Ecophysiological aspects in 105 plants species of saline and arid environments in Tunisia

In Tunisian arid regions, plant life forms, ecotypes, physiological types and photosynthetic pathways (C 3 , C 4 or CAM) remain unclear. Understanding the characters of these plant species could be important for land restoration. A literature survey was conducted for 105 species from arid regions of Tunisia. These plant species belong to several ecotypes: halophytes, xerophytes, gypsophytes, psamophytes, xero-halophytes, gypso-halophytes, psamo-halophytes, psamo-xerophytes, xero-gypsophytes and hygro-halophytes. The variation of photosynthetic pathway types in the 105 studied species shows that 56.2% are C 3 , 41.0% are C 4 , 1.9% are CAM and 1.0% are C 3 -CAM. The C 3 pathway is more abundant in the halophytes, whereas the C 4 one is more common in the xerophytes, gypsophytes, gypso-halophytes and psamo-halophytes. The ratio of C 3 to C 4 species (C 3 /C 4 ratio) is 0.2 in the psamo-halophytes, 0.8 in the gypso-halophytes, 1.1 in the xerophytes, 1.6 in the xero-halophytes, 1.8 in the hygrohalophytes, 2.0 in the psamophytes and 3.8 in the halophytes. The annuals are mainly C 3 plants whereas most of perennials are C 4 ones. The C 3 /C 4 ratio is 1.3 in succulent species and 1.4 in non-succulent species. Thus, succulence seems not to affect the distribution of C 3 and C 4 pathways within the studied plants. This investigation shows high percentages of C 4 plants in plants of Tunisian arid regions. However, there are significant differences in their abundance among ecotypes. Based on C 3 /C 4 ratio, the abundance of the C 4 pathway is in the following order: psamo-halophytes, gypso-halophytes, xerophytes, xero-halophytes, hygro-halophytes, psamophytes, halophytes. In Tunisian arid regions, C 4 species are most abundant in xerophytes and less abundant in halophytes. In the Chenopodiaceae the number of C 3 plants is 13 and the number of C 4 species is 20 and in the Poaceae the number of C 3 was 23 and the number of C 4 was 19 species. Thus, the most C 4 proportion is in the Chenopodiaceae and Poaceae species. This confirms the fact that the Chenopodiaceae and the Poaceae were the leading families that tolerate salinity and aridity.