Seasonal Differences in Ecophysiological Performance between Resprouters and Non-Resprouters across an Aridity Gradient in Northwest Tunisia

Understanding the functioning of shrub species during dry periods is necessary to forecast ecosystem responses to future climates, particularly in Mediterranean environments. We evaluated the seasonal changes in leaf gas exchange, hydraulic traits, carbon and nitrogen isotopes, and non-structural carbohydrates of seeders and resprouting shrub species typical of Aleppo pine forests across an aridity gradient in Tunisia: Djebel Zaghouan (subhumid climate), Djebel Mansour (semiarid transitional climate), and Djebel El Sarj (semi-arid climate). We monitored seven woody species: Pistacia lentiscus, Erica multiflora, Phillyrea latifolia (resprouters), Cistus monspeliensis, Rosmarinus officinalis (seeders), Globularia alypum, and Calicotome villosa (resprouters-seeders). The seasonal variation in leaf water content was usually higher in seeders than in resprouters and was associated with higher resistance to embolism. In contrast, the seasonal variation in non-structural carbohydrates was higher in resprouters, especially at the driest site. Both delta C-13 and delta N-15 displayed seasonal enrichment-depletion patterns, with seeders showing an overall higher delta C-13 in summer than in spring, consistent with a water-saving strategy of increasing water use efficiency. Discriminant analysis suggested that resprouters can sustain a positive carbon balance during drought periods. The differential impact of summer droughts on water status and the ecophysiology of these plant strategies may lead to different ecosystem dynamics depending on whether climate change tips the balance towards a preponderance of stressors (drought) or disturbances (fire) in dry Mediterranean areas.

Automated summary

Understanding the functioning of shrub species during dry periods is crucial for predicting ecosystem responses to future climates in Mediterranean environments. In this study, we assessed the seasonal changes in various traits of seeders and resprouting shrub species across an aridity gradient in Tunisia. The results showed that seeders had higher leaf water content variations and resistance to embolism compared to resprouters. On the other hand, resprouters had higher seasonal variations in non-structural carbohydrates, especially in the driest site. Both seeders and resprouters exhibited seasonal patterns of isotopes and discriminating analysis indicated that resprouters could maintain positive carbon balance during drought periods.