Effects of water stress on growth phenology photosynthesis and leaf water potential in Stipagrostis ciliata(Desf.) De Winter in North Africa

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.