Resilience in aridity: from biomass reduction to antioxidant accumulation in sewan grass

Sewan grass is soil moisture deficit tolerant grass abundantly present in deserts of Pakistan. However, data regarding the natural structural and physiological adaptations under moisture deficit is not well studied. In all populations from various arid habitats main growth changes related to sewan grass were shoot fresh biomass decreased from 12.4 g (SoV) to 6.2 g (Cho), while root fresh biomass declined from 8.6 g (SoV) to 4.1 g (Cho). Leaf area was reduced from 3 cm² in SoV and NpT to 1 cm² in Cho and photosynthetic pigments with increase in Chlorophyll a from 2.45 mg g⁻¹ f.w. (SoV) to 0.0051 mg g⁻¹ f.w. in Cho, and root length for water requirement. Shoot tissue showed more accumulation of ions instead of root tissue for all populations. All antioxidative enzymes activities such as superoxide dismutase (SOD: 2.8 U mg⁻¹ protein), peroxidase (POD: 0.10 U µg⁻¹ protein), catalase (CAT: 0.60 U mg⁻¹ protein), ascorbate peroxidase (APX: 0.050 U mg⁻¹ protein) and organic osmolytes like glycine betaine (GB) and proline were increased by 45% and 52% respectively in Cho relative to SoV for better growth under moisture deficit. Major structural adaptations of hyper-arid Cho populations include thick sclerified tissues around cortical, vascular bundles and pith region of root and shoot. Likewise decreased epidermis thickness, cell area of epidermis, cortex and metaxylem vessels for better water conduction under soil moisture deficit. Based on the recorded structural and functional adaptations, the tolerance to soil moisture deficit can be ranked as Cho > NpT > SoV in all populations from arid habitats. In conclusion, small thick sclerified leaves and vascular bundles, longer roots and more antioxidative enzymes activities are the major features observed in sewan grass populations to induce soil moisture deficit tolerance.