND DISCUSSION
MATERIALS AND METHODS Principal phytolith spectra Collection of samples Reported three grasses were collected along with another 107 grass taxa mainly from lower part of matured delta and active delta i.e. from the Sundarbans mangrove and adjoining areas of deltaic West Bengal. Leaf blades, inflorescences, and culms from each of the taxa were collected at the end of their annual growing cycle, for better representation of phytolith composition at the time of incorporation into the soil. Phytolith extraction, counting, and study Phytoliths were extracted from leaves, culms, and inflorescences of the studied taxa. For identification of grasses we consulted the Central National Herbarium (CAL), Botanical Survey of India. Fresh plant tissues were taken in a beaker for each collected sample and washed with distilled water in a water bath to remove the adhering particles. After cleaning, the plant tissues were dried at 50 °C–60 °C in an oven. Dried plant tissues were taken in test tubes and oxidized with Schulze’s solution (conc. HNO3+NaClO3 in 3:1 ratio) in a hot water bath. The samples were stirred frequently and a small amount of conc. HNO3 and NaClO3 was added when the reaction stopped. The samples were then allowed to cool and fresh conc. HNO3 was added to dissolve the extra NaClO3 present
After comprehensive study of all the collected 110 grasses, these three grasses emerged as the most prolific polylobate phytolith producers. Only these three grass taxa yield nearly half or more than half of their total phytolith (Apluda mutica - 51.63%, Oplismenus compositus - 48.62 %, Themeda arundinacea - 55.11 %) as polylobates. Different subtypes of bilobates were also isolated in significant frequencies (Apluda mutica -27.08, Oplismenus compositus -28.52 %, and Themeda arundinacea - 31.39 %. Cross, trapeziform and elongate morphotypes were retrieved in moderate to low frequencies. They also produce two horned rondel, ellipsoid rondel, keeled rondel, others type (hair cell, prickle cell, stomate etc.), long saddle (only Oplismenus compositus), flat tower (only Apluda mutica), three horned rondel (only Oplismenus compositus), pyramidal rondel (only Oplismenus compositus), oval rondel (only Apluda mutica), and circular/round (only Themeda arundinacea) in very low to negligible frequencies. Short saddle, plateau saddle, collapsed saddle, four horned rondel, spool/ horned tower, wavy top rondel, crescent moon, complex tower, biconvex, and bulliform morphotypes were completely absent. Polylobate phytolith diversity The detailed variability of polylobate phytoliths was
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documented and considering the number (from trilobate to nonalobate), regularity (regular or irregular), and diameter of the lobes (small, medium or large), 27 subtypes of polylobate (table 3) were isolated from
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compositus is completely devoid of the above mentioned polylobate subtypes. Furthermore, exclusive occurrence of octa-regular-small, octa-irregular-small, nona-regular-small, and nona-irregular-small subtypes in Themeda arundinacea facilitate in its differentiation from Apluda mutica. We have also employed statistical analysis to find out affinities between polylobate subtypes and very high polylobate producing grass taxa. Correspondence
Fig. 1: Box and whisker plot (mean/mean±SE/mean/±SD) of isolated principal phytolith morphotypes (by Statistica 10) showing dominance of polylobates over all other morphotypes in the reported three grasses
these 3 taxa. Among the 3 taxa, Oplismenus compositus (tribe – Paniceae, subtribe – Boivinellinae) produce up to penta-lobate (consist of 5 lobes) types. Apluda mutica (tribe - Andropogoneae, subtribe Ischaeminae) and Themeda arundinacea (tribe Andropogoneae, subtribe - Anthistiriinae) yielded polylobates with more than five lobes (6-9 lobes) but only Themeda arundinacea produced polylobates with 8-9 lobes. Tri-regular-small subtype was found to be most frequent (highest 19.72 % in Oplismenus compositus) followed by tri-regular-medium, tetraregular-small, hexa-regular-small, penta-irregularsmall, tetra-irregular-small, and tetra-regular-medium. Taxonomic and ecological significance These three taxa (49-55% polylobate frequency) can easily be differentiated from all other grasses (0-33 %) of the region by their relatively very high polylobate production. Proposed micro-morphological classification of polybates can be applied to further distinguish these three panicoid grasses. Hexa-regular-small, Hexa-regular-medium, Hexa-irregular-small, Heptaregular small, and Hepta-irregular-small subtypes were isolated in significant amount in both the grasses under tribe –Andropogoneae i. e. Apluda mutica and Themeda arundinacea. The only very high polylobate yielding grass under tribe Paniceae, Oplismenus
Fig. 2 : Selected polylobate sub-morphotypes retrieved from the three grasses. Light microscopic images (1-12) and scanning electron microscopic images (13-20). (Tri-regular-small - 1. Oplismenus compositus), (Tri-regular-medium - 2. Themeda arundinacea), (Tri-regular-large - 3. Apluda mutica, 13. – O.compositus), (Tetra-regular-medium – O. compositus), (Tetrairregular-medium 4. O. compositus, 14. A. mutica), (Penta-regular-medium 16. O. compositus), (Penta-irregular-medium –5. – A. mutica, 6. – T. arundinacea), (Hexa- regular –medium – 12. A. mutica), (Hexa-irregular-small 9. - T. arundinacea, 17. – A. mutica 19. T. arundinacea), (Hepta-irregular small– 10. T.arundinacea), Octa-regular-small 11.- T. arundinacea), (Octa-irregular-small – 7. – T. arundinacea, 8. – T. arundinacea, 18. – T. arundinacea), (Nona-irregular-small, 20. T.a arundinacea)
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Table 1: Three Panicoid grasses along with their collection areas, habitats, and principal phytolith assemblages Grass Taxa
Tribes
Collection areas
Habitat/Distribution
and coordinates
Principal Phytolith morphotypes a
Oplismenus
Paniceae
compositus
Canning
A mesophytic grass
Bl, Pl, Cr, Ls,
22°17'29.77"N
usually shade loving
Two hr, Three
88°40'40.81"E
growing in hedges or
hr, Py ron, El
near the village path.
ron, K ron, Trapez, Elo
Apluda mutica
Andropogoneae
Sonarpur
Often growing into
Bl, Pl, Cr, F tw,
22°26'6.05"N
small bushy
El ron, K ron, O
88°24
undergrowth, often
ron, Trapez, Elo
'51.12"E
found in hedges and among bushes, also along forest margins and irrigation ditches. Themeda
arundinacea
Andropogoneae
Baruipur
Common along
Bl, Pl, Cr, Two
22°21'33.24"N
margins of forests,
hr, El ron, K
8 8°25'48.69"E
banks of streams,
ron, Trapez, Cir,
usually in cool and
Elo, Oth
damp situations. a
Abbreviations used for phytolith morphotypes: Bl = Bilobate, Pl = Polylobate, Cr = Cross, Ps = Plateau saddle, Ls = Long saddle, F tw = Flat tower, Ov ron =Oval rondel, Two hr = Two horned rondel, Three hr = Three horned rondel, Py ron = Pyramidal rondel, El ron = Ellipsoid rondel, K ron = Keeled rondel, Trapez = Trapeziform, Cir = Circular, Elo = Elongate, Oth = Others)
analysis (CA) is well established to find out taxonomic resolution of phytolith spectra. (Barboni and Bremond, 2009; Rossouw, 2009; Neumann et al., 2016). In the CA ordination diagram of dimension 1 and 2 (Fig. 3), polylobate sub-morphotypes were closely associated with specific grass species exhibiting linkages with that grass taxa. Tri-regular-small, tri-regular-medium, triregular-large, tetra-regular-large, tri-irregular-medium, tetra-irregular-medium subtypes were found to be associated most closely with Oplismenus compositus. Apluda mutica displayed strong relationship with tetrairregular-small, penta-irregular-medium, penta-regularlarge, tetra-irregular-medium, hexa-regular-medium,
penta-irregular-small, hexa-irregular-small, hexa-regular-small, and hepta-regular-small subtypes whereas Themeda arundinacea showed firm correspondence with tri-irregular-small, tetra-regular-small, tetra-regular-medium, hepta-irregular-small, octa-regular- small, octa-irregular- small, nona-regular- small, and nonairregular- small sub-morphotypes. All these three panicoid grasses have almost similar kind of ecological adaptations. They all are mesophytic grasses and mostly adapted to moist and damp places. They prefer to grow under shady places also. Since no other grasses of the region produce polylobates in
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Table 2: Sub-morphotypes of polylobate phytolith isolated from the 3 grasses
Sub-morphotypes
Size of phytolith/ lobe diameter (µm)
Sub-morphotypes
Size of phytolith/ lobe diameter (µm)
Tri-regular-small Tri-regular-medium Tri-regular-large Tri-irregular-small Tri-irregular-medium Tri-irregular-large
15-30/10 15-30/10
Penta-irregular-small Penta-irregular-medium Penta-irregular-large Hexa-regular-small Hexa-regular-medium Hexa-irregular-small
20-40/10 25-45/
