ANNALES HISTORICO-NATURALES MUSEI NATIONALIS HUNGARICI Tomus 77. Budapest, 1985 p. 97-102.

The role of algal synusia of grasslands in successional processes in Hungary

by Zs. P. K O M Á R O M Y , Budapest

Abstract—The algal flora of the Hungarian grasslands was studied. The importance of crypto-gamic crusts is well-known, but the studies of floristical patterns of algal communities are rare. Algological investigations on various soil types suggest that algal crusts have characteristic florist­ical composition and take a definite place in the biotic succession of grassy plant communities. With 4 figures.

Grasslands are widespread in the Great Hungarian Plain in consequence of climatic and ed-aphic conditions. The soils of cultivated and uncultivated fields are exposed to erosive impacts be­cause of the lack of woody vegetation. Owing to the low amount of precipitation (ranging between 500-600 mm per year) and the low relief energy, the importance of rainfall erosion is not consider­able. On the other hand, winds devastate freely in the extensive open areas, mainly during the long dry periods.

The grassy vegetation is characterized not only by the lack of woods but by extensive algal crusts as well. The visible algal coats are rich in species but sometimes they are the mass-production of one or two species only.

The cryptogamic crusts are widespread throughout the world in arid zones (ALI & SANDHU 1972, BROTHERSON & RUSHFORTH 1983, CAMERON 1964, DEASON & BOLD 1960, D U R R E L L 1959, FLECHTER & MARTIN 1948). The algal crusts are also the primary components of grassy plant com­munities in Hungary and they play an important role in binding the soil particles and in decreasing the degree of soil erosion.

Filamentous blue-green and green algae of mucilaginous sheaths produce a stable surface layer with soil particles. Having a characteristic microrelief, this layer deflects the micropattern of the wind and decreases the intensity of rain and hence the degree of soil erosion. The algal crusts promote occupation by mosses and lichens and so contribute to the progress of the successional processes. Therefore it is not without interest to have exact information about the species pattern, successional and other relations of the algal synusia of grassy plant communities under semiarid conditions.

The salt-affected soils and calcareous sandy soils of the Great Hungarian Plain are charac­terized by filamentous green and blue-green algae : Chlorhormidium crenulatum, Phormidium, Lyng-bya, Nostoc, Calothrix and other species. They have mucilaginous sheaths and form a compact network with soil particles. This rather firm thin layer offers resistence to mechanical effects in dry and wet conditions.

Algological investigations on solonetz soils in the "Hortobágy" and on solonchak and solon-chak-solonetz and calcareous sandy soils in the "Kiskunság" suggest that these algal crusts have characteristic floristical composition, they are synusia and take a definite place in the biotic succes­sion of grassy plant communities.

Biotic succession is the chronological succession of the plant communities under constant macroclimatic conditions, which happens as a result of either extrinsic ecological factors or by population dynamical processes. The successional processes themselves are realized through a series of coenostates. A coenostate can be considered as a species assemblage existing in a given place and at a given time under a given ecological circumstance. The various coenostates existing side by side in space may be considered as temporal successional stadia.

In the case of salt-affected soils, the alternation of the particulate microrelief, the dry and wet biotopes eventuate the mosaic-like pattern of the small alkali flats, halophyte steppe patches and small astatic salt pools. Al l of the halophyte plant communities provide favourable conditions for the formation of algal crusts. These surface crusts may be rich in species or they are the mass-production of some species.

7 Természettudományi Múzeum Évkönyve 1985

g r a s s - s t e p p e

a lka l i flat zone

Fig. 1. The occurrence of algal species in the quadrat on solonetz soil

Samples from the soil algal synusia were obtained from 5 X 5 m quadrats, consisted of twentyfive 1 m square quadrats. Samples were taken from the alkali flats, halophyte grass communities and from the transitional zone between the two. Four or six algal species occurred in the samples of open grass communities (Artemisio-Festucetum pseudovinae). A great variability of the species was observed i n the alkali flats (Puccinellietum limosae or Camphorosmetum attnuae community). Empty quadrats alternated wi th samples con­taining rich algal flora (8-10 species) as a consequence of the different water conditions of the sampled micro-areas. The soils of the grassy communities, situated on higher ground, possess good water conditions, while the alkali flats are flooded with water in spring. During summer the higher areas gradually dry up, but there are wet patches on the alkali flats wi th enough water for the algae. The other places are absolutely dry. I t is evident, that species richness is the highest i n the places of favourable water conditions of longer periods (Fig. 1).

The algal crusts also exist in dry conditions so the binding soil particles are protected by them from the heavy summer rains and persistent winds. I n addition, they contribute to the succession by the settlement of mosses, lichens and flowering plants in the algal crusts. Erosion is therefore even less. T h e m o s t f r e q u e n t s o i l b i n d i n g a l g a l s p e c i e s w e r e o n a l k a l i s o i l s i n H u n g a r y : Phormidium foveolarum, Phormidium paulsenianum, Calothrix elenkinii, Nostoc commune, Phormidium papyraceum and Lyngbya mucicola (in decreasing order of frequency).

Various zones of plant communities occurred on the shores of the astatic salt lakes. More than a hundred algal species were identified from the examined saline waters (Kiss 1975). A t the margin of saline water the species number decreased rapidly ( K O M Á R O M Y 1980), the characteristic plankton species disappeared and some blue-green algae and diatoms occurred. The species composition of the soil algal synusia and the percentage of various algal phyla is apparently constant in the wet mud (Fig. 2). But the spatial pattern

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astat ic sa l t wet transi t ional g r a s s - s t e p p e l ake mud z o n e

Fig. 2. Change in species number and the percentage of algal phyla on the shore of an astatic salt lake (solonchak soil)

of the algal populations changes in the different zones. A t the margin of the saline water coccoid blue-green algae were found: Chroococcus minor, Ch. paliidus, Ch. turgidus and various diatoms as Amphora coffeiformis, Cymbella affinis, Eunotia veneris, Gomphonema ventricosum, Nitzschia inconspicua and Pinnularia intermedia. The Aster-Plantago zone and the grass steppe communities were characterized by filamentous species: Calothrix braunii, Lyngbya martensiana, Microcoleus paludosus, Nostoc commune, Phormidium angustissimum, Ph. ambiguum, Ph. autumnale, Ph. foveolarum and Ph. papyraceum. The soil algae occupy the places in which flowering plants can not exist because of the rapid changes of water conditions. Successional processes take place inside the algal synusia.

Grass-steppe communities (Festucetum vaginatae danubiale) can also be found on the top and the side of sandhills, where the underground water level is deep and the habitat is extremely dry. Communities with Juniperus communis and/or Populus alba (Junipero-Populetum albae) possess some more favourable conditions.

Seasonality and successional processes of soil algal synusia were examined on a sand­hill-side wi th Festucetum vaginatae danubiale community along a 20-meter transect; soil samples were taken at every 1 meter. The top of the sandhill was covered wi th Festucetum vaginatae Stipetosum (for about half of the transect) and Festucetum vaginatae Fumanetosum occurred on the side. A i r vapour content, air temperature, light intensity, and soil moisture conditions were measured in every case. Leaving seasonality out of consideration, the mentioned ecological factors have a mosaic-like pattern. Species number was high in every sample but i t was modest at 8-10 meters where mosses and lichens were dominant among the flowering plants. The percentage of Cyanophyta was high in every sample (Fig. 3).

Both the number of species and the number of specimens was the highest between 11-20 meters, where the cover of flowering plants, mosses and lichens were the lowest. The result o f the three years long examination suggest that algal synusia both in the Fumane­tosum and in the Stipetosum show—beside seasonal changes—successional changes as well .

s p e c i e s -number

30-t V 74% V 84% V t 25 ° C t 25 ° C t 1 12,000 Lux 1 11,400 Lux 1 N 1.9% w 5.7% w

80% 23 ° C 13,000 Lux 5.3%

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V 84% t 26 ° C 1 11,200 Lux w 2.3%

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n a ű U ű n 10 11 12 13 14 15 16 17 18 19 20

Fig. 3. Change in species number and the number of Cyanophyton species along a transect with mosaic-like pattern on calcareous sandy soil. Abbreviations : v = air vapour content, t = tempera­ture, 1 = light intensity, w = soil water content. — Fig. 4. Change in species number and the number

of Cyanophyton species along a gradient on calcareous sandy soil

Decrease in number of algal species and in the percentage of Cyanophyta and the appear­ance of diatoms indicate a higher successional stage of community. Algologically the occu­pation by mosses and lichens also means another successional stage. The soil-binding effects of algal crusts can be pointed out both i n the early and in the late phases of suc­cession.

There may be situations in the Junipero-Populetum albae community when air vapour conditions, air temperature, light intensity and soil water content are found along a gradient. The structure of ecological conditions is reflected by a characteristic structure of the algal synusia. The algological examinations were made along a 20 m transect, where air vapour content and soil moisture content increased, light intensity and air temperature gradually decreased from 0 m to 20 m. A t high light intensity and temperature (coinciding with low air vapour content and dry sand) the percentage of Cyanophyta was high. Where air tem­perature and light intensity were moderate a transitional zone developed wi th high species number because of the appearance of green algae. A t the end of the transect, where Populus alba was dominant, the number of algae decreased and the blue-green algae disappeared. The maximum of individual and species number of Cyanophyta coincided wi th the maximum

of light intensity and their minimum coincided wi th the minimum of light intensity. The maximum of Chlorophyta and Chrysophyta species coincided with the maximum of air vapour content and soil moisture content (Fig. 4).

Grassland communities have low productivity and the quantity of the produced bio-mass is low, total amount of organic matter is small. The origin of minerals is extrabiotic, species diversity is low. Spatial heterogeneity is high but poorly organized and it depends on the heterogeneity of ecological factors. The size of organisms in the community is small, their life cycle usually is short and simple. These characteristics of grasslands can be attrib­uted to climatic and edaphic conditions. On sandy soils, in consequence of present-day macroclimatic consitions, the formed little organic matter is quickly mineralized and can not accumulate enough humus in the soil. Wind and rain erosion is strong, successional processes are slow and sometimes they are slowed down or return to the previous stage. Another factor which impedes the successional processes is the lack of water, and in the case of salt-affected soils edaphic conditions as well.

Under these circumstances soil algal synusia possess great importance in open and closed grassland communities. Algal crusts can be found on extensive bare soils and both seasonal and successional changes can be demonstrated. The changes inside the algal synusia may be short- or long-term. Successional processes were observed on the shores of astatic salt lakes, where independently at season the coccoid blue-green algae and d i ­atoms were succeeded by filamentous blue-green algae both in space and time.

Another case of successional changes was found along a successional gradient (where light intensity, air vapour content, air temperature, soil moisture content changed along a gradient). Cyanophyton species were followed by Chlorophyton and Chrysophyton species, where the light intensity and soil moisture content reached a definite value.

Aspectual changes come into prominence in areas which are determined by mosaic­like microheterogeneity in ecological conditions. By slow successional processes mosses and lichens may settle in the algal crusts and simultaneously decrease the space between the flowering plants. When communities are disturbed (e.g. by grazing, fire etc.), the binding of the soil is decreased and successional processes start again from algal synusia.

Conclusions

1. Algal crusts are widespread not only in the desert areas but also in the open grass-steppe communities, where the macroclimatic conditions are unfavourable for extensive woody plant vegetation.

2. Algal crusts possess special floristical composition, they are important components of the grassland communities so they can be considered algal synusia.

3. The algal synusia usually occupy the extensive bare soil surfaces of exterme ecological conditions and they play an important role in the early phase of successional processes. I n consequence of low productivity, macro- and microclimatic conditions, lack of water, the succession can not progress and stops at open grassland community level wi th algal and/or cryptogamic crusts. The successional processes take place within the algal synusia. Lichenes and mosses are able to displace the algae but these cryptogamic crusts fall victim to degradation so the algae occupy again these new bare patches.

4. I f there is an ecological gradient (e.g. in light, water etc.) the floristical pattern changes along this gradient. Mosaic-like micro-ecological pattern causes mosaic-like floristical pattern. Zonality results in gradient-like changes.

5. The soil algal crusts of grasslands are typical water-limited synusia.

References

A L I , S. & G. R . SANDHU (1972): Blue-green algae of the saline soils of the Punjab. — Oikos 22: 268-272.

BROTHERSON, J . D . & S. R . RUSHFORTH (1983) : Influence of cryptogamic crusts on moisture relation­ships of soils in Navajo National Monument, Arizona. — Great Basin Naturalist 43: 73-78.

CAMERON, R . E. (1964): Algae of Southern Arizona. I I . Algal flora (exclusive of blue-green algae). — Rev. Algol. N. S. 7: 151-177.

DEASON, T. & H. C. BOLD (1960): Phycological studies. I . Exploratory studies of Texas soil algae. — Univ. Texas Publ. No. 6022, Austin.

D U R R E L L , L. W. (1959): Algae in Colorado soils. — Amer. Midi. Naturalist 61: 322-328. FLECHTER, J . E. & W. P. MARTIN (1948): Some effects of algae and molds in the rain-crust of desert

soils. — Ecology 29: 95-100. Kiss, J . (1975): A Fülöpháza környéki szikes tavak mikroflórájának és mikrovegetációjának össze­

hasonlító vizsgálata. (Vergleichende Untersuchungen der Mikroflora und Mikrovegetation der Natrongewasser bei Fülöpháza). — Juhász Gyula Tan. kép. Főisk. Tud. Közlem. p. 3-35.

KOMÁROMY, ZS . (1980): Algae living on the shore of some Hungarian astatic salt lakes. — Annls hist.-nat. Mus. natn. hung. 72: 73-79.

Author's address : fDR. ZSUZSA P. KOMÁROMY Botanical Department Hungarian Natural History Museum Budapest, pf. 222 H-1476