Bot. Bull. Acad. Sin. (1997) 38: 57_62

Tsou et al. — Airborne pollen in Taichung, Taiwan

Aeropalynological investigation in Taichung, Taiwan,

1993_1995

Chih-Hua Tsou¹, Ing-Jen Tseng, Rey-Feng Lin, and Hsin-Yu Hong

Institute of Botany, Academia Sinica, Taipei, Taiwan, Republic of China

(Received September 14, 1996; Accepted November 23, 1996)

Abstract. The airborne pollen spectrum was investigated in Taichung, Taiwan, in two consecutive years using a 7-day volumetric recording trap. In total, 323,745 pollen grains of seed plants and fern spores were counted, with a mean of pollen concentration of 30.8 grains/m³. In the course of a year, airborne pollen was most abundant in spring and least in summer. In dry days from late March to mid April, the pollen concentration usually remained around 1,000 to 2,000 grains/m³ for two or three hours in the morning. During these two years, the highest hourly pollen value was recorded during 11_12 A.M., on 15 April 1994, with a mean of 5,306.7 grains/m³. The pollen spectrum obtained did not reflect the floristic composition of Taichung city. The important pollen taxa were Broussonetia (66.83%), Casuarina equisetifolia (5.66%), Trema orientalis (5.02%), Poaceae (4.15%), Humulus scandens (2.77%), Alnus (1.99%), Morus (1.38%), Mallotus (1.14%) and Macaranga (1.04%). Most of them are common wild Amentiferae plants in lowland Taiwan. Broussonetia is extremely important for future studies of pollen allergy in Taiwan, not only for the allergenicity of its pollen, but also for the superiority of its pollen productivity and pollen dispersibility.

Keywords: Aeropalynology; Broussonetia; Taichung; Taiwan.

Introduction

Chao et al. (1962) conducted the first study of airborne pollen in Taiwan. Huang (1982) and Tsou (1982) reviewed the seven investigations in this field published in Taiwan during the period from 1962 to 1982. Only two more investigations have been completed (Chen and Chien, 1986; Peng, 1994) since then. Essentially, most of these works were designed to provide basic information for allergenic researches. Of these original investigations, most were undertaken in Taipei City and its suburban areas in northern Taiwan, and only one was sited central Taiwan. From 1992 to 1995, an integrated aeropalynology project was supported by the National Science Council, Republic of China. Six collection sites were established at different times in the various parts of Taiwan (N, W, SW, S, E, SE), and were taken charge of by different principal investigators. In this report, we shall present the results of a daily, two-year investigation from the western collection site of this integrated project.

Materials and Methods

Airborne palynomorphs were collected in Taichung city from 1 May 1993 to 30 April 1995, using a seven-day volumetric recording trap. The trap was placed 14 m above the ground on the roof of a four-story building in National

Chung-Hsing University (10 m asl., 24°07'N, 120°40'E). The adhesive layer on the cellophane tape was a mixture of gelvatol (35 g), glycerol (50 ml), phenol (2 g), and distilled water (80 ml). The air flow rate was adjusted to 10 l/min, and the moving rate of the tape was 2 mm/h. Finally, one 48 mm long segment of the tape was obtained for each daily collection and was mounted as a permanent slide.

Pollen grains of angiosperms and gymnosperms and fern spores collected were identified and counted on an hourly basis at 400× magnification. Besides referring to the Pollen Flora of Taiwan (Huang, 1972) and the Spore Flora of Taiwan (Huang, 1981) for identification, pollen grains and fern spores were collected fresh from more than 100 species growing in the vicinity of the trap to make reference slides. Twenty-four transverse travels were observed for a daily slide, i.e., one travel per hour. The total count for each hour was then converted by multiplying an adjusting factor (total area/observed area).

The vast majority of the woody plants growing in the vicinity of the collection site were cultivated ones. Wild individuals were comparatively much fewer, being found only along roadside and in small abandoned patches scattered in the city. The closest natural vegetation was more than 6 km away.

The meteorological data of Taichung used in the present report were obtained from the Central Weather Bureau, R. O. C. The Taichung meteorological station is about 2.5 km away from our pollen collection site.

¹ Corresponding author. Fax: 886-2-7827954; E-mail: botsou@ ccvax.sinica.edu.tw

Botanical Bulletin of Academia Sinica, Vol. 38, 1997

(of more than ten families) (see Table 1). Of all these families, Moraceae was decisively dominant, accounting for 70.98% of the total grains; Casuarinaceae and Ulmaceae, though taking the second and the third positions respectively, each representing only 5.66% and 5.20% of the grains.

Pollen and spores from more than 110 genera were identified. The percentage representations of the ten most significant taxa are as follows: Broussonetia 66.83%, Casuarina 5.66%, Trema 5.02%, Poaceae 4.15%, Humulus 2.77%, Alnus 1.99%, Morus 1.38%, Mallotus 1.14%, Macaranga 1.04%, and Bischoffia 0.98% (Figure 2). They were also very important in an earlier aeropalynological investigation conducted in northern Taiwan (Peng, 1994), in which they ranked 1^st, 6^th, 2^nd, 7^th, 9^th, 15^th, 13^th, 5^th, 6^th, and 18^th, respectively. Two basic patterns of pollen representation in the air throughout a whole year can be recognized in the pollen calendar. Broussonetia, Casuarina equsetifolia, and Trema orientalis conform to the first pattern—their pollen grains appear in one or two short-sustaining but strong concentrations in a year (Figure 3). The second pattern is found in the remaining seven taxa—they have many peaks throughout the year (Figure 4). It is notable that three of these seven taxa, Bischoffia, Humulus, and Macaranga are each represented by only one species on Taiwan Island.

Among these ten important taxa, Mallotus, Macaranga, and Bischoffia are members of Euphorbiaceae, and their pollen grains are tricolporate. The remaining seven taxa are anemophilous and produce porate pollen. Except for Poaceae, all of them are of the Hamamelidae. The porate pollen produced by the six Hamamelidae taxa are small or medium in size, each having an air chamber inside its 2_5 pores; among them, the genus Broussonetia, represented by B. kazinoki and B. papyrifera in Taiwan and also in Taichung, is newly found to be an important pollen contributor in Taiwan. Broussonetia pollen amounted to 73.7%

Results and Discussion

During the two consecutive years from 1 May 1993 to 30 April 1995, a total number of 323,745 pollen grains and fern spores were collected. Of them, 164,541 grains appeared in the first year, with a pollen concentration of 31.3 grains/m³ on average; in the second year, 159,204 grains were counted, averaging 30.3 grains/m³. The pollen spectra of the two years are rather similar in both pollen contributors and their individual significance (Figure 1 & Table 1). The pollen concentration was rather low on most days. It was lowest in January, averaging only about 3 grains/m³, but increased greatly in March and April with the mean rising to around 120 grains/m³. The highest daily peak in a year was recorded on April 3, 1994 with a daily mean of 627 grains/m³ and on March 23, 1995 with 833 grains/m³. On dry days from late March to mid April, the pollen concentration usually remained around 1,000 to 2,000 grains/m³ for two or three hours in the morning. On an hourly basis, the highest value appeared during 11_12 A.M. on 15 April 1994. In that one hour period, 0.6 m³ air was sucked and 3,184 grains were collected, with a mean of 5,306.7 grains/m^3.. 97% of these 3,184 grains was of Casuarina equsetifolia. Since a tree of Casuarina equsetifolia stood just 10 m away from the trap and no other casuarina individuals were nearby, this pollen peak must be attributed to a sudden burst of the abundant anthers produced by that casuarina tree.

In terms of plant habits, arboreous palynomorphs including the spores of tree ferns were dominant; they comprised about 89.95% of the total grains. Grass pollen amounted to 4.15% only. The remaining 5.90% was contributed by herbaceous plants (incl. herbaceous ferns). Taxonomically, the palynomorphs collected included 3,088 (0.95%) gymnosperm pollen grains (belonging to three or four families), 318,944 (98.52%) angiosperm pollen grains (of more than 48 families), and 1,713 (0.53%) fern spores

Figure 1. Daily pollen concentration in the atmosphere in Taichung, Taiwan, from 1 May 1993 to 30 April 1995, showing in two yearly curves.

Tsou et al. — Airborne pollen in Taichung, Taiwan

Table 1. Annual totals and percentages of daily pollen counts in Taichung, Taiwan, from May 1, 1993 to April 30, 1995.

Item 1st year % 2nd year % Sum % Rank

Gymnosperms 2233 1.357 855 0.537 3088 0.954

Cupress./Taxodiac. 1754 1.066 432 0.271 2186 0.675

Cryptomeria 144 0.088 20 0.013 164 0.051

Pinus 335 0.204 403 0.253 738 0.228

Angiosperms 161098 97.908 157846 99.147 318944 98.517

Amaranthaceae 64 0.039 16 0.010 80 0.025

Ilex 36 0.022 44 0.028 80 0.025

Asteraceae 1983 1.205 1035 0.650 3018 0.932

Alnus 3783 2.299 2655 1.668 6438 1.989 6

Brassicaceae 527 0.320 184 0.116 711 0.220

Caryophyllaceae 16 0.010 20 0.013 36 0.011

Casuarina 9449 5.743 8874 5.574 18323 5.660 2

Chenopodiaceae 1348 0.819 970 0.609 2318 0.716

Cyperaceae 124 0.075 91 0.057 215 0.066

Elaeocarpaceae 16 0.010 43 0.027 59 0.018

Bischoffia 2147 1.305 1040 0.653 3187 0.984 10

Macaranga 2599 1.580 776 0.487 3375 1.042 9

Mallotus 3038 1.846 649 0.408 3687 1.139 8

other Euphorbiaceae 415 0.252 1008 0.633 1423 0.440

Fagaceae 537 0.326 1362 0.856 1899 0.587

Liquidambar 2121 1.289 624 0.392 2745 0.848

Lauraceae 1211 0.736 244 0.153 1455 0.449

Mimosa 454 0.276 1599 1.004 2053 0.634

other Leguminosae 845 0.514 535 0.336 1380 0.426

Liliaceae 28 0.017 70 0.044 98 0.030

Magnoliaceae 220 0.134 128 0.080 348 0.107

Broussonetia 103989 63.199 112358 70.575 216347 66.826 1

Humulus 4135 2.513 4837 3.038 8972 2.771 5

Morus 2228 1.354 2251 1.414 4479 1.383 7

Myrsinaceae 40 0.024 144 0.090 184 0.057

Eucalyptus 535 0.325 114 0.072 649 0.200

Melaleuca 591 0.359 341 0.214 932 0.288

Syzygium 78 0.047 587 0.369 665 0.205

Oleaceae 112 0.068 68 0.043 180 0.056

Palmae 914 0.555 443 0.278 1357 0.419

Poaceae 7377 4.483 6058 3.805 13435 4.150 4

Rosaceae 90 0.055 16 0.010 106 0.033

Rubiaceae 184 0.112 78 0.049 262 0.081

Salix 209 0.127 68 0.043 277 0.086

Scrophulariaceae 208 0.126 130 0.082 338 0.104

Solanaceae 62 0.038 67 0.042 129 0.040

Eurya 95 0.058 48 0.030 143 0.044

Trema 8540 5.190 7710 4.843 16250 5.019 3

Zelkova 555 0.337 39 0.024 594 0.183

Miscellaneous 195 0.119 522 0.328 717 0.221

Pteridophytes 1210 0.735 503 0.316 1713 0.529

Asplenium 68 0.041 20 0.013 88 0.027

Athyriaceae 12 0.007 63 0.040 75 0.023

Cyatheaceae 865 0.526 146 0.092 1011 0.312

Dryopteridaceae 4 0.002 49 0.031 53 0.016

Gleicheniaceae 60 0.036 68 0.043 128 0.040

Lycopodiaceae 12 0.007 22 0.014 34 0.011

Nephrolepis 47 0.029 8 0.005 55 0.017

Polypodiaceae 8 0.005 28 0.018 36 0.011

Pteridaceae 32 0.019 16 0.010 48 0.015

Miscellaneous 102 0.062 83 0.052 185 0.057

Sum 164541 100.000 159204 100.000 323745 100.000

Botanical Bulletin of Academia Sinica, Vol. 38, 1997

of the total in a recent study in the Taipei area (northernmost Taiwan) (Peng, 1994) and 66.83% in the present study in the Western Coastal Plain, but it had never assumed an appreciable importance in earlier reports. In the present study from late March to mid April in both years, the daily mean of Broussonetia ordinarily varied between 200 to 550 grains/m³ on dry days, and reached a high of 607 grains/m³ on 3 April 1994. Its daily quantity in the air was much influenced by two meteorological factors: precipitation and temperature. As shown in Figure 5, the pollen curvature of March_April 1995 is much wavier and sharper and with higher peaks than that of 1994. This is intimately correlated with the weather: rain showers were much more frequent and heavier, and the temperature was much less steady in March and April of 1995 than in the same period of 1994. A rain shower always decreased the pollen concentration drastically, and a sharp pollen peak normally appeared following a rain shower (Figure 5). The positive effect of rain as reported by Berggren et al. (1995) that pollen counts increased rapidly concurrently with the beginning of a heavy rain shower was only observed once by us on 8 March 1994.

The dominance of Broussonetia is apparently much related to some superiority of its phenology and pollen features. In Taiwan, Broussonetia papyrifera is common in drier and more open vegetation in wild lowlands as well as in the abandoned land in many metropolitan areas. The mature male plant of this species is usually 4_5 m tall, has a spreading canopy, and produces ample descending male inflorescence at anthesis. Its pollen is spherical to ellipsoid, small (10_12 µm in diameter), thin-walled, and without pollenikitt. In the vicinity of our collection site, there were only a few male plants of B. papyrifera, 300 m to 1,000 m away from the trap.

Figure 2. Important airborne pollen taxa in Taichung, Taiwan, from 1 May 1993 to 30 April 1995.

Figure 3. Pollen calendars of Broussonetia and Casuarina in Taichung in 1994.

Figure 5. Correlation between pollen concentration of Broussonetia and meteorological factors (temperature and precipitation). A, in the 1994 flowering season; B, in 1995.

Figure 4. Pollen calendar of Humulus and Poaceae in Taichung in 1994.

Tsou et al. — Airborne pollen in Taichung, Taiwan

Throughout the year, pollen rain was heaviest in springtime during which Broussonetia, Casuarina, and Trema were major pollen contributors. Summer appeared to be the poorest season in both floristic composition and absolute quantity of the pollen spectrum, Poaceae, Humulus, and Mimosa being the significant members. In fall, pollen concentration rose moderately, due mainly to the increase of grass and Alnus pollen. After fall, the total amount dropped again and grasses, Urticaceae, and Humulus became important contributors.

The present investigation also showed that the airborne pollen spectrum did not reflect the floristic composition in the vicinity of the collection site. A great many individuals from more than 100 families grew naturally or in cultivation in the area within 1-km distance from the collection site. Of them, plants of Palmae (Archontophoenix, Phoenix, Roystonea), Myrtaceae (Eucalyptus, Melaleuca), Apocynaceae (Alstonia), and Moraceae (Ficus) were quantitatively most significant. However, because they were basically zoophilous, none of them proved to be important donors to the airborne pollen assemblage. Among the cultivated plants found around the collection site, only Casuarina, Bischoffia, and Liquidambar were remarkable. Thus, the present investigation illustrated a rather common incongruency between plant composition and aeropalynological spectrum in urbanized areas, where zoophilous cultivated plants abound, and on the other hand supported the notion that only anemophilous taxa are of great potential importance to the airborne pollen spectrum, particularly those of the so-called Amentiferae—they produce well-airborne pollen grains in quantity.

Pollen allergy is among the major topics in aeropalynology. Pollen of grasses, birches, alders, ragweeds, Cryptomeria and Chamaecyparis prove to be among the important aeroallergens in Australia, Europe, North America, mainland China, and Japan (Knox, 1979; Johansen, 1992; Galan et al., 1995; Berggren et al., 1995; Ye et al., 1988; Horiuti et al., 1991; Ogasawara et al., 1991); they might do so in some other extra-tropical regions in the world. In Taiwan, a mountainous subtropical island, the pollen spectrum in the air appears much more complicated than that of temperate regions. Grass pollen has been reported as the major component in some earlier aeropalynological investigations (Huang and Chung, 1973; Chen and Huang, 1980; Tsou and Huang, 1982); however, its proportion remained at 20% or so. In contrast, Broussonetia has come out to be predominant (70.37% & 66.83%) in recent studies (Peng, 1994, the present one) while grasses (4.15%) and Compositae (0.93%) were of minor importance. According to the skin tests of pollen allergenicity (Ye et al., 1988), nearly all of the significant pollen taxa (f > 1%) revealed in the present study are allergic. Of them, one finds the five quantitatively most important taxa: Broussonetia, Casuarina equsetifolia, Trema orientalis, Poaceae, and Humulus scandens, constituting 84.43% of the total. In conclusion, further study of these five taxa on the correlation between their individual pol

len concentration and the allergenicity, especially that of Broussonetia papyrifera, appears crucial.

Acknowledgements. We want to extend our appreciation to the National Science Council of the Republic of China for the financial support (grants NSC 83-0409-B-001-001-B08, 84-2311-B-001-010-B08, 85-2311-B-001-001-B14), to Mr. Yen-Liang Lai for maintaining our collection site, and to Dr. Chung-Fu Shen for commenting on the manuscript.

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