Published under the author's permission

STRUCTURAL CHARACTERISTICS

OF VESSEL ELEMENTS IN STEMS

OF SOME MANGROVES



MONORANJAN GHOSE AND SAUREN DAS
Agricultural Science Unit, Indian Statistical Institute,
203, B. T. Road, Calcutta-700 035, India.


ABSTRACT

  The occurrence and types of perforation plates, end wall slopes, vessel frequency, length to width ratio and specialization index with respect to end wall characteristics of vessel elements in stems of 21 species of ten families of mangroves of Sundarbans (West Bengal) are described. Plants were collected from two different ecological habitats, slope (frequent tidal influence), and ridge (occasional tidal influence). The vessel elements of the plants growing on slope have smaller dimensions, but more or less similar length :width ratios and specialization indices in comparison to those of the ridge region. The width of vessel elements is significantly low and the frequency of vessels per unit cross sectional area is considerably high in slope-plants than ridge-plants. The vessel elements of the species of Rhizophoraceae and Palmae show scalariform perforation plates, and others show simple ones.

KEY WORDS : ecology, habitat, mangroves, vessel elements

INTRODUCTION

  Mangroves are the heterogeneous assemblage of halophytic woody plants which grow in littoral zones of tropicals. Most of the tree and shrub representatives are adapted to the saline habitat in various ways by the presence-of stilt roots, succulent leaves with thick cuticle, sunken stomata, pneumatophores and viviparous germination of seeds. Equable temperature, high humidity, high saline condition of water and soil, and varied precipitation are the common ecological factors of a mangrove vegetation. Wood anatomical stuidies of fossil and living mangroves of Sundarban Botanical Contactor (West Bengal, India) were carried out for comparision and identification of burried woods in order to comment on the history of vegetation of the lower Bengal basin by Chanda and Mukherjee (1969), and Mukherjee (1969). Their work was mainly confined to gross anatomy of woods rather than the tracheary elements.

  Moll and Janssonius (1914) compared vessel density in wood of Philippine-mangroves and non-mangrove species. They observed that the number of vessels per unit cross sectional area in mangrove wood was much greater than that of nonmangrove wood. This was further confirmed by Panshin (1932). Janssonius (1950) also reported that the diameter of individuel vessels of mangrove wood was considerably narrow. He found a correlation between the number of vessels and the frequency of inundation. The more frequent the area was inundated in which the species grew, the larger was the number of vessels per unit cross sectional area of wood. Carlquist (1975) considered scalariform perforation plates as functionally disadvantageous as compared to simple perforation plates, because of resistance to water flow. According to Cheadle (1 943), a vessel element is termedprimitive when it has oblique end walls with perforation plates that has many closely spaced bars, and advanced when it has slightly oblique to transverse end walls with simple perforation plates and of shorter length. Aldridge (1978) hypothesized that length to width ratio of vessel elements also indicates the degree of specialization of vessel elements, which she proved in studying evolution within a nonmangrove genus Sonchus. A high ratio indicates primitiveness and low ratio, advancement.

  Mangrove vegetation of Sundarbans is probably the largest of all such formation in the world, covering about 4200 km' area, formedjointly by the two rivers, the Ganges and Brahmaputra (Banerjee 1964). Sundarbans is composed of innumerable islands. Each island is crisscrossed by a number of canals of different size forming a network, and each mesh encircles a land mass. Such a land mass is subjected to differential tidal influence. The centre receives less tidal influence than the edge (Mukherjee, Mukherjee 1978). Some species of mangroves prefer frequent tidal influence (slope) and others prefer limited tidal influence (ridge). It is probable that the tracheary elements of these two categories of mangroves may show some differences in their dimensions, density and structure. The objectives of this paper are to provide basic information on dimension, perforation plates, end wall slopes, density and types of vessel elements, and to determine the degree to which these characteristics of vessel elements differ in the plants of slope and ridge.

MATERIALS AND METHODS

  Small pieces of mature stem were studied in 21 species of mangroves from Sundarbans of West Bengal, India (Table 1). The nomenclature followed here is that of Tomlinson (1986). Most of the investigated taxa were trees and shrubs except one woody herb, Acanthus ilicifolius. Only two monocotyledons - Phoenix paludosa and Nypa fruticans (Palmae) were available in the study-area. The samples were collected from two different zones: (i) slope (usually 0.0 m = < 5.0 m), the area which remains submergea during high tide and are inundated twice a day; and (ii) ridge (usually 5.0 m-8.0 m), the area that receives tidal water twice daily for two days in a month during spring tide and occasionally during storms and cyclones. Small pieces of stems were fixed in FAA for 48 h and then boiled in 1 0% caustic potash for 10-15 minutes and washed thoroughly. Then the materials were soaked in 25% chromic acid for 15-20 minutes, and again washed in water. The mascerated materials were teased apart and mounted on a slide in phenol-glycerine. Length, width, end wall-slopes and the types of perforation plates of vessels were recorded. The statistical test was employed after Steel and Torrie (1960). Categories of perforation plates and end wall slopes : The terminology for perforation plates (except mixed which is taken from Ghose 1984) was used after Esau (1958). The different vessel elements were categorized as follows : (i) both perforation plates simple (Fig 1 A-F, K-N, S-U, 2B-D), (ii) both perforation plates scalariform (Fig 1 G-J, Q-R; 2A,E,FH), and (iii) mixed type, i e one perforation plate

Elements of vessel

Figure 1 A-U. Vessel elements.

A. Acanthus ilicifolius. B. Aegialitis rotundifolia. C. Aegiceras corniculatum. D. Avicennia alba.
E. Avicennia marina. F. Avicennia officinalis. G. Bruguiera cylindrica. H. Bruguiera gymnorrhiza.
I. Ceriops decandra. J. Ceriops tagal. K. Excoecaria agallocha. L. Heritiera fomes.
M. Heritiera littoralis. N. Kandelia candel. O. Nypa fructicans. P. Phoenix paludosa.
Q. Rhizophora apiculata. R. Rhizophora mucronata. S. Sonneratia apetala.
T. Xylocarpus granatum. U. Xylocarpus mekongensis.

Fig 2A-H Vessel elements. Fig 2A-H
A. Nypa fruiticans.
B. Xylocarpus mekongensis.
C. Argialitis rotundifolia.
D. Bruguiera gymnorrhiza.
E. Avicennia marina.
F. Phoenix paludosa.
G. Rhizophora apiculata.
H. Ceriops tagal.


is different from that of the other of the same vessel element (Fig 1 0). Regarding the end wall slopes, Cheadle's (1 943) and Ghose's (1 984) classifications were followed: (i) both the end walls transverse (Fig IC, F, S; 2B, D). (ii) both the end walls oblique (Fig IB, H-J, M, 0-R, U; 2A, E-H), and (iii) mixed type (Fig 1 A, D, E, G, K, N, T; 2C) i e one end wall transverse and the other oblique.

In order to ascertain whether the vessel elements are advanced or primitive in light of ecological consideration, both length:width ratio and specialization index were employed. A combined specialization index for both end wall slopes and perforation plates was formulated for each species using the a modified formula of Ghose (1984) and Klotz (1978).

Specialization index X 100

= 1 (% of both perforation plates simple + % of both end walls slopes transverse) +2(% of mixed perforation plates + % of mixed end wall slopes) +3(% of both perforation plates scalariform + % of both end wall slopes oblique).

A high index value indicates primitive vessel elements and a low one, more advanced. Nypafruticans and Phoenixpaludosa being the only two members of monocotyledons,, were not subjected to statistical test, instead their mean values were considered.

RESULTS

Types of vessel elements : The end wall characters of vessel elements are given in table 1. The vessel elements of most of the studied mangroves have simple perforation plates (Fig 1). Scalariform perforation plates are dominant in the members of the family Rhizophoraceae with the exception of K candel, which has simple perforation plates. Scalariform perforation plates also occur in Nfruticans and P paludosa. Mixed type perforation plates occur, though in small percentages, in B cylindrica, Nfruticans and Ppaludosa. End wall slopes of vessel elements show a wide range of variations such as, both end walls transverse, both end walls oblique and mixed type. Exclusively transverse slopes occur in Agiceras corniculatum and oblique in Bruguiera gymnorrhiza, Rhizophora mucronata and Phoenix paludosa. It is interesting to note that some species with 100% simple perfortion plates (advanced character) possess higher percentage of both oblique (primitive character) end walls, e.g. E agallocha (60%), K candel (73%), H fomes (47%) and H littorales (40%).

The lateral wali pitting of vessel elements in mangroves is basically oftwo types : alternate and scalariform (Fig 1) Alternate wall pitting is more common and found in 12 species (e g Acanthus, Aegiceras, Avicennia) and scalariform type in nine species (e g Bruguiera, Ceriops, Rhizophora, Nypa, Phoenix). Scalariform pitting occurs in all the members of the family Rhizophoraceae except K candel, which shows alternate pitting (Fig 1, 2). Long tails or ligules at the end walls of vessel elements occur in B gymnorrhiza, C decandra, C tagal and K candel (Fig IH-J; 2A, H), Nfruticans. Ligules are absent in Acanthus, Aegialitis, Aegiceras and Phoenix, while they are very small or absent in the other species.

Dimension and frequency of vessel elements : The dimensions, frequencies, specialization indices and rato of length to width of vessel elements are provided for slope and ridge species in table 2. The average of mean length of vessel elements in the slop (0.362 mm) is lower than the ridge (0.431 mm) species. The mean length of vessel elements in monocotyledons is relatively high with respect to dicotylendons. However, the difference in mean length of vessel elements between these two habitats is statistically not significant.

DISCUSSION

The present investigation shows that diameter of vessel elements of mangroves ranges from 0.038 - 0.099 mm. Janssonius (1950) and Panshin (1932), while working on Javan and Philippine mangroves, also recorded the diameter of vessel to range between 0. 1 and 0. 15 mm.

The average width of vessel elements of slope-plants is significantly

Table 1. End walls of vessel elements is mangroves
  Nature of Perforation plate (%) Nature of
end		 wall slope (%)
Taxa Habit BS Mixed BSp BO M BT
Dycotyledons
Acanthus ilicifolius L
Avicenniaceae		 Herb - - 100 7 40 53
Avicennia alba
Blume
Avicenniaceae		 Tree - - 100 13 20 67
A marina (Forsk)
Vierh
Avicenniaceae		 Tree - - 100 - 27 73
A officinalis L
Avicenniaceae		 Tree - - 100 7 13 80
Excoecaria agallocha L
Euphorbiaceae		 Tree - - 100 60 27 13
Xylocarpus granatum
Koing
Meliaceae		 Tree - - 100 - 40 60
X mekongensis Pierre
Meliaceae
 Tree - - 100 27 13 60
Aegiceras corniculatum
(L) Myrsinaceae		 Shrub - - 100 - - 100
Aegialitis rotundifolia
Roxb
Plumbaginaceae		 Shrub - - 100 33 20 47
Bruguiera cylindrica
(L)BI
Rhizophoraceae		 Tree 93 7 - 73 27 -
B gymnorrhiza
(L) Lamk
Rhizophoraceae		 Tree 100 - - 100 - -
Ceriops decandra
(G) D H
Rhizophoraceae		 Shrub 100 - - 87 13 -
Ceriops tagal
(Pierr) Rob
Rhizophoraceae		 Tree 100 - - 60 40 -
Kandelia candel
(L) Druce
Rhizophoraceae		 Tree - - 100 73 27 -
Rhizophora apiculata
BI
Rhizophoraceae		 Tree 100 - - 73 27 -
R mucronata
Lamk
Rhizophoraceae		 Tree - 100 - - 100 -
Sanneratia apelata
Buch Ham
Sonneratiaceae		 Tree - - 100 27 20 53
Heritiera fomes
Buch Ham
Sterculiaceae		 Tree - - 100 47 - 53
H littoralis
Dryland
Sterculiaceae		 Tree - - 100 40 13 47
Monocotyledons
Nypa fructicans
(Thunb) Wurmb
Arecaceae		 Tree 67 33 - 80 20 -
Phoenix paludosa
Roxb
Arecaceae		 Shrub 47 53 - 100 - -

Table 2. Dimensions of vessel elements is mangroves
Species vessel/mm² lenght(L) width(W) L/W SI
DICOTYLEDONS: SLOPE
A ilicifolius 68.3±1.8 0.271±0.006 0.042±0.001 6.73±0.400 2.54
A rotundifolia 61.68±1.08 0.133±0.003 0.047±0.001 9.82±0.173 2.86
A corniculatum 269.85±1.18 0.228±0.006 0.46±0.001 4.95±0.343 2.43
A marina 42.96±2.57 0.277±0.010 0.054±0.001 5.12±0.210 2.28
A officinalis 37.45±2.43 0.240±0.004 0.075±0.002 3.20±0.182 2.28
B officinalis 37.45±2.43 0.240±0.004 0.075±0.002 3.20±0.182 2.28
B cylindrica 69.72±2.64 0.431±0.006 0.055±0.001 7.83±0.268 5.66
B gymnorrhiza 74.90±3.60 0.698±0.019 0.055±0.028 10.41±0.721 6.00
K candel 123.36±3.60 0.460±0.008 0.040±0.009 12.40±0.343 3.74
R apiculata 39.21±2.79 0.345±0.003 0.055±0.001 6.17±0.192 5.74
R mucronata 45.16±2.84 0.407±0.004 0.038±0.001 10.71±0.383 6.00
S apelata 57.27±2.74 0.454±0.017 0.076±0.002 5.69±0.040 2.74
Average 80.90±20.247 0.362±0.047 0.053±0.004 7.55±0.877 3.8
DICOTYLEDONS: RIDGE
A alba 39.65±2.64 0.276±0.009 0.059±0.002 4.67±0.320 2.46
C decandra 89.21±3.83 0.743±0.013 0.065±0.001 11.43±0.421 5.88
C tagal 77.10±2.23 0.683±0.019 0.039±0.001 17.66±0.910 5.60
E agallocha 31.94±1.98 0.587±0.019 0.078±0.002 7.52±0.273 3.48
H fomes 39.65±2.43 0.266±0.004 0.070±0.002 3.80±0.134 2.94
H littoralis 32.11±2.19 0.299±0.004 0.059±0.001 5.06±0.152 2.94
X granatum 37.45±1.79 0.289±0.005 0.099±0.002 2.91±0.113 2.40
X mekongensis 39.65±2.94 0.307±0.008 0.074±0.001 4.14±0.173 2.68
Average 48.35±7.763 0.431±0.072 0.068±0.006 7.15±1.781 3.5
"t" value 1.32 0.841 2.159* 0.219 0.351
MONOCOTYLEDONS: SLOPE
N fratuicans 61.62±2.83 0.627±0.017 0.067±0.002 9.35±0.059 5.48
MONOCOTYLEDONS: RIDGE
P paludosa 71.24±2.43 1.955±0.031 0.060±0.001 33.25±1.291 5.48


lower than that of the ridge-plants. Considerable decrease is also noticed in respect to length of vessel elements. On the contrary, density of vessels is considerably greaterer in the slope-plants than those of the ridge. Janssonius (1950), on the basis of some observations on three different species of Bruguiera at different ecological zones in Java, found a correlation between the number of vessels and frequency of inondation by the tidal water. He concluded that the more frequent the area is inundated in which the species grows, the larger the number of vessels per unit sectional area of wood. The present observation is in conformity with his view. Similar results were also obtained by Aldridge (1 978) and Carlquist (1966) in non-mangrove genus Sonchus, where they observed marked decrease in vessel length and breadth from xerophytic to coastal species. Why the vessel elements of the slope plants are or should be narrower than those of the ridge plants? Scholander et al (1964, 1965) measured high tensions (negative pressure) in xylem and observed high density of narrow vessels in stems of mangroves. Frequent high tension in xylem increases the likelihood of cavitation within vessels during stressful conditions, which is directly dependent on vessel diameter (Zimmermann 1983). Hence, the narrowness of vessels in mangrove-woods is for safety since it reduces the loss of conducting units by embolism (Tomlinson 1986). As the roots of the slope plants are inundated more frequently by the saline tidal water than those of the ridge plants, the former group has to maintain larger number of narrow vessels overcoming cavitation problem.

Carlquist (1966) reported that vessel elements having a few or no bars on their perforation plates represent a more favourable adaptation to dry environmental conditions than do perforation plates with numerous and closely spaced bars. To some extent, palms also display this correlation between form of perforation plates and degree of moisture demand in the environment (Klotz 1978). The vessel elements of mangrove woods have simple perforation plates except in most members of Rhizophoraceae, which have scalariform perforation plates. Kandelia candel, the only species of the family Rhizophoraceae, possesses simple perforation plates. The end wall slope of the vessel elements in Rhizophoraceae also shows higher obliqueness. Scalariform perforation plates distinguish the mangrove Rhizophoraceae from their terrestrial relatives (van Vliet 1976). According to Tomlinson (1986) Rhizophoreae is monophyletic and evolved from an ancestor that had scalariform perforation plates in its wood. Scalariform perforations were retained in descendants because they are adaptively neutral.

The average specialization index does not show any difference between the two habitats. But individuel figures vary widely among members of different families. This indicates that the end wall characteristics of vessel elements are rigid hereditary characters, while density and diameter are influenced the most by environmental fluctuations.


ACKNOWLEDGEMENT

We thank Dr B C Sasmal, Jute and Allied Fiber Crop Research Institute, Barrackpore, for his help in statistical analysis.

References
Aldridge A E 1978 Bot J Lin Soc 76 249
Banerjee A K 1964 In Cent Comm Vol, West Bengal Forests, Calcutta, 166
Carlquist S 1966 Aliso 6 25
Carlquiest S 1975 Ecological strategies of xylem evolution. Univ California Press, U S A
Chaedle V 1 1943 Am J Bot, 30 484
Chanda S, Mukherjee B B 1969 Sci Cult 35
Esau K 1958 Plant anatomy, John Wiley New York
Ghose M 1984 Principes 28 179
Janssonius H H 1950 Blumea 6 465
Klotz L H 1978 J Arnold Arbor, 59 105
Moll J W, Janssonius H H 1914 Leiden E J Brill 3 1
Mukherjee B B 1969 Trans Bose Res Inst 32 59
Mukherjee B B, Mukherjee J 1978 Phytomorphology 28 175
Panshin A J 1932 Phlipp J Sci 48 143
Scholoander P F, Hamme] H T, Hemmingsen E A, Bradstreet E D 1964 Proc Nat Acad Sci (U S A) 52 119
Scholander P F, Hammel H T, Bradstreet E D, Hemmingsen E A 1965 Science 148 339
Steel R G D, Torrie J H 1960 Principles and procedures of statistics. McGrawhill, New York
Tomlinson P B 1986 'Me Botany of Mangroves, Cambridge Univ Press, New York van Vliet G J C M 1976 Leiden Bot Ser 3 20
Zimmermann M H 1983 Xylem structure and the ascent of sap. Soringer Verlag, Berlin

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