Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 77. (Budapest 1985)

P. Komáromy, Zs.: The role of algal synusia of grasslands in successional process in Hungary

of light intensity and their minimum coincided with 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 biomass 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 diatoms 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. In consequence of low productivity, macro- and microclimatic conditions, lack of water, the succession can not progress and stops at open grassland community level with 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. If 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.