RESEARCH COMMUNICATIONS
Pollination biology in Bombax ceiba
Linn.
Ashoke Bhattacharya and Sudhendu Mandal*
Department of Botany, Visva-Bharati University,
Santiniketan 731 235, India
A study of flower morphology, anthesis, pollen production, foraging nature of flower visitors, in vitro
pollen germination and stigma receptivity of Bombax
ceiba Linn. of the family Bombacaceae has been
made. The flowers are large with numerous stamens
which open in post middle night and continue up to
the morning. Anther dehisced after flower opening.
During daytime, different types of birds visit the
flowers and subsequently help in pollen dispersal
and pollination when stigmas remain receptive. Each
flower produced 8,863,000 pollen grains which are of
3-colporate, with reticulate ornamentation and thick
exine. In vitro pollen germination study indicated
that best germination (97%) along with 2940 µm
tube development, takes place in 20% sucrose combined with 500 µg/ml H 3BO 3 solution. Among different salts of Ca, Mg and K, only Ca(NO3)2⋅ 4H2O
showed significant result with 54% germinating pollen along with 420 µm tube length in 50 µg/ml
Ca(NO3)2⋅ 4H2O solution. Maximum stigma receptivity was noticed during the first day after anthesis
with 61% in vivo germinating pollen captured with
unicellular pointed papillae cells over receptive
stigma surface. Atmospheric pollen frequency was
found to be 5.17% in 10.00 h. No fruit setting was
observed in netted and bagged flowers, which
strongly indicates that some external agents are required for successful pollination.
T HE mechanism of pollination among the higher plant
groups has been under investigation from very early
times and it is highly significant in biological studies. It
is particularly important among other aspects of biological studies in ecology, co-evolution, variation and
speciation, classical and applied genetics and plant
breeding. The knowledge of pollination biology is a
prerequisite in plant breeding and for obtaining better
yields of crops. Variability is controlled by the breeding
system, of which pollination mechanism forms an integral component1. Pollination biology has shown a new
phase of synthesis and correlation. During its entire
flowering period, a plant species needs several flower
visitors for its pollination. In the same way, the flower
visitors require a number of plant species to provide
them continuous nourishment. Baker2 considered the
pollination relationships on a community basis. Plant–
pollinator interactions are crucial in determining community structure and its functioning3,4. Pollen produc*For correspondence. (e-mail: [email protected])
1706
tivity of a plant species indicates the biological efficiency of a particular plant. Pollination biology of some
angiospermic plants has been studied1–17. But an adequate knowledge about the pollination biology of Bombax ceiba is lacking since the plant is economically
important on account of the presence of floss surrounding the seeds, which is used for making pillows, cushions, etc.
It is well known that successful fruit and seed setting
depends largely on viable pollen grains. Viability could
be measured by in vitro pollen germination techniques.
Many organic and inorganic substances like sucrose,
H3BO3, Ca(NO3)2⋅4H2O, KNO3 and MgSO4⋅7H2O exert
an effect on in vitro pollen germination. Despite this, in
vivo pollen germination could be helpful in determining
stigma receptivity at different times after anthesis.
The principal objective of the present investigation is
to acquire detailed knowledge about the floral biology,
pollen dispersal, pollen–pollinator interaction, pollination mechanism, effect of different organic and inorganic nutrients on in vitro pollen germination, stigma
morphology and receptivity of B. ceiba Linn. of the
family Bombacaceae.
An extensive field exploration has been done in the
University campus with a view to finding out the flowering period and floral nature of the selected plant.
Flower colour, odour and nectar were observed visually.
Anthesis and anther dehiscence were observed using a
fluorescent lamp at night and a hand lens, following the
method of Reddi and Janaki Bai18 and Mathur and
Mohan Ram9. Pollen productivity was estimated according to the method of Mandal and Chanda19. Pollen morphology was studied using light microscope and
scanning electron microscope following acetolysis
method20. Scanning electron microscopic pictures were
taken from RSIC, Bose Institute, Calcutta. Atmospheric
pollen frequency was measured with the help of ‘Rotorod sampler’ designed by Perkins21. Contribution of
flower visitors to fruit setting was determined by netting
and bagging of unopened flowers, randomly selecting
ten plants in different locations. To have a knowledge
about in vitro pollen germination, sucrose solution of
different concentrations (1–40%), calcium nitrate (25–
500 µg/ml), boric acid (50 –1200 µg/ml), potassium nitrate (50–500 µg/ml) and magnesium sulphate (50–
500 µg/ml) were prepared. One drop (50 µl) of each
solution was poured, both individually and combined,
on groove slides separately. Freshly collected, uncontaminated pollen from immediately dehisced anther was
put onto the solution. The slides were kept within petri
dishes lined with moist filter paper. After the stipulated
period, the percentage of pollen germination and pollen
tube elongation was noticed under microscope and calculations were made following the method of Shivanna
and Rangaswamy22. Receptivity of stigmas at different
times of flower opening was measured following in vivo
CURRENT SCIENCE, VOL. 79, NO. 12, 25 DECEMBER 2000
RESEARCH COMMUNICATIONS
pollen germination according to the standard method
suggested by Joshi Rao and Saoji23. For scanning electron microscopic analysis, the receptive stigmas were
fixed in 2% glutaraldehyde17 and after washing in phosphate buffer (pH 7.2), these were dehydrated in ethanol
series (30–90%), critical point-dried and photomicrographs were taken in P-SEM-500 at low voltage. Identification of the flower visitors was obtained from the
Zoological Survey of India, Calcutta.
B. ceiba Linn. belonging to the family Bombacaceae
is a large, deciduous tree growing wild on the roadsides
of Santiniketan campus. It flowers from January to
March. The trunk and branches are covered with stout,
hard, conical prickles when young, provided with welldeveloped buttresses; branches are whorled, leaves are
digitate with 5–7 ovate, elliptic-lanceolate or obovate,
glabrous 10–18 cm long leaflets; in the leaf, the petioles
are longer than the leaflets.
The flowers are large, numerous, fascicled near
branch-ends, ebracteate, actinomorphic, crimson; the
calyx is leathery, cup-shaped and persistent; the petals
are fleshy; the stamens are numerous, forming 5bundles; the level of the stigma is higher than the level
of the anthers, the stigma is digitate. Being ornithophilous, the flowers are adapted by the presence of hard
flower-wall, stiff filaments, well-protected ovary, abundant nectar, good capillary system bringing nectar up or
preventing its flowing out of a deep tube or spir and
absence of odour. Flowers usually appear when the trees
are leafless, before production of leaves.
Flowers start opening after midnight and remain till
the morning. The anther dehiscence takes place after
opening of flowers (Table 1). During daytime, many
flower visitors (Table 2) like Sturnus, Nectarinia, Acridotheres, Pycnonotus, etc. were observed, visiting the
flowers to feed on the nectar (Figure 1 a and b). They
help the flowers in pollination by their rapid and frequent visits to the flowers for nectar collection. The
birds land on the branches and try to push their beaks
into the flowers for collecting nectar and stored water
within the cup-shaped calyx. In this process, pollen
grains adhere to their rough beak surface. The pollen
grains are subsequently transferred to another flower of
same plant or another plant showing geitonogamy or
allogamy.
It has been observed that a good number of pollen
(8,863,000 pollen grains/flower) is produced, showing
5.17% atmospheric pollen frequency at 10.00 h (Table
1). Pollen grains are 3-colporate, euoblate, P/E
± 38.8 × 71.75 µm, polar outline triangular, polar view
± 64.7 µm across, equator ial outline elliptic, colpi narrowly elliptic, ± 25.65 µm long. ± 5.2 µm wide, sides
tapering towards pole, margin thick, exine ± 3.2 µm
thick, reticulate (Figure 2).
Studies on pollen viability through in vitro pollen
germination using different organic and inorganic nutriCURRENT SCIENCE, VOL. 79, NO. 12, 25 DECEMBER 2000
ents like sucrose, H3BO3, Ca(NO3)2⋅4H2O, KNO3 and
MgSO4⋅7H2O confirmed that pollen grains remain viable up to their transfer on stigma surface during the
receptive period. Effect of sucrose on in vitro pollen
germination study reveals that 71% germinating pollen
along with 237 µm tube development may occur in 20%
sucrose solution. Germinating potential was found to be
less in low (2–15%) as well as very high (25–40%) concentrated sucrose solution (Table 3). Among different
salts of B, Ca, K and Mg, only B and Ca exert an effect
on in vitro pollen germination of selected plants. It has
been observed that 51% pollen germination along with
945 µm tube elongation occurs in 300 µg/ml H 3BO3
solution. Germinating percentages were significantly
low in low or high concentration H3BO3 solutions
(Table 4). Apart from this, 54% pollen germination and
420 µm tube elongation were found in 50 µg/ml
Ca(NO3)2⋅4H2O solution. Germinating potential is very
low in other solutions of Ca(NO3)2 (Table 5). No germinating pollen grains were found in KNO3 and
MgSO4⋅7H2O solutions. Best pollen germination (97%)
along with 2940 µm tube length (Figure 3) was noticed
in 20% sucrose supplemented with 500 µg/ml H 3BO3
Table 1. Floral characters of Bombax ceiba
Floral character
Observation
Flowering period
Flower type
Flower colour
Odour
Nectar
Flower opening time
Anther dehiscence time
Anther dehiscence mode
Number of anthers
Average number of pollens per anther
Average number of pollens per flower
Pollen type
Pollen shape
Pollen size
Atmospheric pollen frequency
Stigma type
Fruit setting (%) in open flowers
Fruit setting (%) in netted flowers
Fruit setting (%) in bagged flowers
January–March
Somewhat ornithophilous
Crimson
Absent
Present
Post midnight to morning
After anthesis
Longitudinal
Many (100 approx.)
88,630
88,63,000
3-colporate
Euoblate
± 38.8 × 71.75 µm
5.17% in 10.00 h
Above anther level, digitate
with stout style and wet type
24
Nil
Nil
Table 2. List of flower visitors of Bombax ceiba
Visitor
Acridotheres sp.
Dumetia hyperythra
Macronous gularis
Nectarinia sp.
Pycnonotus cafer
Sturnus contra
Order/Family
Strunidae
Musicapidae
Musicapidae
Nectariniidae
Pycnonotidae
Sturnidae
Visiting time
Foraging nature
Day
Day
Day
Day
Day
Day
Nectar
Nectar
Nectar
Nectar
Nectar
Nectar
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RESEARCH COMMUNICATIONS
solution; but germinating percentages were gradually
low with lower and higher concentrations of the
substrate (Table 6). Combinations of different concentrated media did not show any improvement in germination.
Over the wet type receptive stigma head, there are
numerous prolonged, rectangular, thin-walled papillae
cells arranged loosely-forming intercellular spaces. In
the median portion of stigma tissue, cells are larger with
moderate spaces. Stigma tissue organization becomes
narrow towards end. The surface is impregnated with a
uniform layer of large, triangular, pointed, broadlyspaced papillate cells which are involved in pollen capture (Figures 4 and 5).
Stigmas were more receptive, i.e. 70% on the first day
after anthesis, showing 61% in vivo germinating pollen
along with 317 µm long pollen tubes on the stigmatic
surface (Figure 6), but the receptivity percentages and
in vivo germinating pollen percentages decrease in successive days after anthesis (Table 7).
Study of anthesis and anther dehiscence is vital for
subsequent dispersal of pollen grains into the atmosphere24. Birds, with rough-surfaced beaks, are good pollinators25. The efficiency of nectar uptake may vary
among different bird species depending upon the adaptive features of bird flowers. From the point of view of
pollination, it can be stated that birds visit flowers either for collecting nectar or chasing insects. A critical
observation on the flowers of B. ceiba suggests that the
birds visit these flowers only for collecting nectar and
stored water. The habit of nectar collection has arisen in
different groups of birds in different regions. Flowers
and their birds may have developed together with mutual influences25.
Pollen productivity has an impact on plants, animals
and human beings and it depends upon anther length,
pollen grain size and mode of anther dehiscence26,27.
Total pollen output is related to fruit and seed setting.
The presence of pollen in the atmosphere is not related to pollination of B. ceiba because no fruit setting
was observed in netted flowers. The pollen frequency in
air may vary from time to time, day to day, even season
to season and many biological as well as physical processes alter the releasing mechanism28. Productivity and
releasing mechanism of pollen grains of selected plants
are corroborated by other workers27,29–34.
Regarding the effect of sucrose on in vitro pollen
germination of B. ceiba, it is believed that pollen of B.
ceiba requires more respiratory substrates like sucrose
for its germination and also requires B and Ca for its
germination and tube extrusion; but may not need K and
Mg for the same. From the observation of in vitro pollen germination it can be concluded that the combined
effect of concentrated sucrose and H3BO3 plays a significant role in yielding best germination and tube elongation. The reason behind utilization of highly concen1708
Figure 1. Birds (a) Pycnonotus cafer and (b) Sturnus contra visiting
the flowers of B. ceiba.
Figure 2. Pollen grains showing surface and apertures (SEM
×1250).
CURRENT SCIENCE, VOL. 79, NO. 12, 25 DECEMBER 2000
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Table 3. Effect of sucrose on in vitro pollen germination of Bombax ceiba
After 4 h
Concentration
(%)
2
5.
8
10
12
15
20
25
30
40
Germination
(%)
–
–
2
14
26
42
65
59
16
–
Tube length
(µm)
After 8 h
Germination
(%)
–
–
87
135
142
171
225
146
92
–
–
5
5
18
31
48
67
62
16
8
After 12 h
Tube length
(µm)
–
91
94
144
158
179
235
152
94
91
Germination
(%)
–
5
5
18
36
48
71
62
20
8
Tube length
(µm)
–
94
97
144
198
234
237
152
94
91
Table 4. Effect of boric acid on in vitro pollen germination of Bombax ceiba
After 4 h
Concentration
(µg/ml)
100
200
300
400
500
600
700
800
900
1000
Germination
(%)
6
19
47
19
12
7
–
–
–
–
Tube length
(µm)
After 8 h
Germination
(%)
390
625
920
354
264
270
–
–
–
–
8
20
50
21
14
9
3
3
–
–
After 12 h
Tube length
(µm)
405
640
945
375
270
280
180
126
–
–
Germination
(%)
8
23
51
24
14
10
3
3
2
–
Tube length
(µm)
405
645
945
375
270
280
180
126
112
–
Table 5. Effect of calcium nitrate on in vitro pollen germination of Bombax ceiba
After 4 h
Concentration
(µg/ml)
25
50
100
200
300
500
Germination
(%)
27
46
–
–
–
–
Tube length
(µm)
After 8 h
Germination
(%)
270
392
–
–
–
–
29
51
10
10
4
–
trated sucrose and H3BO3 may be due to the presence of
low amounts of sugar and boron in the pollen of B.
ceiba. Sucrose is the best carbohydrate source for pollen
germination, having its function in maintaining osmotic
pressure of the medium and acting as a substrate for
pollen metabolism35,36. The optimum concentration of
sucrose uptake varies from species to species. Boron is
a stimulatory agent for pollen germination and tube
elongation. It is involved with translocation and metabolism of sucrose. The formation of protrusions
through germ pores is independent of boric acid supply,
CURRENT SCIENCE, VOL. 79, NO. 12, 25 DECEMBER 2000
After 12 h
Tube length
(µm)
281
396
144
132
145
–
Germination
(%)
29
54
12
10
4
–
Tube length
(µm)
281
420
144
132
145
–
but tube growth depends upon the presence of boric
acid. The exact contribution of boron is still unknown,
but it is assumed that boron has an ability to make a
complex associated with sugar. Thus, the sugar–borate
complex has a better translocation ability than nonborate sugar molecules37 and it has a role in excessive
sugar polymerization. Regarding the effect of Ca on
pollen tube growth, it is said that calcium is concerned
with the crowding effect of pollen grains. The crowding
effect or population effect is found in the pollen of
many taxa36. Moderate germinating grains were ob1709
RESEARCH COMMUNICATIONS
Table 6. Effect of sucrose and boric acid on in vitro pollen germination of Bombax ceiba
After 4 h
Concentration
(% + µg/ml)
20
20
20
20
20
20
20
20
20
20
20
+
+
+
+
+
+
+
+
+
+
+
100
200
300
400
500
600
700
800
900
1000
1200
Germination
(%)
75
26
41
49
91
40
31
22
34
–
–
Tube length
(µm)
After 8 h
Germination
(%)
2582
616
2225
2297
2921
1870
960
624
610
–
–
81
28
42
51
95
42
32
24
36
16
–
After 12 h
Tube length
(µm)
Germination
(%)
2610
634
2264
2340
2936
1892
975
630
630
515
–
81
28
45
54
97
43
32
24
38
16
–
Tube length
(µm)
2620
634
2275
2349
2940
1892
975
670
630
535
–
Table 7. In vivo pollen germination of Bombax ceiba
Period after flower opening
Total number of stigmas observed
Number of stigmas showing germination
Percentage of stigma receptivity
Total number of pollen retained on the stigma
Mean number of germinated pollen
Percentage of germinated pollen
Mean tube length (µm)
First day
Second day
10
7
70
3540
2159.4
61
317
10
6
60
3810
1980.44
51.98
223
Third day Drooping stage
10
3
30
3950
1783
45.14
296
10
–
–
1892
–
–
–
Figure 3. In vitro germinating pollen grains showing pollen tubes
(LM ×100).
Figure 4. Papillae cells over stigma (SEM ×200).
served in larger population. According to Brewbaker
and Mazumder38, this population effect is due to a heatstable substance called pollen growth factor (PGF) and
it was found to be calcium ion39. As the salts of K and
Mg did not show any germinating pollen, it is predicted
that endogenous K and Mg of the pollen of B. ceiba is
sufficient for its requirement. Thus, the present observations on pollen germination are in conformity with those
of other workers40–47.
Receptivity of stigma is a critical factor for successful
completion of post-pollination events. Usually, it
becomes maximal soon after anthesis, but it varies
from species to species36. Pollen fertility and
pollen tube growth on the stigma surface and within
the style are very sensitive to temperature changes48.
After being successfully placed on the stigma
surface, the pollen undergoes hydration. After hydration, pollen wall proteins are released onto the stigmatic
surface49 and the stigmatic pellicle acts as a receptor of
pollen wall proteins23. Thus, the pollen grains are recognized and begin to germinate on the stigmatic surface.
1710
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Figure 5. Association of pollen grains with papillae cells (SEM
×400).
Figure 6. Pollen tube enters the stigma papillae cells (SEM ×800).
From the present preliminary observations on the pollination biology of B. ceiba, it can be concluded that
different bird species help in its successful pollination,
coinciding pollen viability and stigma receptivity.
1. Roy, R. P. and Choudhury, S. S., J. Indian Bot. Soc., 1981, 60,
21–23.
2. Baker, H. G., Science, 1963, 139, 877–883.
3. Heithaus, E. R., Ann. Missouri Bot. Gard., 1974, 61, 675–
691.
4. Frankie, G. W., in Tropical Trees: Variation, Breeding and
Conservation (eds Burley, J. and Styles, B. T.), Academic Press,
London, 1976, pp. 151–159.
5. Kapil, R. P. and Jain, K. L., Biology and Utilization of Insect
Pollinators for Crop Production, Haryana Agricultural University, Hissar, 1980.
6. Pant, D. D., Nantiyal, D. D. and Chaturvedi, S. K., Phytomorphology, 1982, 32, 302–313.
7. Subba Reddi, C. and Reddi, E. U. B., Proc. Indian Acad. Sci.,
1984, 93, 373–390.
8. Reddi, E. U. B. and Subba Reddi, C., Proc. Indian Natl. Sci.
Acad., 1985, 51, 468–482.
CURRENT SCIENCE, VOL. 79, NO. 12, 25 DECEMBER 2000
9. Mathur, G. and Mohan Ram, H. Y., Phytomorphology, 1986, 36,
79–100.
10. Pant, D. D. and Chaturvedi, S. K., Geophytology, 1986, 16, 119–
121.
11. Rama Devi, K., Atluri, J. B. and Subba Reddi, C., Proc. Indian
Acad. Sci. (Plant Sci.), 1989, 99, 223–239.
12. Solomon Raju, A. I. and Subba Reddi, C., Plant Species Biol.,
1989, 4, 157–167.
13. Jyothi, P. V., Atluri, J. B. and Subba Reddi, C., Proc. Indian
Acad. Sci., 1990, 100, 33–42.
14. Molau, U., Nord. J. Bot., 1993, 13, 149–157.
15. Johnson, S. D. and Steiner, K. E., Nord. J. Bot., 1994, 14, 481–
485.
16. Johnson, S. D., Nord. J. Bot., 1995, 15, 121–125.
17. Ciampolini, F., Faleri, C., Di Pietro, D. and Cresti, M., Ann.
Bot., 1996, 78, 759–764.
18. Reddi, C. S. and Janaki Bai, A., J. Bombay Nat. Hist. Soc., 1981,
77, 471–475.
19. Mandal, S. and Chanda, S., Biol. Mem., 1981, 6, 1–61.
20. Erdtman, G., Sven. Bot. Tidskr., 1960, 54, 261–264.
21. Perkins, W. A., Second Semi-Annual Report, Stanford Univ.,
1957, p. 66.
22. Shivanna, K. R. and Rangaswamy, N. S., Pollen Biology – A
Laboratory Manual, Narosa Publishing House, New Delhi,
1992.
23. Joshirao, J. A. and Saoji, A. A., J. Palynol., 1989, 25, 45–50.
24. Bhattacharya, K. N. and Datta, B. K., Grana, 1992, 31, 67–
71.
25. Faegri, K. and van der Pijl, L., The Principles of Pollination
Ecology, Pergamon Press, Oxford, 1980.
26. Linskens, H. F., in Sexual Plant Reproduction (eds Cresti, M.
and Tezzi, A.), Springer-Verlag, Berlin, 1992, pp. 203–218.
27. Reddi, C. S. and Reddi, N. S., Grana, 1986, 25, 55–61.
28. McCartney, H. A., Grana, 1994, 33, 76–80.
29. Vaish, R. S., J. Palynol., 1973, 9, 83–86.
30. Tilak, S. T., J. Palynol., 1987–88, 23–24, 101–116.
31. Agashe, S. N., in Recent Researches in Ecology, Environment
and Pollution (ed. Tilak, S. T.), 1989, pp. 153–157.
32. Mondal, S., Bhattacharya, K. N. and Mandal, S., in Aerobiology
(ed. Agashe, S. N.), Oxford & IBH Publ. 1997, pp. 401–
405.
33. Sathes, H. R., Rao, G. R. and Nair, P. K. K., Acta Bot. Indica,
1993, 25, 74–77.
34. Bhattacharya, A., Mondal, S. and Mandal, S., Environ Ecol.,
1997, 15, 283–287.
35. Johri, B. M. and Vasil, I. K., Bot. Rev., 1961, 27, 318–381.
36. Shivanna, K. R. and Johri, B. M., The Angiosperm Pollen Structure and Function, Wiley Eastern Ltd, New Delhi, 1989.
37. Vasil, I. K., Am. J. Bot., 1960, 47, 239–247.
38. Brewbaker, J. L. and Majumder, S. K., Am. J. Bot., 1961, 48,
457–464.
39. Brewbaker, J. L. and Kwack, B. H., Am. J. Bot., 1963, 50, 859–
865.
40. Lewis, D. H., New Phytol., 1980, 84, 209–229.
41. Mandal, S., Barui, N. C. and Ganguly, P. N., Sci. Cult., 1982,
48, 115–116.
42. Sidhu, R. J. K. and Malik, C. P., in Biotechnology and Ecology
of Pollen (eds Mulcahy et al.), Springer-Verlag, Berlin, 1986,
pp. 373–378.
43. Gupta, S., Bhattacharya, K. N. and Chanda, S., J. Palynol.,
1989, 25, 65–72.
44. Pal, J. K., Mandal, S. and Bhattacharya, G. N., J. Palynol., 1989,
25, 113–120.
45. Mondal, S., Bhattacharya, K. N. and Mandal, S., Indian Biol.,
1991, 23, 33–35.
46. Kaliamoorthy, S., Rangarajan, V. and Krishnamurthy, K. V., J.
Indian Bot. Soc., 1996, 75, 41–44.
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47. Bhattacharya, A., Mondal, S. and Mandal, S., Sci. Cult., 1997,
63, 143–144.
48. Rana, A., Singh, J. and Chauhan, S. V. S., Int. J. Mendel., 1996,
13, 15–16.
49. Heslop-Harrison, J., Heslop-Harrison, Y. and Barber, J., Proc.
R. Soc. London, 1975, 188, 287–297.
ACKNOWLEDGEMENTS. We thank University Grants Commission, New Delhi for providing financial assistance, Zoological Survey of India, Calcutta for identification of flower visitors and
Regional Sophisticated Instrumentation Centre, Bose Institute, Calcutta for scanning electron microscopy.
Received 6 June 2000; revised accepted 28 August 2000
Tree ring analysis of Larix griffithiana
from the Eastern Himalayas in the
reconstruction of past temperature
Vandana Chaudhary* and A. Bhattacharyya
Birbal Sahni Institute of Palaeobotany, 53, University Road,
Lucknow 226 007, India
Tree ring analysis of Larix griffithiana (Lindl. et
Gord.) Hort ex Carr., a subalpine deciduous conifer
growing in Sange, Arunachal Pradesh, Eastern Himalaya has been taken up to understand past climatic changes of this region. Rings in this tree have
been found very distinct, with clear demarcation of
early wood and late wood cells and have characters
suitable for dendroclimatic studies. Analysis of tree
growth and records of climatic parameters suggest
that May temperature is the most important factor
in controlling growth of this tree. Reconstruction of
May temperature using ring width data of this tree
has been done.
L. griffithiana (LAGR), a deciduous conifer is distributed at altitudes 2,400–3,650 m. Its provenance is from
eastern Nepal, extending through Darjeeling, Sikkim,
Bhutan and Arunachal Pradesh and continues up to NE
upper Burma and Chumbi Valley in Tibet4. It grows up
to 15–18 m in height with long pendulous branchlets
and mostly occupies steep slopes on morainic deposits
where drainage is good. The trees occur mostly in
patches, either forming pure forest or more often mixed
with other conifers.
Tree ring samples in the form of increment cores were
collected from LAGR growing in Sange, West Kameng,
Arunachal Pradesh (Figure 1). This site is characterized
by very open mixed conifer forest. Trees are tall and
straight with medium-sized girth (Figure 2). Associated
species are mostly silver fir and Rhododendron. Undergrowth is rich and represented by bamboo, fern, etc.
Soil cover is thin, but thick leaf cover and moss are present on the ground forming a mat. Twenty increment
cores were collected from 11 trees growing on the
southern slope of the hill at an altitude of 3320 m. In
most cases two cores per tree, one each from the opposite directions at breast height were collected. In at least
two cases, only one core could be collected, as the other
side was not approachable due to steep slope. Samples
were mounted and processed using standard procedure
of tree ring analysis. Details of the methods of tree ring
analysis can be found in several publications5–7.
Boundaries of rings in LAGR tree are very sharp and
there is a clear demarcation of early wood and late
wood (Figure 3). Each ring of the cores was dated to the
calendar year of its formation using cross-dating technique8. Ring width of each dated core was measured by
T HE available high-resolution climatic data from the
eastern part of the Himalaya is limited. Tree ring proxy
record seems to hold excellent potential to extend back
the existing meteorological records of this region. History of tree ring analysis in the Indian subcontinent,
especially from the western and central part of the Himalayan region has been reviewed recently1. Being under the influence of pronounced precipitation almost
throughout the year, with varying intensity, this region
is somewhat problematic for such studies. Under such
climatic conditions, trees are expected to have false or
multiple rings. However, recent exploratory studies2–3
from this region have indicated several suitable trees
and sites. It is a report on the prospect of reconstruction
of past temperature using tree ring width data of Larix
griffithiana from the Eastern Himalayan region.
*For correspondence. (e-mail: [email protected])
1712
Figure 1. Location of tree ring site and meteorological station.
CURRENT SCIENCE, VOL. 79, NO. 12, 25 DECEMBER 2000