Microfungal biomass and number of propagules in an andosol

MICROFUNGAL

BIOMASS AND NUMBER IN AN ANDOSOL

OF PROPAGULES

A. T. MARTINFZ and C. RAMIREZ Institute “Jaime Fe&m” de Microhiologia. Investlgaciones Cicntificas. Joaquin Costa (Acwptrrl

Consejo Superior de 32. Madrid-6 Spain.

30 .4pril 1978)

Summarp~The microfungal community of an andosol. under an acid beech forest located in a zone of the Province of Navarra (Spain) characterized by a temperate climate and high rainfall was studied. Mycelial length. numhcr of spores and fungal biomass were estimated hy the agar-film technique. The number of fungal propagules were estimated by plate counting. There was a pronounced decrease of fungal propagules and mycelial biomass with soil depth; the highest values were obtained in the spring and the autumn. Seasonal variations were attenuated with increasing depth. In autumn the leaves of the A,,, horizon contained a great number of fungal spores hut there v+as little mycelial growth. INTRODCICTION

Jagnow (1971), Nag&de Boois and Jansen (1971) and Lindgreen and Jensen (1973) used the agar-film technique to estimate mycelia in beech forest (Fagus sil~)ufica) soils in Germany, Holland and Denmark respectively. In New Zealand. Ruscoe (1971) measured mycelial lengths in a beech forest (Nofh&uyu.s truw cccta) soil using Witkamp’s (1960) technique which gives lower values than the agar-film technique. There have been very few microbiological studies of andosols. Petia-Carbriales and Valdis (1974) counted fungal propagules in an andosol under Ahirs rdigiosa forest. Despite the scarcity of information about these soils. they present a number of characteristics that may have important modifying effects on the microbial community. Schaefer t’r al. (1960) Urbina et a/. (1969 and 1972) and Klenner de Meixner and Schaefer (1972). when studying the ecosystem of andosols under Noth&u+r.s rlornhr)‘i forests, concluded that the slow mineralization of organic matter in these soils was not due to a scarcity of active microorganisms, but rather to a very efficient ccosystern regulation mechanism in which allophane and aluminium. bound to organic matter. played an important part. Moriy6n et al. (1978) carried out a general microbiological analysis of the soil we have studied. They found that the number of bacteria was low in contrast with the high number of fungal propagules. Here we present a quantitative study of the microfungal community in this andosol and its variation during the year and in the whole profile. MATERIAL

tures. Soil studies by lfiiguez and Barragan (1974) showed that the A,, and A, horizons could be differentiated. The latter was divided into several subhorizons (Table 1). The humus was of the mulliform type. The rock was a phyllitc that appeared at 1 m. The soil is a typical Andaquepts (Soil Taxonomy. 1975); Gleyic Andosol (F.A.O. classification, 1968); humipherous andosol of cold climate (French classification), (Classification des Sols. 1967).

The mycofloras of the A,,,, A,, and A,, horizons were studied throughout 1975. In each horizon four different and representative zones were sampled. once per season. The agar-film technique (Jones and Mollison. 1948; Thomas et a/., 1965) was employed for direct estimations. Films were stained with phenolic aniline-blue. Microscopic observations were made with a magnification of 500 x. With this technique. mycelial length. number of spores, fungal biomass, the percent of biomass corresponding to the myelium and the amount of dark-coloured forms among spores and mycelium were estimated. We were not able to calculate live forms. because of the presence of large numbers of pigmented spores and mycclia. Therefore. the phenolic aniline-blue stain technique (Thomas ~‘r ctl.. 1965; Nagel-de Boois and Jensen. 1971) and the phase-contrast microscopic technique (Frankland, 1974. 1975a. 1975b) were not suitable. Consequently Tahlc

I. Soil data

The zone under study is situated on Oroquieta Pass, in the Province of Navarra (Spain). at 800m in altitude. The vegetation is formed by an acid beech forest (F. sihticu). Climatic data have been reported by Liso and Ascaso (1969). Following the climatic classification of Thornwaite, the climate can be described as Perhumid. Mesothcrmic. generally without a deficiency of water and with mild summer tempera-

” DetermIned 529

subhorizons’ A IL

A,, Depth (cm) Bulk densit) (I,, C C/N PH (H,O) Al”+ (mequiv.lOOg.) Amorphous material - Fe,O, -SiOz Al,O,

AND METHODS

for mineral

0 20 0.48 X.26 20.65 3.85 2.1

2@60

3.64 7.2’ 7.30

3.03 7.09 x.9 I

0.53 561 23.1x 4.50 2.7

(“,,):

bq Iiiigucr and Barragin

(1974).

4. T.

530

Table 9. Results length ~alucr XL

MARTIN

/ and C‘. KAMIKI L

obtained by the agar-film technique expressed in g ’ oven-dr! (100C‘) wil. Mycehal expressed in m g-‘. the number of spores In g-l and the total biomass in parts’ IOz of thl: total amount of the soil Winter

A 00

AI I

A IL

Mqcclinl length (m g- ‘) Number of spores (IO”. g-1) Biomass (mg f.w. g-I)*

Autumn

3x0

2 I90

1790

36

12s

xx

x3

4x.4

21.3

62.X

SXO

300

Mycelial length (m g I) Number of spores (IO”. g I) Biomass (mg f.u. pm ‘)*

Summcr

8X0

22.7

Mycehal length (m g ‘) Number of spores (lO”.g-‘) Biomass (mg f.w. g- ‘)*

* Biomass

Sprmg

450

x70

5.1

17.0

IO.4

16.4

6.4

13.8

IO.4

I x.2

56

69

124

I ox

I.5

I .o

I.2

3.4

2.6

I.2

I.6

2.6

values are expressed on a fresh weight basis.

the biomass values indicated correspond to live and dead forms. Sections of soil embedded in methyl metacrylate (prepared by the Department of Soil Science. University of Navarra). were also examined. We assumed an average fungal density of I .Sg ml ‘. according to Parkinson elf ul. (1971) and Frankland (1975a). to calculate fungal biomass from mycclial length values and number of spores. We determined that the average diameter of hyphae and sports were 4 and 6,um respectively. The biomass values arc expressed on 21 fresh weight basis. The medium used for viable propagulc counting W;IS a glucose (2”;,). yeast extract (0.5”,,), agar (2”;) plus O.Ol”,, oxytetracycline chlorhydrate (pH 6.6). The medium was inoculated on the agar surface and incubated 8 days at 27’C. The significance of determinations was calculated by the variance analysis test applied to the logarithms of data. accepting a significance level of 5” ,I RESULTS

Our results are shown in Tables 2 and 3. All variations of mycelial length. the number of spores. the fungal biomass and the number of propagules down the profile. were statistically significant, except for biomass between A,,, and A,, in autumn and the propagule number between A,, and A,, in winter and summer. The annual variations were less important and without significance in many cases. We have to keep in mind that seasonal values were less repre-

sentative than those of horizons. Seasonal variations diminished with depth. Higher values corresponded to spring and autumn. except for mycclial lengths in A 00, which were very low in the autumn. Mycelium ~21s the largest proportion of the biomass that became dominant with depth. Nevertheless. except for the low proportion of mycclium in A,, in autumn. these did not represent statistically significant changes. Comparing the relative importance of hyaline and dark forms we found_ that the latter corresponded to 75”,, of spores atid to So”,, of mycelium length and that its variation along the profile W;IS very small. Mycelial lengths and spore numbers wcrc calculated from soil sections corresponding to A,, and A ,2 subhorizons during the summer. Comparing these results with those obtained with the agar-film technique. mycelial length values were very similar. while spore number values from soil sections were quite low.

The values representing mycelial length and number of spores were very high. Comparing our results with those found in similar studies carried out on beech forest soils, only values found by Nagel-de Boois and Jansen (1971) were as high as those we recorded. Frankland (1975a). studying a mixed wood composed of QIKKYIS. Brrulu and Fruuirlw found mycelial biomass values close to our own. On the other hand. Parkinson et ul. (1968) found very Ioh mycelial lengths in a Pirllr,\ forest soil.

Table 3. Numbers of fungal propagulcs obtained by soil dilution plate counting (IO“. g-l). Results are expressed in g-’ oven-dry (100 C) soil

Winter A 00 A 11 A IL

24.5 2.4 2.4

Spring 2 13.0 I I.3 2.4

Summer

Autumn

23.5 2.2 1.1

39.0 7.9 0.6

Microfungal

The coincidence of mycelial length values either from soil sections or from soil agar-films is rcmarkable. The low spore number obtained in soil sections is probably because they are easily masked. As has been found by others both biomass and number of spores estimated by direct counting and number of propagules obtained b> plate counts diminished significantI! with soil depth. Ml;cclium length showed the same variations with the exception of autumn. During this season the reccntlq-fallen leaves on the A,, horizon had not been colonised by fungal mycelia. The spring was the season which presented 21 higher degree of leaf colonisation. As found b! Jagnow (1971) and Ruscoe (1971). the values in the present soil were highest in spring and autumn. except for the low values of mycelium in horizon A,, in autumn. With the exception of A,, horizon during autumn, the higher values of biomass corresponded to those of the m)celium. We think that its increase with depth could be related with a diminution of sporulation with the lowering of Oz tension. The

high

proportion

of dark

forms

found

bj

us

could be due to higher resistance to degradation and furthermore to that. even when the phenolic anilineblue stain wxs used in microscopical observation. the hyaline forms could be underestimated. Anqwn.\. the high

absolute

values

of pigmented

think of their possible of humic compounds very abundant in these tent of organic matter

forms

led

us to

participation in the formation (Haider c’t cl/.. 1975). that are kind of soils. with a high conand a rapid humification.

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biomass in an andosol

de Edologic.

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