Effects of Climate Change on the Mediterranean Stipa tenacissima L. Steppes Through an Ecophysiological Perspective

Predicting the future impact of climate change on Stipa tenacissima is crucial to realize the potential of the future risks on Alfa grass steppes in southwest Europe and North Africa. The degradation of Alfa grass steppes due to the impact of global warming and human activities lead to desertification progress and land degradation. A comparative study of ecophysiological adaptations of S. tenacissima populations is an attempt to understand the ecological adaptations of this species. We selected seven populations, representing a precipitation range from 100 (Sfax, Tunisia) to 600 (Valencia, Spain) mm/year at the sites of seed collection. Seedlings were established in a common garden on Guadamar, Spain. Gas exchange measurements of CO₂ and light response curves on S. tenacissima were conducted on seven seedlings per population to simulate the expected response of the species under limiting environmental conditions. Chlorophyll content and isotopic analysis were also analyzed to study the physiological differences between populations (post hoc S-N-K test at P < 0.05 level). There was a difference among populations on net photosynthesis where Thala (Kasserine, Tunisia) and Valencia (Spain) populations showed a contrasting response. However, these contrasted populations showed similar response in the maximum rate of carboxylation (Vcmax) and the maximum rate of electron transport (Jmax). Stipa tenacissima populations showed a variable response in relation to different light intensities. In fact, photosynthesis and chlorophyll fluorescence parameters were significantly different among populations in response to light intensities (0, 25, 500, 1000, and 1500 μmol m⁻² s⁻¹). Populations possessed a similar chlorophyll content. The isotopic analysis highlighted a different carbon and nitrogen isotopic composition (δ¹³C and δ¹⁵N) and carbon content (C) among populations. However, the variability of populations is probably related to the genetic and not to climate, as no potential relationship between the studied physiological traits and climate variables at the study site was found. In relation to climate change, S. tenacissima seedlings could meet a serious risk that impaired their survival and growth. Extension of drought period already long in arid land could enhance mortality by carbon starvation and lack of photo-inhibition. Hence, elaboration of a protection program of Alfa grass steppes to degradation and understand the species behavior and adaptation could be useful to avoid the desertification progress.