Phragmites karka plants adopt different strategies to regulate photosynthesis and ion flux in saline and water deficit conditions

Abstract

Phragmites karka (Retz.) Trin. ex Steud. is a pan-tropical, wetland, grass, and this study restricted water availability to P. karka by either low matric potential (water deficit) or low osmotic potential (salinity). Growth, water relations, mineral nutrition, and photosynthesis were compared when plants were irrigated at control (100% water holding capacity WHC), 300 mM NaCl (salinity, at 100% WHC), or water deficit (40% WHC) conditions. Leaf water potential and plant growth decreased substantially under salinity and water deficit. This led to stomatal closure and a decrease in gas exchange with the risk of oxidative injury. Under saline conditions, stress was mitigated by an increased dissipation of absorbed light energy by non-photochemical quenching. Water deficit conditions led to higher PS II quantum yield efficiency. Shoot Na⁺ toxicity was reduced by 10-fold higher Na⁺ sequestration in salt-treated roots, and enhanced proline and soluble carbohydrate accumulation in the leaf, compared to the control. Inorganic and organic substances maintained a higher soil-to-plant water gradient in salt-stressed plants compared to drought-stressed plants. P. karka survived in both forms of restricted water via growth plasticity, regulated osmotic and ionic homeostasis, and efficient gas exchange and PSII photochemistry.

Keywords:

• Halophytic giant grass
• ion homeostasis
• leaf gas-exchange
• osmotic stress
• photochemical efficiency
• sodium toxicity
• water relation

Disclosure statement

No potential conflict of interest was reported by the author(s).

Funding

This study was conducted under the auspices of Pakistan and German collaborative Project #: 1-308/ILPU/HEC/2009 “Biochemical, eco-physiological, anatomical and morphological stress responses of cash-crop halophytes” which was funded by the Higher Education Commission (HEC) Pakistan.

Table 2. Changes in the carbon (C), nitrogen (N), C/N ratio, nitrogen use efficiency (NUE), soluble sugar, and proline content of Phragmites karka leaves. Values are means ± SE. Bonferroni letters represent significant differences (P < 0.05) among treatments (Control: Well irrigated with water, salinity: 300 mM NaCl) and water deficit: 40% WHC).