OCCURRENCE AND ECOLOGICAL CHARACTERISTICS OF C-4 DICOT AND CYPERACEAESPECIES IN THE HUNGARIAN FLORA

The non-graminaceous wild nora of Hungary was screened for C-4 plants by using the stable carbon isotope ratio, the leaf anatomy and the pho tosynthetic carbon dioxide compensation concentration to determine the photosynthetic pathway type. On the whole, 31 C-4 species (native or naturalized) were found in the Amaranthaceae, Chenopodiaceae, Cyperace ae, Euphorbiaceae, Portulacaceae and Zygophyllaceae families. Together with the 26 C-4 grass species (Poaceae) reported earlier (Kalapos 199 1), a total of 57 wild C-4 species occur in Hungary, which forms 2.6 % of the country's angiosperm flora. This figure is somewhat higher tha n what was expected on climatic grounds, a fact probably due to certai n edaphic conditions favouring C-4 plant growth. In Hungary, the C-4 s pecies are predominantly annuals growing in open habitats such as dry grasslands, inland saline areas, temporarily exposed riverbeds and dis turbed sites. In comparison with C-3 plants, the C-4 species have high er temperature and light preferences, and their phenology lags behind that of the C-3 plants. These differences might account for C-4 plants being usually excluded from productive biotopes in Hungary, where the C-3 canopy may become closed during the growing season before C-4 pla nts can start their ontogenetic development. Ecological properties of C-3 and C-4 plants differ considerably in the Cyperaceae, but much les s in the Chenopodiaceae family. Among C-4 annuals naturalized aliens a re common, most of which colonized Hungary in the last two centuries. Increasing preponderance of C-4 plants is anticipated in the future as a consequence of possible climate changes and the ever increasing hum an impact on terrestrial vegetation.