pollen production in anemophilous trees
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Pollen production in anemophilous treesRafael Tormo Molina a , Adolfo Muñoz Rodríguez b , Inmaculada Silva Palaciso c &Francisco Gallardo López aa Department of Biology and Plant Production, Faculty of Science , University ofExtremadura , Avda. Elvas s/nb Department of Biology and Plant Production, Agrarian Engineering School ,University of Extremadura , Road to Cáceres s/n, 06071c Department of Electronic and Electromechanic Engineering, Agrarian EngineeringSchool , University of Extremadura , Road to Cáceres s/n, 06071, Badajoz, SpainPublished online: 01 Sep 2009.
To cite this article: Rafael Tormo Molina , Adolfo Muñoz Rodríguez , Inmaculada Silva Palaciso & Francisco GallardoLópez (1996) Pollen production in anemophilous trees, Grana, 35:1, 38-46, DOI: 10.1080/00173139609430499
To link to this article: http://dx.doi.org/10.1080/00173139609430499
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Grana: 35: 38-46, 1996
Pollen production in anemophilous trees
RAFAEL TORMO MOLINA, ADOLFO MUROZ RODRiGUEZ, INMACULADA SILVA PALACIOS and FRANCISCO GALLARDO LOPEZ
Torno Molina, R., hluiioz Rodriguez, A., Silva Palacios, I. & Gallardo Mpez, F. 1996. Pollen production in anemophilous trees. - Grana. 35: 38 46 ISSN 0017-3131.
A study was made of the total pollen production per individual tree in ten anemophilous arboreal species (including wild, cultivated and ornamental species) of considerable aerobiological importance: Pinus pinaster, Ulniirs minor, Juglam regia, Platanics liispaniea, Quercus rotundiJolia, Salix atrveinerea, Populus nigra. Aeer negundo, Olea eiiropaea and Fraximts angustijolia.
For each species three isolated well-shaped specimens of medium height were chosen, and the number of flowers per indibidual tree and the number of pollen grains per anther was estimated.
The values of total pollen production varied between a little over 1000 million grains in Jiiglans regia and more than 500,000 million in one single tree in Quercus rotitiidifolia. For the production of pollen grains per anther, the values oscillated betneen 3000 grains in Jiigluiis regia and 100,000 in Olea europaea. There is an exponential correlation betaeen the size of the anthers and the number of pollen grains they contain. A linear correlation is also evident between the volume of the tree crown and the total production of inflorescences, floners, anthers and pollen grains per individual tree. Based on this, a mean coefficient of the number of grains/meter of diameter of the tree cronn is obtained which varies between 3.4 x 10' for Juglaiis regia and 550.9 x lo* for Qrtercus rotriridifolia. The ratio between the number of anthers per inflorescence and the number of pollen grains per anther carries out a hyperbolic function; thus, the inflorescences nith the most anthers have the anthers with the least pollen and vice- wrsa. This ratio is also manifest between the number of grains per flower and the number of floaers per tree, as nell as the number of grains per inflorescence and the number of inflorescences per tree.
Rafael Toriiio hlolina & Francisco Gallardo Upe:, Departinen t of Biology arid Plant Production, Faculry of Science, University of Extreiiiadirra, Arda. Elws s/n, AdolJo Alir17oz Rodriguez, Departmiit of Biology and Plant Productivn, Agrarian Engineering Scliool, University of Extreniadura, Road to Cheeres sl., 06071, Iimiaatlada Siha Palacios, Department of EIeetronie and Electroniechanic Engineering, Agrarian Eugiiieering Scliool, Uiihersity of Extreniadura, Road to Giceres sin. 06071 Eadajoz. Spain.
Qlanuscript accepted 16 October 1995)
Anemophilous plants are characterized by high pollen pro- duction, as the vector of pollination they employ, the wind, is extremely haphazard and not specific. According to Faegri and van der Pijl(1979), the anemophily of these angiosperms is derived, and an increase in the production of pollen occurs in order to compensate for a reduction in efficiency.
Most of the scant research carried out in this area yield data on the amount of pollen produced per anther or flower in the species under investigation. Even fewer are the studies which give information about the total amount of pollen produced per plant, principally due to the arduous task of quantifying the total number of anthers per plant (Moore et al. 1991). There are also a few studies which estimate the total production from the amount of pollen deposited on the ground (Solomon 1979).
One of the first and also most complete studies of the amount of pollen produced by a plant, is that carried out by Pohl (1937). In this study, information is provided about the quantity of pollen produced per anther, flower, inflores- cence and branch in some anemophilous species. Data are also provided about the quantity of pollen per square metre of land surface produced by some plants by calculating the projection of the plant on the soil and the number of flowers per individual.
In 1933 Erdtman added a few more data to complete
Pohl's study (1937), and in 1969 he presented a table of 19 species for which he calculated the number of grains per anther, flower and ament, and established an index of relative pollen production, using the value of one as a reference for Fagtrs sylvatica. He affirmed that there is a clear tendency towards an increase in the production of grains of pollen in anemophilous plants. Hyde and Williams (1946) provide complementary contributions with an estimate of the pollen production per surface unit in Plantago Ianceolata, calculat- ing the number of inflorescences per square meter of land surface, the number of open flowers per inflorescence and the mean number of pollen grains per flower, giving a mean value of 40 x lo6 grains of pollen per square metre and day. Nair and Rastogi (1963) provide a further contribution by studying the pollen production of several species linked to allergy such as Clrenopoditrr~i albtim ( 133 pollen grains/anther) and Mortis alba (23,000 pollen grains/anther).
The production of pollen of the Poaceae family has been studied by several authors. Agnihotri and Singh (1975) find between 800 (Cjnodon ductyloii) and 13,000 (Secule cereule) grains per anther, and suggest that the total production of pollen depends directly on the size and length of the anther, calculating a value of 700-1200 pollen grains per millimeter of anther length. Smart el al. (1979) make an estimate o f the pollen production per anther and spike in 30 types of
0 1996 Scandinavian Unhersity Press. ISSN 0017-3131 Grana 35 (1996)
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Polleit production in mieriiopliilorrs trees 39
on the main branches, all main branches were counted, as \!ell as the number of bunches on 5 branches (Table I, column 2) and the number of inflorescences per bunch in 20 bunches.
grass. By counting the number of spikes per square metre they arrive at an estimate of total production of pollen per surface unit between spikes of gramineae. Thus, for Lolirrrit pereitrte they give a value of 2.11 x IOl3 grains per season and hectare, which is equivalent to a mass of 464 kg of pollen per hectare. Joppa et al. (1968) determine the total production of grains of airborne pollen of different types of Triticiuii from the number of fertile flowers and the percent- age of extruded anthers. Finally, Sree Rangaswamy and Raman (1973) prove that in Oryzu sufim polyploidy causes the number of pollen grains and the size of the anthers to increase, while the ratio between the two decreases.
Janaki Bai and Subba Reddi (1980) and Subba Reddi and Reddi (1986) determine the pollen production per anther of several angiosperms from India. Like Agnihotri and Singh (1975), they conclude that the pollen production, besides varying greatly from one species to another even within the same genus, is directly related to the size of the anther and inversely related to the size of the pollen grain and that, therefore, those species with large anthers and small pollen grains are the most productive ones.
Although a plant’s total production of pollen grains is influenced by various factors (Stanley & Linskens 1974) and also varies from one year to the next (Rogers 1993) it is most important to have an estimate of the total production of pollen per plant, not only from an aerobiological but also an agronomical standpoint, as the production of seeds often depends on the production of pollen (Faegri & Iversen 1989, Cour & Van Campo 1980). Thus, Holm (1994), to give an example, demonstrates that, by adding a supplementary amount of pollen to Bettrlu, an increase in the quantity of seed produced can be obtained.
MATERIALS AND METHODS
In order to carry out this study, ten anemophilous arboreal species of considerable aerobiological importance \ w e selected, including wild, cultivated and ornamental ones: Piiius pinaster, Ulntirs minor, Juglaiis regia, Plaraiiirs Irispanica, Qrrercrrr rotuiidiJolia, Sali-r arroci- nerea, Popiilus nigra, Acer negimdo, Olea europaea and Fruxinirs aiigtistifoliu. The locations where they nere harvested are given in Annex I.
In each species, three isolated trees were chosen that aere in good health and aell-shaped and they were measured for height and diameter of the tree crown.
Count of the number of inflorescences
In the case of species nith a high number of inflorescences arranged on the main branches Piizus pinaster (strobili groups), Ulmus ininor, Platanus hispatiicu, Populirr nigra, and Su1i.r atrocinereu, first the main branches \rere counted (Table I, column 1) and then a sample of 2-5 branches was selected and a count was taken of all their inflorescences (Table I, column 3).
In the case of Jugluns regia in which the number of inflorescences per tree is small, all inflorescences per specimen were counted (Table I, column 3). In the two ewrgreen species studied, Quercus rotrindiJoIia and Olea europaea, whose aments and racemes, respect- ively, are arranged on the surface of the tree crown and also grouped together, all groups of inflorescences within a giben area nere counted (1 m2) and the results were extrapolated to the total estimated surface (Table I, column 2). Finally, in Fruxitius angusfi- folia and Acer negiurdo, nhose inflorescences are grouped in bunches
Count of the number of flo\vers and anthers
Whenever possible 20 infloresences scattered throughout the tree were selected (except in Jitglms regia where 5 aments were counted) and the number of flowers per inflorescence was ascertained (strobili group, raceme, aments, or glomerules - Table I, column 4).
In those species whose flowers do not have a set number of anthers (Qzcerncs rorrcirdfo!ia, Ulmrrs niinor, Acer riegmdo, Jirgluiis regiu and P O ~ Z ~ J ~ S nigru) a flower was chosen from the middle of each of the 20 inflorescences selected, and the number of anthers was counted. In Pinus pinaster the number of microsporophylls per strobilus was counted, and in Platariirs hisparzicu the number of anthers per inflorescence, since ahen the inflorescences are handled the anthers fall from the floners.
Count of the number of pollen grains per anther
The pollen grains were counted by using 5 anthers from different flowers for each one of the three trees which had been previously measured (Table I, column 6) . Basically, the method used was that of Cruden (1977). The anthers aere obtained from closed floners kept in 70% ethanol that were washed in distilled water, measured, and placed in test tubes. They were taken apart Nith the aid of a glass rod and in most cases the pollen grains were suspended in Icc of distilled water. From this concentrate, five drops of 10 p1 tiere remoked and then the pollen grains were counted (Table I, column 7).
Estimate of the total production
In order to estimate the total production of pollen per individual plant, first the total number of anthers per tree was calculated (Table 11, column 5 ) by multiplying the number of total inflores- cences by the a\erage number of flo\rers per inflorescence and by the average number of anthers per flower; then the result was multiplied by the average number of pollen grains produced per anther. For each tree an estimate was made of the production of pollen grains per anther per metre of diameter of tree crown.
Calculation of the correlation coefficients
The surface of the tree can be estimated as the lateral surface of a cylinder whose base is a circle with the same diameter as that of the tree crown and whose height is that of the height of the tree (2nr/z), or we can estimate it by considering the surface of a sphere whose diameter is that of the crown (4x9). Likewise, the volume of both geometric shapes can be calculated ( d l z for the circle and 4/3d for the sphere). From these data the correlation coefficients Bere calculated, and their statistical significance (p[rl=O) from the total production per tree of inflorescences, floners, anthers, and pollen grains \\ith the dimensions of the tree (height and diameter of the crown), the surface and the volume of the tree crown considered both as a sphere and a cylinder.
The correlation betneen the dimensions of the anthers and the production of grains per anther nas calculated, as aell as the correlation between ten pairs of ratios of production: grains/ anthers, grains/flower, grainsfinflorescence, grains/tree. anthers/ floner, anthers/inflorescence, anthers/tree, flowers/inflorescence, flo\vers/tree, and inflorescences/tree.
By using the mean values per tree of the number of inflorescences per tree, flowers per inflorescences, anthers per floaer, and grains per anther, a Factor Analysis \\as carried out following the 4m program of the BMDP statistics package. In order to use the values
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**
Tabl
e I.
Dat
a for e
uch
tree
(ra
nge.
tir
em a
rid s
tdm
1 cle
viutio
rr) .
s .S
a. tre
e, I
. to
tal
amou
nt of
bran
ch,
2. n
umbe
r of
twig
s w
ith i
nflo
resc
ence
gro
ups,
3. nu
mbe
r of
inflo
resc
ence
s (or
stro
bili
grou
ps in
Piri
ris)
per
bran
ch.
(num
ber
of i
nflo
resc
ence
s per
trcc
in
JU
~~
JK
Y)
or n
umbe
r of i
nflo
resc
ence
s pcr
gro
up o
r inf
lore
scen
ces (
Qiic
rcus
and
Olc
u), 4
. nu
mbe
r of
flow
ers p
er in
flore
sccn
cc (or
num
ber of
stro
bili
per s
trobi
li gr
oup)
. 5, n
umbe
r of a
nthe
rs p
er
flow
er (o
r mic
rosp
orop
liylls
in P
imi.?
, num
ber
of n
ntlie
rs p
er in
flore
scen
ce in
P/m
mis
), 6. an
ther
leng
th in
mm
, 7. n
umbe
r of
pol
len
grai
ns p
er a
nthc
r or m
icro
spor
ophy
ll.
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(4
7.4)
(6
-22)
13
0 (4
.6)
(8-2
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15.1
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2.7
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(37.
800-
56,5
00)
47.5
560
(4,5
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) 2
31
(60-
120)
92
.0
(25.9)
(1-8
) 3.5
(2
.4)
(7-1
9)
13.4
(3.3
) 2
(2.2
-28)
2.
5 (0
.27)
( 1
8.00
0-77
.000
) 42
.240
0 (1
4.429
0)
Oho
I 19
M)
(10-
30)
18.0
(7
.5)
(10-
21)
16.8
(34)
2
(2.5
-2.7
) 2.6
(0
.07)
(b
i.Oo0
-1~6
,oO
o)
9~?4
o.o
(17.
936.
0)
3 31
(6
0-12
0)
866
(25.
4)
(5-1
4)
9.3
(3.5
) (1
4-22
) 17
.0
(3.0
) 2
(2.0
-2.7
) 2.
5 (0
.30)
(31.000
87.00
0)
~2.7
20.0
(14
.701
.0)
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Pollen prodiictiori iti atietiiopliiloiis trees 41
Table 11. Total data for each tree. a. tree, 1. height in meters, 2. diameter in meters, 3. number of inflorescences (x lOOO), 4, number of flowers ( x IOOO), 5. number of anthers (x lOOO), 6. number of pollen grains (x 1,000,000), 7. number of anthers per inflorescence, 8. number of pollen grains per inflorescence (x lOOO), 9. number of pollen grains per flower (x lOOO), 10. number of pollen grains per meter of crown diameter ( x 100,000,000).
Taxon a 1 2 3 4 5 6 7 8 9 10
Pinus
Ulr1nrs
Juglans
Platarriu
Quercus
Populus
Salk
A cer
Olea
Fraxinus
1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3
6.5 7.0 5.5 4.2 8.0 8.0 5.0 6.5 6.0 6.0 6.5 7.0 4.0 5.0 4.5 8.0 9.0 8.0 6.0 3.5 3.0 6.5 5.0 6.0 3.5 3.5 4.0 7.0 5.0 7.0
4.5 5.8 7.7 10.5 5.5 6.5 4.5 6.8 4.3 6. I 5.3 8.3 11.2 10.0 11.5 7.6 6.4 8.2 5.8 5.3 6.8 7.0 5.6 5.4 6.1 4.2 5.1 8.0 6.5 7.5
4.7 8.1 6.2 17.4 8.4 11.6 0.1 0.3 0.3
11.1 8.2 19.5 378.7 2 10.4 567.0 10.1 6.7 6.0 38.1 20.1 33.1 47.2 33.4 15.3 34.2 11.7 12.4 111.9 9.9 31.5
151.3 23 1.6 181.7 386.3 150.4 187.1 20.9 55.3 53.9 658.2 415.5 1291.8 6891.9 3997.2
11,624.3 403.0 295.8 283.8 9081.6 5617.0 6803.5 632.6 463.8 174.1 574.6 194.5 174.5 1689.5 132.6 535.7
6702.0 8802.6 830-1.6 1583.7 586.4 748.4 320.3 7 12.9 835.8 3620.3 2285.5 7121.4
46,175.6 22,184.2 101,131.6 6423.4 3786.5 4651.0
18,163.2 11,231.0 13,607.1 2591.7 2132.3 800.2 1149.1 388.9 319.0 3319.0 265.2 1071.4
20.9 32.3 22.2 8.0 5.0 5.8 1.8 2.3 2.8
114.9 126.3 250.6 130.1 109.4 633.5 47.7 41.3 36.0 125.8 133.7 113.0 250.1 37.0 15.2 108.3 40.7 29.1 160.7 11.2 56.5
1439.8 1083.0 1348.2 91.0 69.8 61.8
3168.4 2376.2 2932.6 326.1 277.2 365.2 121.9 108.3 178.3 634.4 564.5 712.4 476.6 559.6 41 1.4 53.9 63.9 52.4 33.6 33.2 28.2 30.2 26.8 34.0
4497.8 3968.1 3596.9 462.0 595.6 502.8
21,208.5 7755.9 9806.6
10,353.3 1532 1.4 12,853.6 343.5 519.8
1 117.2 4709.9 6159.6 5978.7 3301.9 6710.7 3416.3 5298.9 1109.6 995.0 3166.5 3472.7 2349.6 1436.2 1132.0 1792.5
138.4 139.2 121.9 20.8 33.3 31.0 86.1 42.1 51.8 174.6 301.0 193.6 18.9 27.4 54.5 118.0 139.7 126.9 13.9 24.0 16.6 395.1 79.9 87.3 188.5 209.2 166.6 95.1 84.5 105.4
46.5 55.6 28.8 7.7 9.1 8.9 4.0 3.4 6.5
188.4 238.3 302.0 116.1 109.4 550.9 62.7 64.6 43.9 217.0 254.2 166.2 357.4 66.1 28.1 177.5 96.9 57.0 200.9 17.2 75.3
of anthers per flower and flowers per inflorescence in Platanus hispanica, 5.5 was considered as the mean value of the number of anthers per flower, using as a guideline the results of Rocha Afonso (1990). From these the number of flo\\ers per inflorescence was calculated since the number of anthers per inflorescence was knowm.
RESULTS
The dimensions of the trees studied (height and diameter of the tree crown) appear in columns 1 and 2 of TableII, respectively.
The number of inflorescences, flolkers, anthers, and pollen grains per anther varies considerably from one species to another (Table I). The number of inflorescences per terminal branch (TableI, column 3) is very variable in the trees under study. The inflorescences in Qirercirs, Acer, Olea and Frasitiiis, which always number less than 50, appear on short little branches which grew the previous year. On the other hand, in Pitiirs, Ultsirs, Platatiris, Popirliis and Salix they appear on older and more fully grown branches and therefore there can be as many as a thousand. In Jiiglatis their number is small on the entire tree, giving a total of 85 to 300.
The number of flowers per inflorescence (Table I, column 4) barely reaches 50 in Pitiirs (strobili per group), Ulniiis, Qiierciis, Popiiliis, Acer, Olea and Fraxinirs; but it is much higher in Jiiglans and Salix, reaching more than 300.
The number of anthers per flower (Table I, column 5 ) is always 2 in Salix, Olea and Fraxiniis; oscillates between 3 and 5 in Uliiiiis and Acer; becomes steadily higher in Qiierciis, Jiitiglatis and Popriliis (where it can reach as many as 25); and the number of microsporophylls per strobilus reaches as many as 45 in Pitiits. In the case of Platattris, where only the number of anthers per inflorescence could be counted, it oscillates between 100 and 450 per inflorescence.
The number of pollen grains per anther or microsporophyll (Table I, column 7) gives minimum values in Pitiiis, Jiigloru and Qirercirs, where it never reaches 10,000. The maximum values appear in both of the Oleaceae under study (Oleo and Fraxitiiis). In the former, anthers with more than 100,000 grains were frequently found. Nevertheless, in a population of Acer as many as 200,000 grains of pollen per anther have been counted.
Total production
The total production of inflorescences per tree oscillated between approximately one and three hundred in Jtiglais, and up to half a million in Qiiercirs (TableII, column 3) , but the most frequent value for the rest hovers around tens of thousands of inflorescences per tree.
The total number of flowers per tree (Table 11, column 4)
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R Tornio hfoliria et al. 42
1m
tD0
10
1
Fig. 1. Total pollen production per tree, thick line is the mean, thin lines are maximum and minimum.
is again minimal in Jirglaiis (20,000-55,000) and climbs as high as several million in Qicercus and Salix, due in the latter case to the high number of flowers per inflorescence. The total number of anthers per tree (TableII, column 5) is minimal in Ulimls, Jiiglaris, Olea and Fraxiriirs in which it is around half a million; and maximal again in Qciercus, with as many as 100 million.
The total production of pollen grains per tree (Table I, column 6 and Fig. I) oscillates between a little over one thousand million for the above mentioned species and around 500,000 million for Qirerciis reaching above one hundred thousand million in Platamis, Salix and some specimens of OIea and Fraxiriirs. By dividing this amount by the diameter of the tree crown we arrive at an estimate of the quantity of grains of pollen produced per tree regardless of the size of the tree crown. This value oscillates between 3.4 x lo8 in Jirglaris and 550.9 x 10' in Qirerciis (Table 11, column 10).
Correlations betaeen the dimensions of the tree and the production of inflorescences, floners, anthers and pollen grains
The total productions of inflorescences, flowers, anthers and pollen grains are all logically correlated as one is multiplied by the next to obtain the total production Table 111.
The height of the tree has a negative significant correlation with the total number of flowers. In other words, the taller the tree the more proportionally reduced is the number of flowers. In contrast, the diameter of the tree crown has a
positive significant correlation with the total number of inflorescences, floibers, anthers, and pollen grains.
There appears to be no correlation between the surface of the cylinder and the production of the trees, but there is a positive significant one with the surface of the sphere. There are positive and significant correlations betneen the volume of the cylinder and the production of inflorescences, anthers and pollen grains, but they are inferior to the correlations of the surface of the sphere. The highest correlation with the production of inflorescences, flowers, anthers and pollen grains are with the volume of the sphere whose diameter is the diameter of the tree crown.
Correlation between the number of pollen grains per anther and the length of the anther
The average length of the anthers or microsporphylls (Fig. 2, Table I, column 6) varies betneen 1 and 2mm for Piriiis piiiaster, U h r s iiiiiior, Qiierciis rotiwdifolia, Poptihis iiigra and Sa1i.r atrocinerea; between 2 to 3 mm for Jiiglaris regia, Platmiis hispanica, OIea eiiropaea and Fraxiriirs angustifolia; and between 3 and 4.5mm for Acer riegiriido. A positive significant correlation has been found between the length of the anthers and the number of grains produced per anther (r-0.6636, p=O.OOO), using a total of 150 data ( 5 anthers per tree in a total of 30 trees). If we calculate the correlation between the length of the anthers and the decimal logarithm of the number of pollen grains, we obtain a higher value (r=0.6934, p=O.OOO - see Fig. 2), which indicates an expo- nential ratio between the two. By calculating the linear regression t\e find that logy=3.1895+0.4687x (y being the dependent variable: the number of grains per anther; and x the independent variable: the length of the anther).
Correlations between the ratios graindanther, grains/flouer, graindinflorescence, graindtree, antherdflow ers, anthers/ inflorescence, anthersltree, flow erslinflorexence, flow ers/tree and inflorescences/ tree
There is a significant (ptO.05) positive and linear correlation between the number of grains per flower and of anthers per flower; between the grains per inflorescence, anthers per inflorescence and flowers per inflorescence; and between the grains per tree, anthers per tree, flowers per tree and inflores- cences per tree.
By calculating logarithms these correlations are maintained and other significant correlations, although negative ones, also become apparent (Table IV): The number of pollen
Table 111. Correlatioiis between the total anioirrit of itflorescences (inflor.), flowers, anthers arid polleri graiiis per tree with tree height, crown diariieter, crowi siirface (as cilirider aiid sphere). arid crow1 vohaiieri (as cilirider and sphere) in the stirdied trees. Each pair of data represent the correlation coefficient and the probability (plrl-0).
Height Crown diameter Cilind. surf. Sphere surf. Cilind. kolume Sphere volume
Inflor./tree -0.2790 0.135 0.7149 0.000 0.2376 0.206 0.7764 0.000 0.5474 0.002 0.8224 0.000
Anthers/tree -0.2594 0.166 0.6367 0.000 0.1981 0.294 0.6980 0.000 0.4932 0.007 0.7467 0.000 Pollen grains/tree -0.1763 0.351 0.5203 0.003 0.2250 0.232 0.5465 0.002 0.4362 0.016 0.5665 0.001
Flowers/tree -0.3981 0.029 0.4741 0.008 -0.0019 0.979 0.5140 0.001 0.2620 0.162 0.5472 0.002
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Pollen production in aiieinophilous trees 43
Pinus + Vmus 0 Juglans = platanus x Quercus I A S a h n Acer 3 Olea Frm.nus - rearession
Fig. 2. Relationship betaeen the number of pollen grains per anther and the anther length in ten trees.
grains per anther decreases significantly when there is an increase in the number of anthers per flower, in the number of anthers per inflorescences, or in the number of anthers per tree.
Furthermore, the number of grains per flower significantly decreases when there is an increase in the number of flowers per inflorescence, of flowers per tree or of inflorescences per tree. The number of grains per inflorescence significantly decreases when the number of flowers per tree or of inflores- cences per tree increases. The number of anthers per flower significantly decreases when the number of flowers per tree or the number of inflorescences per tree increases. The number of anthers per inflorescence significantly decreases when the number of inflorescences per tree increases. And finally, the number of flowers per inflorescence decreases when the number of inflorescences per tree increases. This type of ratio which is obtained by using logarithmic values and in which by increasing one value the other decreases, carries out a hyperbolic function expressed as YX=c, c being the constant that can be calculated as the mean product of X times Y (see Fig. 3 which shows the ratio between the number of pollen grains per anther and the number of anthers per inflorescence).
The results of the Analysis of Factors appear in Fig.4.
pollen graindanther (x 1.ooO) 120 I
I
l W I 80
Pins + Ulrnus 0 Juglans AS& oAcer OOlea t Fradnus hyperbola
platanus x Quercus * PopUlUS
Fig. 3. Relationship betaeen the number of pollen grains per anther and the number of anthers per inflorescence in ten trees.
0 0
8
w w 0 m 0 0 0 - o m 0 0 000000 179999
000000 I I I
- f F . o Q \ o w o W m O C Q O N O
0000000 a \ 9 9 Y 0 ? S
00000000 I I I I I
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44 R Torriio hloliiia et al.
4
3
2
1
0.5
0
-0,s
-1
p<
X
X I
-05 0 0 5 1 factor 1
factor 2 3c
factor 1
* ibwenlnfbr. Oanthersfiower #pollen grainslanthei
factor 1
-1 0 1 2 3 -6
factor 1
0 Pinus
0 Jughns Piatanus
XQuercus + Populus ASalix
T Fraxinus
Fig. 4. Result of the Factor Analysis using four variables (number of inflorescences per tree, number of floners per inflorescence, number of anthers per flower and the number of pollen grains per anther), and 30 trees of ten species. Variables are represented in the two upper scater diagrams and the trees in the two lower ones. The tno diagrams on the left using factors 1 and 2, and the two on the right using factors 1 and 3.
The accumulated proportion for the first three axes is 37.8, 66.4 and 91.6, respectively. They represent the 4 variables used (inflorescences per tree, flowers per inflorescence, anthers per flower, and grains per anther) and the 30 trees studied, according to the factors 1, 2, and 3. Usually the trees of the same species are together, except for tree 1 of Acer riegiiiido, which grew separate from the other specimens. The four variables are strongly segregated. For seven of the ten species studied, one factor appears to be the most influential on the total production of pollen grains. Piriiis piriaster stands out because it possess a large quantity of microsporophylls per strobilus; Sali.\- atrociiiera and Jiiglaris regia are segregated for their high production of flowers per inflorescence; Olea eiiropaea, Frasiriiis arigiistifolia and one specimen of Acer riegiiiido stand out for their high production of grains per anther; the rest have high production of inflorescences (Qwrciis rotuiidifolia) or they have a stable production as far as inflorescences, flowers, anthers, and pollen grains per anther (Acer itegiirtdo, Platmtiis Iiispariica, Ulriiiis riiirior and Popiihis iiigra).
DISCUSSION AND CONCLUSIONS
Knowing the total pollen production per plant is useful in order to estimate the number of pollen grains that could be
in the air during a certain season, once the density of plants per surface unit is known. It can also be used as an estimate of the production of seeds (Campbell & Halama 1993, Allison 1990), as the efficiency of anemophilous pollination decreases with the reduction in the concentration of airborne pollen (Whitehead 1983).
Pohl(l937) gives some values for the total pollen produc- tion per plant in several herbaceous species which vary between almost 3 million and a little more than 1300 million, the maximum value pertaining to Merciirialis ariiiiia.
Obviously, woody plants produce larger quantities, as the data from this research project give values always higher than 1000 million grains per plant. The number of pollen grains per anther is also very variable. The same author gives the following values for different species of the same genera studied in our research project: Fraxbtts excelsior 12,500, Qiierciis sessilifora 5000, Acer plataiioides 1000. However, in our study the following values were obtained: Fraxbiiis arigiistifolia, between 18,000 and 87,000; Qiierciis rotiirrdfolia, between 1530 and 9800; Acer riegiiiido, between 12,700 and 217,500.
Erdtman (1943) gives values for pollen production per flower for different trees, such as Piriiis sjhestris (158 lo3 per strobilus) and Qiierciis sessilifora (41 x lo3). In this
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Pollen prodiictioti it1 atieniopliiloris trees 45
research project, we found the following values for the species studied from these genera: Pitiiis pitiaster, between 244 x lo' and 280 x lo' per strobilus and bet\\een 340 x lo3 and 1100 x lo' for Qiierciis rotiitidfolia.
Since the total production of pollen grains per tree is positively correlated with the diameter of the tree crown and not with the height, this could indicate that the amount of available light is a limiting factor in the production of inflorescences and flowers. It could also lead us to believe that height might act in a negative way, as is evidenced by the negative and significant correlation between the height and the number of flowers per tree (Table 111).
The existence of a cubic ratio between the dimensions of the tree crown and the total production of pollen grains indicates that the distribution of inflorescences on the tree branches is homogeneous. This appears logical in deciduous trees, but not in evergreens (Qiierciis rotiiridfolia and Olea europuea) whose inflorescences are arranged on the surface of the tree crown. Perhaps more studies should be carried out on the evergreen species.
The correlation between the size of the anthers and the quantity of pollen grains they contain has already been demonstrated by other authors (Agnihotri & Singh 1975, Subba Reddi & Reddi 1986). However, this ratio is not linear, but rather exponential. According to our data, the number of pollen grains ( y ) in terms of the size of the anther inmm (x) can be calculated with the formula: y=l , 547.16 x 2.94'.
The existence of a hyperbolic ratio between the relative productions of the different aspects of production (anther, flower, inflorescence, tree) leads us to believe that in the anemophilous arboreal species there is a constant value for pollen production. As the number of pollen grains per anther, anthers per flower, flowers per inflorescence, and inflores- cences per tree varies considerably, there is a tendency to compensate by increasing one or reducing the other, so that the resulting product is generally within some defined mar- gins. Thus, some species would have a tendency to increase the number of inflorescences in order to compensate for the small number of flowers per inflorescence or anthers per flower or grains per anther, as is the case with Querciis rotiitidfolia; others would produce a large quantity of flowers per inflorescence, such as Salix atrocitiera and Jiighns regia, which have a small number of flowers per inflorescence or pollen grains per microsporophyll, respectively; others would increase the number of anthers per flower or microsporo- phylls per strobilus. Other species would considerably increase the number of pollen grains per anther, such as Olea europaea and Fraxiiius atigristfolia, which have a small number of anthers per flower. Finally, the more or less well- balanced species as far as the production of pollen grains anthers, flowers or inflorescences is concerned remain, such as Plataiiiis Iiispanica, Uliiiiis Inittor, and Poprrlris nigra.
ACKNOWLEDGEMENTS
This aord has been supported by the Regional Government (Junta de Extremadura, Consejeria de Educacibn) by the research project EIB94-12. We wish to thank JosC Luis Oncins Martinez for the translation.
SPECIMENS INVESTIGATED
Piriur pinaster Aiton: Badajoz, University campus, 8.3.94. Ulriiiis minor Miller: Badajoz, Guadiana river, 2.2.94. Jugluris regia L. Badajoz, road to Bbtoa, 1.3.94. Pluturius Iiispurzica Miller ex hliinch.: Badajoz, Valdepasillas (trees 1 and 2), and University campus (tree 3), 14.3.93. Qiiercus rotirrzdiJoliu Lam.: Badajoz, Bbtoa, 22.3.94. Popirhrs riigru L.: Badajoz, Talaera la Real, 3.3.94. Sa1i.r atrociiierea Brot.: Badajoz, Guadiana river, 23.02.94. Arer rzegimdo L.: Badajoz, Valdepasillas, (tree 1); University campus (trees 2 and 3), 23.2.94. Olea eriropaea L.: Badajoz, road to Valverde de Leganis, 5.5.9-1. Fraxinus aiigttsfijolia Vahl Badajoz, Bbtoa, 14.1.93.
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Faegri, K. & hersen, J. 1989. Textbook of pollen analysis. 4th ed. K. Faegri, P. E. Kalland & K. Krzywinski. - J. \Viley & Sons, Chichester, New York, Brisbane, Toronto, Singapore.
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