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 C-4 grass grown in arid regions. This research work focused on assessing the growth of S. ciliata accessions 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. ciliata seedlings under different water treatments: T-1 (200 mm/a), T-2 (150 mm/a), T-3 (100 mm/a) and T-4 (50 mm/a). Growth phenology, net photosynthesis (P-n), stomatal conductance (g(s)), midday leaf water potential (psi(md)), predawn leaf water potential (psi(pd)), soil water content (SWC) and soil water potential (psi(s)) 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 T-1. The two accessions responded differently and significantly to water stress. Photosynthetic parameters, such as P-n and g(s), decreased sharply under treatments T-2, T-3 and T-4 compared to treatment T-1. 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 T-4 for accessions WA and DA, respectively. Principal component analysis (PCA) was applied, and the separation of S. ciliata accessions 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 T-1 and T-2. This accession was characterized by a high number of spikes. For treatments T-3 and T-4, both accessions were detected in the negative extremity of PC1 and PC2. They were characterized by a high root dry biomass. Therefore, S. ciliata accessions 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. ciliata exhibits a significant adaptation capacity for water limitation and may be an important species for ecosystem restoration.