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Biological invasion represents a major worldwide threat to native biodiversity and environmental stability. Haloxylon persicumwas introduced to Tunisia (North Africa) with Saharan bioclimate in 1969 to fix sandy dunes. Since then, it has gained significant interest for its potential to colonize, proliferate, and become naturalized in Tunisia. Hence, understanding the seed germination response of H. persicumto abiotic conditions, including temperature, water stress, and salt stress, is crucial for predicting its future spread and adopting effective control strategies. Our work investigated the germination behavior of this invasive plant species by incubation at temperatures from 10.0°C to 35.0°C and at various osmotic potentials (−2.00, −1.60, −1.00, −0.50, and 0.00 MPa) of polyethylene glycol-6000 (PEG6000, indicating water stress) and sodium chloride (NaCl, indicating salt stress) solutions. Results showed remarkable correlations among the seed functional traits of H. persicum, indicating adaptive responses to local environmental constraints. The maximum germination rate was recorded at 25.0°C with a rate of 0.39/d. Using the thermal time model, the base temperature was recorded at 8.4°C, the optimal temperature was 25.5°C, and the ceiling temperature was found at 58.3°C. Besides, based on the hydrotime model, the base water potential showed lower values of −7.74 and −10.90 MPa at the optimal temperatures of 25.0°C and 30.0°C, respectively. Also, the species was found to have excellent tolerance to drought (water stress) compared to salt stress, which has implications for its potential growth into new habitats under climate change. Combining ecological and physiological approaches, this work elucidates the invasive potential of H. persicumand contributes to the protection of species distribution in Tunisian ecosystems.

Stipagrostis ciliata(Desf.) De Winter is a pastoral C4grass grown in arid regions. This research work focused on assessing the growth of S. ciliataaccessions derived from two different climate regions (a wet arid region in the Bou Hedma National Park in the central and southern part of Tunisia (coded as WA), and a dry arid region from the Matmata Mountain in the south of Tunisia (coded as DA)) under water stress conditions. Specifically, the study aimed to investigate the phenological and physiological responses of potted S. ciliataseedlings under different water treatments: T1(200 mm/a), T2(150 mm/a), T3(100 mm/a) and T4(50 mm/a). Growth phenology, net photosynthesis (Pn), stomatal conductance (gs), midday leaf water potential (Ψmd), predawn leaf water potential (Ψpd), soil water content (SWC) and soil water potential (Ψs) were observed during the water stress cycle (from December 2016 to November 2017). The obtained results showed that the highest growth potential of the two accessions (WA and DA) was recorded under treatment T1. The two accessions responded differently and significantly to water stress. Photosynthetic parameters, such as Pnand gs, decreased sharply under treatments T2, T3and T4compared to treatment T1. The higher water stress increased the R/S ratio (the ratio of root dry biomass to shoot dry biomass), with values of 1.29 and 2.74 under treatment T4for accessions WA and DA, respectively. Principal component analysis (PCA) was applied, and the separation of S. ciliataaccessions on the first two axes of PCA (PC1 and PC2) suggested that accession DA was detected in the negative extremity of PC1 and PC2 under treatments T1and T2. This accession was characterized by a high number of spikes. For treatments T3and T4, both accessions were detected in the negative extremity of PC1 and PC2. They were characterized by a high root dry biomass. Therefore, S. ciliataaccessions responded to water stress by displaying significant changes in their behaviours. Accession WA from the Bou Hedma National Park (wet arid region) showed higher drought tolerance than accession DA from the Matmata Mountain (dry arid region). S. ciliataexhibits a significant adaptation capacity for water limitation and may be an important species for ecosystem restoration.

Most ecological studies in North Africa reveal a process of continuous degradation of rangeland ecosystems as a result of overgrazing. This degradation appears across the decreasing of perennial grass diversity. Indeed, the majority of steppe ecosystems are characterized by a low density of perennial grass species at present. This study evaluated the effects of temperature and water limitation on the seed germination of Stipagrostis ciliata(Desf.) de Winter, a perennial grass species. The seeds were collected from the Bou Hedma Park, Sidi Bouzid Governorate, Central Tunisia. The thermal time and hydrothermal time models were used to describe the seed germination of S. ciliataunder different water potentials and temperatures. The germination response of S. ciliataseeds in darkness was evaluated over a range of temperatures (15°C, 20°C, 25°C, 30°C and 35°C) and across a wide range of osmotic potentials (0.0,–0.2,–0.6,–1.2,–1.6 and –2.0 MPa) of the polyethylene glycol (PEG6000) solutions at each temperature level. Among the tested temperatures, 25°C was found to be the optimal temperature to the germination of S. ciliataseeds. The final germination percentage (75.2%) was obtained with distilled water. The progressive decrease of osmotic potential of the PEG6000solutions inhibited the seed germination. However, the number of days to first germination was increased with a reduction of osmotic potential. A significant positive relationship was identified between final germination percentage of S. ciliataseeds and osmotic potential of the PEG6000solutions, with R2ranging from 0.5678 to 0.8761. Furthermore, a high degree of congruency between predicted and observed germination time course curves was observed. In general, S. ciliataexhibits a significant adaptation capacity for water limitation and high temperature in arid ecosystems.