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Relationship between airborne fungalspore presence and weather variables:Cladosporium and AlternariaMervi Hjelmroos aa Palynological Laboratory , Swedish Museum of Natural History ,Roslagsvägen 101, S-104 05, Stockholm, SwedenPublished online: 01 Sep 2009.

To cite this article: Mervi Hjelmroos (1993) Relationship between airborne fungal spore presence and weathervariables: Cladosporium and Alternaria, Grana, 32:1, 40-47, DOI: 10.1080/00173139309436418

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Grana 32: 4047, 1993

Relationship between airborne fungal spore presence and weather variables Cladosporium and Alternaria

MERVI HJELMROOS

Hjelmroos, hl. 1993. Relationship between airborne fungal spore presence and weather variables. Cladosporiirrri and Alterriaria. - Grana 32: 4047. ISSN 0017-3134.

By means of regression analysis the Clodosporiiinr and Alterriaria spore counts for 19SGS9 for Stockholm are explored and modelled at &hour intervals in order to find the relationship betwen spore presence and climate for the same time periods. Six different weather parameters are uscd. For Cladosporiurn daily mean temperature and daily precipitation secm to be consistently signif- icant. The presence of Alterriaria appears to be more complex. There is a tendency for Alterrimia spore concentrations to increase with the daily precipitation, wind vclocity and total cloud cover. The models are evaluated statistically. On the basis of 10 years of data from roof level in Stockholm the natural background load of Cladosporiirni and Alterriaria as the most prevalent fungal aeroallergens is presented and discusscd. hlervi Hjefntroos, Palyttological Laboratory, Swedish hliiseritn of Natrrral History, Roslagsrr?gei 101. S-103 0.5 Stockliolm, Sweden. (hlariiucripr received 30 April 1992; revired version accepted 4 October 1992)

Cladosporiirm spores is reported to form majority of air- borne spores in the temperate zones (Davies 1969, Solo- mon 1978). Cladosporiiitii species live, like those of AI- tertinrin as saprophytes or as parasites on many kinds of plants. Alterrinrin also has a world-wide distribution. Moulds are common aeroallcrgcns and both Cladosporiiitu and Altcrtinrin are considered to be,the more prevalent of these aeroallergens (Vijay et al. 1991, Budd 1986).

Within plant pathology numerous efforts have been made to find models for the spore dispersal of plant patho- genic fungi (McCartney 1991 and lilt. cited). Sporulation and spore dispersal depend on biological, climatic and physical processes. McCartney (1991) states that the dis- persal of fungal pathogens is mostly determined by physical constraints with wind and rain as the most important carri- ers in space. However, since the point source for the air- borne fungus spores is normally unknown, the models ap- plied to the dispersal of plantpathogenic fungi cannot be used for spores collected at roof level. The aim of this investigation was to find, on the basis of

10 years of data, whether any relationship could be found between the presence of Cladosporiirni and Altertinria and weather variables, by statistically modelling the spore counts in relation to a variety of climatic parameters. The models are statistically evaluated in order to determine which weather variables contribute most to the spore con- ccntrations or responses and which climatic, variables ap- pear to be unimportant. In addition the Cladosporiirrii and Alterriorin spore concentrations in Stockholm, Sweden, during the period 198G89, are discussed.

MATERIAL AND METHODS

Spore sampling Atmospheric spores of Cladosporimi and Alterriaria were col-

Fig. 1. Alap showing the location of trapping site (0).

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Airborm firrignl spores nrid wenther 11

spores were counted at a magnification of ~ 4 0 0 . Four fields of 50 pm2, evcntly spaced four mm apart. were counted on each of the 12 transverse strips, corresponding the exposure for every second hour. The counts were converted to represent the average number of spores m-' air using the following equation:

total exposed tape area

(no. of total fields) air intake (field area) ) .x (..,::;r) ~( , For this invcstigation the average values of Clndosporiwn and

Alrerrinrin for 6-hour intervals m-3 over the period June-August are used. Daily averages are calculated by summing the averaged 2-hour mean spore concentration values.

Weather data The weather data is collected at a station run by the Swedish hieteorological and Hydrological Institute. Observatory. The weather station is located ca. 600 m from the pollen trap and situated at the same elevation (44 m above sea level) as the trap.

The weather parameters are available at 6-hour intervals for the same time periods as the fungal sporc counts. A total of six parameters were selected for this investigation. viz. air pressure. wind direction, wind velocity, daily mean temperature. prccip- itation and total cloudiness. The dew-point temperature is used to count the relative humidity (RH). The wcathcr data for the first recording period ( 1 9 S W ) contained many niissing values of the dewv-point temperature and this could not be used in the investiga- tion. However, comparing the data between the relative humidity for the period when the dewv-point temperature is available. and the total cloudiness for the same period, the total cloudiness seems normally to be high when the relative humidity in the air of Stockholm is hiah. Accordinalv. in this investigation a parallel is

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

...:..;.l.T.'..:-. :.; .l.'..:..j.i.l..:..:..;.j.~.'.. : . . ; . ; *~* . : * . : . . j . i .~ . ' . . : . . .

..~.:.:.:.:-.:.:.:.:.~..~.:.:.:.~.~.:.:.:.:.:-.:.:.:*~*~.:.;.:.~.:-..

Fig. 2. Daily average tcmpcrature in Stockholm, June-August 1980-89.

lected over the period 1980-89 using a Burkard Seven Day Volu- metric Spore Trap (modified Hirst spore trap [1952], Burkard Manufacturing Co.) with a flow rate of 10 I minute-'. The trap was placed 20 m above ground level on the roof of the Department of Physics. University of Stockholm (for practical sampling details, see Ogden et al. 1974). The physical features of the area are thoroughly described by Atkinsson & Larsson (1990) (Fig. 1).

The tape (polyester hlelinex film) was placed on the rotating drum of the trap and was coated with a mixture of vaseline and parafin wax in toluene. The drum rotates at 2 mm per hour and the exposed tape for one day is accordingly 48 mm long (the tape width 19 mm). The daily exposed tape was mounted on a slide with Gelvatol (1980-85) or glycerin jelly (1985-89) and the fungal

drawn between The relative k h d i t y and the t&l clouihess. All data, both spore and climate, were omitted for any sampling period with one or more missing climatic variables.

Statistical analysis The numerical approach adopted is that of regression analysis. Regression analysis was used to explore and model the relatioships between organisms and their environment based on observations of the spores presences or abundances in a series of spatial or temporal samples. The data for each taxon are analysed sep- arately. Each regression focuses on a particular taxon and on how that taxon is related to the environmental variables. In the termi- nology of regression analysis. the taxon abundance is the rcsponsc variable and the environmental variables are explanatory or pre- dictor variables. Regression analysis attempts to model the re- sponse variable as a function of one or more predictor variables.

The multiple least-squares regression model is used where E(y) = b, + b,x, + bzx2 ... where E(y) is the expected response of the variable y.

x, and xz are explanatory variables, and b,, b, and b2 are parameters or regression or canonical coeffi- cients.

bo is the expected response when x, = 0 and x2 = 0. b, and b2 are the rates of change in the expected response along the x, and x2 gradients, respectively. b, thus measures the change in E(y) with x, for a fixed value of x2, and bz the change in E(y) with x2 for a fixed value of x,. Standard errors of the estimates for bu. b, and b2 can be calculated along with associated t-values. The t-values can be used to test whether a coefficient is zero, i.e., whether the correspond- ing explanatory variable contributes to the fit of the model in

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42 Hjelniroos, At.

g .............................................. 8 .............................................. 7 .............................................. '"I 6 ..............................................

~ ~~~~~~ ~~~

I U

g .............................................. 8 .............................................. 7 .............................................. 6 .............................................. 5 .............................................. 4 .......................................... 3 ......................................... 2 ....................................... 1 ...................................... 0

Fig. 3. Daily average precipitation in Stockholm, June-August, 1980-89.

I

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addition to the fit already provided by the other explanatory variable(s).

Because the spore concentrations have many zero values and also very high values. they show a strongly skewed distribution. All concentrations were thus transformed to log e(y + 1). The regres- sion were fitted by means of redundancy analysis with only one taxon as the "species data" and with six climatic variables as "environmental data" using the computer program CANOCO 3.10 (Ter Braak 1987, Jongman et al. 1987). The percent variance of the spore data explained for each year by the model was calculated, along with the correlation between the spore and climatic data. The overall significance of each model (taxon and year) was as- sessed by means of htonte Carlo permutation tests. In this case a

restricted pcrmutation test was uscd bccausc the data are from time-series. 99 pcrmutations were completed for each model and the overall significance of the model evaluated. For these tests to be valid, the time series should be trend-free. In all cases the series are stationary, as evaluated by partialling out time as a covariable and regressing the residual spore concentrations on the observed concentrations. No significant time trends were found in the 20 time-series.

RESULTS AND DISCUSSION

The average I0-year data from Stockholm is illustrated month by month with reference to the climatic data in Fig. 2 (average temperature) and Fig. 3 (average precip- itation); the Cladosporiiim counts are presented in Fig. 4 and Alteritaria in Fig. 5. The yearly totals of average daily concentrations of Cladosporiiitit and Altertiaria spores m-3 air (1980-89) in Stockholm are given in Fig. 6.

Cladosporium and Alternaria in the air of Stockholm 1980-89

Cladosporium

Cladosporiiitn is found in the air in Stockholm practically throughout the whole year, with the exception of periods with heavy snow cover (usually January-February). The daily concentration between September and the end of May is low and rarely exceeds 1000 spores m-3 air (Rubulis 1983, Palynological Laboratory, Stockholm: unpubl. data). In the middle of June, when the mean temperature rises above 15°C (Fig. 2), the number of Cladosporiiint spores in the air increases and reaches average values of over 1000 spores m-3 air. Often the daily temperature is high but the the nights are still rather cold and the amount of precip- itation is not high enough to stimulate greater mould growth and spore liberation.

The peak period with spore concentrations between 4000 and 8000 spores m-' air, starts during the second half of July and usually lasts until the middle of August (Fig. 4). At this stage of the Swedish summer, following the high pressure systems of the early summer, thunderstorms and more continuous spells of lowpressures frequently occur. Nights are \vam and the day temperature is normally be- tween 20 and 25°C. It is clear from the 10 years of data that the spore concentration in the air increases greatly shortly before showers. The similar type of increase is seen after the showers, after a 2-4 hour span of time. The temper- ature optimum for the growth of this ubiquitous mould ranges from 18-28°C but growth at -6°C has been reported (Gravesen 1979).

When the daily mean temperature drops below 15"C, in the middle of August, the concentration of Cladosporiiitn spores decreases rapidly by about half (6000 to 3000 spores m-' air). At this time the nights become considerably col- der and temperatures close to 0°C are not uncommon, however, day temperatures can still bc very high.

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Airborrie firrzgnl sporcs nrid irmtlicr 43

temperature on this day was 20.1"C and it raincd 0.9 mm at thc night, bcfore 01.00 AM. The relative humidity during the whole day rangcd betwecn 56 and 77%. The peak concentration of Clndosporiirrii spores occured between 02.00 and 01.00 PM and the concentration was generally very high during the wholc day. Gencrally the highest daily concentration each year ranges from 10 000 to 20 000 spores m-'.

The annual totals for Clndosporiirrri in 1980-89 generally range from ca. 220000 to ca. 300000 (Fig. 6). the yearly totals for Clndosporiiitri sporcs in relation to the total air- borne spore catch in Stockholm is shown in Table I. In 1989 the total of the average daily concentrations reached ca. 450 000, which is more than 30% above the 10-ycar aver- age. In this particular year the peak season started in the beginning of June, over one month earlier than normal. The spring was very dry and warm, in the later part of May daily mean temperatures were above 20°C and the relativc humidity was generally over 50%. Total precipitation for the whole month was only 29.7 mm. In June the tempcr- ature was even higher. it rained 39.1 mm and thc average relative air humidity was 61%; the climatic and biological conditions were optimal for microfungal growth and spor- ulation. In 1987 the peak season was scarcely noticeable. The summer was extremely rainy and cold, the mean tem- peratures for June-August being between 12.4 and 16°C.

The growth, sporulation and dispersal of Clndosporiirrii seems to be very sensitive to changes in the climatic sit- uation. Precipitation itself (Fig. 3) appears to be a limiting factor for Cladosporiitrii sporulation and dispersal, but the daily precipitation in combination with daily mean temper- atures of over 15°C. which gcncrally also produces an in- creased relative humidity, is one of the positive factors contributing to an increased concentration of Clndospo- riirtii in the air. Cladosporium is considcred a membcr of the dry air spora and the discharge of spores is facilitated by dry windy conditions. The concentrations increase sub- stantially, but briefly before the rainfalls as a result of the wash-out. After the rain a certain increase of the concen- trations is observed. This could be result of the increased soil moisture which eventually could stimulate the Cln- dosporiirrii growth leading to increased spore production. The investigated 6-hour intervals are apparently not suffi- ciently short periods to solve the problem.

ma air 3000-:::::::::::::::::::::::::::::::- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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7500 . j . i ..........i.i.:.:.. . . ... .......:....i.i..........i.i..:.......i.i.:.:... . . . . r . i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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sooran m3 ak

s o o q ; : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....... >.........,................. ........................ ;.;.>.; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ALgubf ' ' ' ' ' ' ' 3 1' Aljgiuit

Fig. 4. Avcragc daily concentration of Cludosporiun~. June-Au- gust, 1980-89.

Spore concentrations in the peak season are much higher during the day time than at the night, the daily peak often occurs between 08.00 and noon. The same type of circadian periodicity of Clndosporiiitri has been found in Finland (Rantio-Lehtimaki et al. 1991a, 1991b). The peak in S W Finland seems generally to occur ca. 2 hours later than in Stockholm.

The highest concentration in Stockholm for the 10-year period occurred on 29th July 1986 when the number of spores m-3 air during one day was over 34 800. The mean

Altertiaria

Altertinria common saprophyte throughout the world, is often found growing together with Cladosporititii. Opti- mum growth temperatures range from 22 to 28°C while occurence is very rarcly if the tcmperature falls below 0°C. Altertzarin like Cladosporiirriz occurs in Stockholm more or less frequently throughout the whole year. The daily aver- age concentrations in the peak season are much lower than those of Clndosporititri and it is only sporadicaly found in the air from September to early June. Because of its rela-

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sporqs d air

75- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

sporas ma air -

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . t " ' " " " 1S'ALguit' ' ' ' ' ' ' ' 31 Xliqirat

Fig. 5. Average daily concentration of Alterriaria, June-August, 1980-89.

tively large spore volume (2300 p'; Hyde 1972) Alterriarin is believed to be strongly underrepresented in the spore counts at roof level (in this case 20 m). This could also be one of the reasons why Alterrinrin concentrations seem to be positively influenced by wind velocity.

The peak season in Stockholm is short (Fig. 5). The concentration is usually less than 25 spores m-3 air in June- July. At the end of July Altcrtinrin frequencies increase and the peak usually occurs during the first half of August when the average daily values range from 50 to 70 spores m-3 air. The highest daily average concentration during the period

investigated was counted on 7th August 19S4 (560) when the mean temperature was 18°C. The night (00.00-07.00) was extremely foggy and there was slight rain every now and then (0.4 mm). The relative humidity was generally over 72% during the whole day. Alteriinrin spores occured between 04.00 AM and 02.00 PM with a peak around OS.00 AM.

Usually, the highest daily average during the peak season is around 300 spores m-3 air.

In Denmark, in a 10-year collection of viable spores at roof level, the Alterrinrin frequencies show the same pat- tern as in Stockholm (Larsen 6: Gravesen 1991). The high- est number of Alterrinrin colonies were usually encounted in August and the number of colony forming units m-3 was of the same size as the spore catch on the tape in Stock- holm. This could mean, since the trends atributed are simi- lar, that the majority of the AIterrinrin spores in the air are still viable even when trapped by different methods.

The yearly totals of average daily concentrations for Alterriarin normally range from ca. 1000 to slightly over 2000 spores In 1989 climatic and biological conditions were extremely favourable for Alterrinrin growth, spor- ulation and dispersal (cf. Clndosporiiim). The yearly total of average daily counts was over 4200 spores m-' which is ca. 50% higher than the 10-year average. The cold and rainy year, 1987, similarly restrained Alterrinrin growth and, in this year, a total of only 832 Alteriiarin spores m-3 were recorded. The comparision betwee'n the annual Al- terrinrin spore counts and the total number of all analysed airborne spores in the air of Stockholm is shown in Table I.

In addition to changes in temperature and precipitation, Altertinrin seems to be rather sensitive to variations in relative humidity and cloudiness. Altertinrin is, like Cln- dosporiirrti, considered member of the dry airspora and favoured by relatively strong winds. For the years in ques- tion in Stockholm, as a rule, if the relative humidity rises above 45%. total cloudiness is over 60% and the winds are rather strong Alterriaria concentrations increase. On the other hand, when total cloudiness is less than 40°/0, which generally means a lower relative humidity Altertinrin con- centrations decrease. The increase of concentrations before the rain are not so significant as the increase of Clndospo- riirrn spores. The increase after the showers is more pro- nounced, but even in this case the 6-hour intervals are too long to explane the relationship: rainfall - edaphic factors - increased spore production.

Statistical analysis

Cladosporiirtti

Of the 10 years, all the models are significant at the 95% level except for 1980. The significant models account for 9.4-35.2% of the total variance in the Clndosporiirni con- centrations. Although different climatic variables have sig- nificant canonical coefficients, as assessed by their associ-

Graria 32 (1993)

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Airboriie fiiiignl spores arid Irvntlier 45

Fig. 6 . Yearly totals of average daily concentrations of Clndosporiitrn (A) and Alterrinrin (B).

ated t-values (shown by * in Table 11), two climatic varia- bles are consistently significant for nearly all years, namely daily mean temperature and precipitation. Both have posi- tive canonical coeffients, implying that when they increase, the response variable Chdosporiiitti, also increases. A gen- eral model, based on the significant 1981-1989 models would be of the form:

E (loge Clndosporiirtii + 1) = 0.613 x, + 0 . 5 0 2 ~ ~ (1)

whcre x, = daily mean temperature for a 6-hour period x2 = precipitation for a 6-hour period.

Alrertinrin

None of the models for the 10 years is significant at the 95% level and none of the six climatic variables have signif- icant canonical coefficients. The models explain 1.0-18.0% of the spore data and have correlations ranging from 0. 10 to 0.46 (Table 111). No statistical model can be proposed for Allerrinria spore concentrations in relation to climate.

Table I. The proportion of the atitiual Cladosporiiirii ntid Altertiaria spore coiitits of the yearly total of airborne jhigal spores iii rhe air of Stockholm (1980-1989).

Year Cladosporiunt Altertiaria Total (spores rn-’ air)

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 -

146.296 221.600 282.300 272.400 275.540 247.836 351.328 94.588

191.594 418.340

677 1.520 1.660 2.340 2.780 1.934 1.976

832 1.118 4.238

506.948 462.640 488.740 527.440 814.200 778.208 823.316 697.358 510.198 603.772

There is a tendency for Altertinrin spore concentrations, at a higtht of 20 meters, to increase with precipitation, and, in part, with wind velocity and total cloud cover. A general, qualitative model would .thus be of the form:

E (loge Alterrinrin + 1) f(xJ + (x2) + (x3) (2)

where x, = precipitation for a 6-hour period x2 = wind velocity for a 6-hour period x3 = total cloud cover for a 6-hour period.

CONCLUSIONS

The presentation of the 10-year spore data for the air Stockholm demonstrates the natural background load of Clndosporiiwt and Alteriinrio, their seasonal and circadian variation, the average daily values and the relation to cer- tain weather parameters.

The investigation period of 10 years is too short a time to demonstrate any long-term fluctuations in the total Cln- dosporiiitti and Abertiarin presence in the air of Stockholm at roof level (Fig. 6). That must be largely dependent on long-term climatic fluctuations. Both mould species are clearly dependent on the daily precipitation and even short showers can drastically change the concentrations if the other climatic parameters, such as temperature, are opti- mal. The concentrations increase briefly before the show- ers, this wash-out is more pronounced in Clndosporiiim than in Altertanria. The increase of atmospheric concentra- tions after the rainfall is generally longlasting with the peak some hours after the rain. Because the weather parameters are available at 6-hour intervals, the information of shorter periods is difficult to interpret. Since the total cloud cover, together with precipitation and wind velocity, is one of the possible variables for Altertlaria a positive correlation with relative humidity (RH) could also be possible. Rantio- Lehtim5ki et al. (1985) found that correlations between relative humidity and airspora were exclusively negative. In those correlation analyses daily mean values were used. In the present study 6-hour mean values are used and the results are thought to be more significant. although even

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46 Hjelriiroos, M.

Table 11. Cl~dosporiiit~i spore coricetilratiotis (log y + I ) , 198049. * = Significant at u = 0.05 (5% significance level).

1980 1981 1982 1983 1983 1985 1986 1987 19S8 1989 Sum Significance

Percentage varianceexplaincd 10.4 35.2 16.1 23.2 38.3 33.3 27.8 9.4 28.4 25.1 Spore-climate correlation 0.32 0.59 0.40 0.48 0.62 0.58 0.53 0.31 0.53 0.25

Canonical coefficients Air pressure -0.245 -0.028 -0.523 -0.398 0.760 0.032 -0.349 -0.165 -0.191 -0.586 Wind direction 0.381 0.245 0.240 -0.067 0.191 0.374 0.093 0.198 0.087 -0.062 Wind velocity 0.050 -0.204 0.016 -0.054 -0.046 0.012 -0.064 -0.065 0.013 0.141 Daily mean temperature 0.880 0.662 0.364 0.726 0.771 0.538 0.540 0.664 0.690 0.562 Precipitation 0.253 0.452 0.715 0.311 0.337 0.612 0.625 0.522 0.561 0.382 Total cloudiness 0.022 0.044 -0.266 -0.156 0.085 0.112 -0.187 -0.103 -0.254 -0.184

1-values of coefficients Air pressure -1.44 -0.32 -3.60' -3.18. 0.94 0.36 -3.32* -0.84 -1.95 -5.50; 4 Wind direction 2.36. 3.07* 1.91 -0.60 2.65. 4.56' 0.97 1.09 0.96 0.64 4 Wind velocity -0.31 -2.43' 0.12 -0.48 -0.59 0.15 -0.64 -0.33 0.14 1.43 1 Daily mean temperature 4.46* 6.66' 2.09* 5.46' 7.24* 5.14' 4.08. 2.85' 6.95' 4.91' 10 Precipitation 1.41 4.55* 4.47' 2-16. 3.50 5.80' 5.02* 2.15* 5.33* 3.34* 8 Total cloudiness 0.12 0.47 -1.51 1.21 0.97 1.28 -1.66 -0.49 -2.41' -1.62 I

Number of samples 365 366 366 364 355 364 364 366 366 361

Significance (p) of model 0.12 0.01' 0.02* 0.01' 0.01' 0.01' 0.01. 0.05' 0.01' 0.01* 9

Variable with highest t-value Daily Daily Precipit Daily Daily Prccipit Prccipit Daily Daily Daily mean mean mean mean mean mean mean temp. temp. temp. temp. temp. temp. temp.

Table 111. Altertinria spore coticetitrntiotts (log y + 1). 1980-89.

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 Sum

+ - Percentage variance explained 7.5 21.2 2.7 1.0 9.8 10.3 17.3 18.0 4.3 8.3

Spore-climate correlation Canonical coefficients

Air pressure Wind direction Wind velocity Daily mean temperature Precipitation Total cloudiness

t-values of coefficients Air pressure Wind direction Wind velocity Daily mean temperature Precipitation Total cloudiness

Number of samples Significance (p) of model Variable with highest I-value

0.27 0.46 0.17 0.10 0.31 0.32 0.42 0.42 0.21 0.29

-0.651 0.222 -0.605 -0.51 0.799 0.609 0.42 -0.350 -0.099 0.070 5 5 -0.250 0.237 -0.537 0.26 0.376 -0.303 0.69 -0.313 -0.597 0.060 5 5 -0.652 0.553 0.152 -0.73 0.629 -0.140 0.22 0.572 0.117 0.144 7 3

0.216 -0.174 0.567 1.07 -0.165 -0.603 -0.13 0.350 -0.409 0.547 5 5 0.572 0.632 -0.590 -0.83 0.658 0.720 1.07 0.719 0.613 0.442 8 2

-0.391 0.673 -0.553 0.42 0.292 0.011 -0.24 0.366 -0.085 0.548 6 4

-0.613 0.70 -0.269 0.72 -0.679 1.62

0.199 -0.39 0.506 1.38 0.320 1.89

365 366

0.99 0.09

Wind Total velocity cloud

-0.707 -0.264 -0.620 0.158

0.167 -0.406 0.504 0.628

-0.528 -0.397 -0.607 0.247

366 364

0.98 0.99

Air Daily pressure mean

temp.

1.38 1.27 1.03 0.76 -0.66 1.72 1.14 -0.31 0.52

-0.28 -1.19 -0.24 1.01 1.22 1.86 0.57 0.08 -0.58

355 364 364

0.66 0.21 0.19

Air Air Precipt pressure pressure

-0.507 -0.099 0.15 5 5 -0.459 -0.648 0.13 5 5

0.746 0.124 0.33 7 3 0.511 -0.450 0.67 5 5 0.725 0.629 0.88 8 2 0.515 -0.083 1.12 7 3

366 366 361

0.65 0.99 0.62

. Wind Wind Total velocity direction cloud

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shorter time intervals for this type of investigation is needed. Moreover, if the relationships between a combina- tion of several climatic parameters and spore presence are tested for the same time periods, the results can be com- pletely different from testing individual parameters against one other. Daily mean temperatures of more than 15°C when combined with a sufficient amount of precipitation seem to optimize the sporulation conditions for Cladospo- riirm. A delimitation of the favourable conditions for AI- terrtnrin sporulation and dispersal appears to be more com- plex and needs more detailed studies, as well the interac- tion between edaphic factors, actual weather parameters and spore concentrations needs more’detailed studies.

ACKNOWLEDGEMENTS I wish to record my special thanks to Prof. J. Birks who did the statistical analysis and to hlr. K.-A. Larsson who modified the spore and climatic data files so that the records could be used for this investigation. The spore counts for 19SW5 were performed by hlr. J. Rubulis and for 1986 by hlr. K. Hendin. Dr. S. Hicks has revised the English of the manuscript. To all of these I cxpress my gratitude. Financial support from the Stockholm County Coun- cil is gratefully acknowledged.

REFERENCES Atkinson H. & Larsson K.-A. 1990. A l0-year record of the

arboreal airborne pollen in Stockholm, Sweden. - Grana 29: 229-237.

Budd, T. W. 1986. Allergens of Alterriaria. - Grana 25: 147-151. Davies, R. R. 1969. Spore concentrations in the atmosphere at

Ahmadi, a new town in Kuwait. - J. Gen. Microbiol. 55: 425432.

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