Morphological and ecophysiological responsiveness of Stipa tenacissima L. populations along a Mediterranean climatic gradient

Predicted climate change in the Mediterranean region has raised concerns about the possible impacts on Alphagrass (Stipa tenacissima L.) steppes. To understand the vulnerability degree and acclimation capacity of S. tenacissima populations to climate warming and the CO2 mitigation potential of Alfa steppes, we measured the physiological and morphological traits in five populations across a Mediterranean rainfall range from 100 to 600 mm/year. Results showed different response patterns to the precipitation gradient. Major differences were found in the gas exchange and leaf traits in the mesic to xeric sites. Xeric populations exhibited moderate gas exchange rates together with thicker and smaller leaves (i.e., low leaf dry matter content (LDMC), and high leaf thickness (Lth). They also presented differences in several functional traits related to water economy and earlier stomatal closure with drought. Furthermore, internal water use efficiency (IWUE) and apparent carboxylation efficiency (CE) were the lowest, and dark respiration (RD) was the highest in the arid site (Sfax) due to high temperatures. The relative water content at the turgor loss point (RWCtlp) varied from 0.91 to 0.85 from mesic to xeric sites, which demonstrates a high degree of osmotic adjustment. The leaf water retention capacity by osmotic adjustment and high cell turgor with a reduction in gas exchange activity through stomatal closure promote to S. tenacissima a sustain physiological activities under severe drought. These results suggest that S. tenacissima may have high adaptability to drought by regulating physiological activity and maintaining turgor pressure associated with suitable leaf structure.