Abstract (eng)
The objective of this study was to quantify osmotic adaptation (osmolality) and the complex of chemiphysiological attributes of representative species of two families (Brassicaceae and Fabaceae), along an altitude- and precipitation- gradient from the hyper-arid desert to the dry high mountains of the High Atlas of South Morocco. Inorganic cations and anions, organic acid-anions, soluble carbonhydrates (incl. cyclits), free amino acids, total carbon and nitrogen as well as the signature of stable C- and N-isotopes were measured. Thus, it is an additional contribution to the physiotype-concept and, therefore, the better understanding of the adaptional potential of the named taxa to arid and semiarid environments, as well as the dry and cold climates of the southmediterranean high mountains.
The representatives of both families showed high amounts of calcium, potassium and magnesium but only trace amounts of sodium. In consideration of the patterns of inorganic anions taxonomical differences are visible: The Brassicaceae-species accumulated more sulphate while the Fabaceae-species enhanced phosphate. Fabaceae in general accumulated less organic acids than Brassicaceae, particularly regarding malate. Vella mairei (Brassicaceae) was the only species showing considerable amounts of cis-aconitate.
Both families have the ability to enhance greater or lesser amounts of so-called compatible solutes in dependence on the level of stress occurring at the collection sites. In that Brassicaceae preferred proline as compatible solute (up to 460 µmol/mL - Farsetia occidentalis), whilst Fabaceae favoured cyclic sugaralcohols (cyclitols), especially pinitol (up to 153 µmol/mL - Retama raetam).
Different ecological factors along the transect resulted in a strong variability of total amounts of the characterised substances, but did not affect the family-specific pattern. Neither did high mountain species show outstanding differences to species collected at low level (semi-) arid sites.
Average total amounts of osmotically active substances varied slightly in the course of the year, probably due to surpassing frequent precipitation events during the summer of 2003.
The analysis of isotopic signatures (12C/13C, 14N/15N) showed that all investigated species can be classified as C3- physiotypes using d13C-data. The comparison of spring- and autumn- data provided a strong indication of a rather humid summer period. Monthly precipitation-data confirms our interpretation for some sites.
A comparative measurement of dry matter (bulk) and tissue sap provides differentiated insights: Lower (more negative) d13C-data of drymatter versus tissue sap probably demonstrate an exceedingly high turnover of soluble carbon-compounds, as well as the stress-determinated point (in time) when the growth of tissue in the plant accelerates.
The measured d15N-data confirmed a 50 to 70 percent usage of symbiontic nitrogen in all species of Fabaceae, whereas d15N-data for Brassicaceae (naturally) indicated soil-N utilisation only.