Role of leaf micro-structural modifications in modulation of growth and photosynthetic performance of aquatic halophyte Fimbristylis complanata (Retz.) under temporal salinity regimes.

Fimbristylis complanata is an aquatic halophytic sedge that thrives in salt-affected land, marshes, and water channels. Two ecotypes (HR-Rasool headworks ECe 19.45; SH- Sahianwala 47.49 dS m) of F. complanata were collected from two salt-affected wetlands of Punjab, Pakistan. Five rhizomes of each ecotype were grown in plastic pots in the Botanical garden research area and treated with three intensities of salt [0 mM (control), 200 mM (moderate), 400 mM (high) NaCl for three durations (0, 15 and 30 days). The pots were arranged using a completely randomized block design (CRD) with three replications. After each duration, sampling was done. The HR ecotype optimally performed better under moderate salt incubation and moderate to higher salt exposure. This ecotype had improved growth traits, including shoot fresh weight (SFW), shoot dry weight (SDW), leaf area (LA), root length (RL), leaf mass fraction (LMF), relative growth rate (RGR), and unit leaf area (ULA) at higher NaCl (400 mM) in comparison with control NaCl (0 mM). This improvement in growth occurs due to the accumulation of photosynthetic pigments, better photosynthesis, and water use efficiency (A/E). The leaf microstructure increased in HR ecotype as midrib (MrT), leaf blade (LTh), bulliform cells (BTh), and cortical cells (CcT) thicknesses to prevent water loss under salinity, increase aerenchymatous area (ArA) for efficient gas movements at moderate salt levels and less exposure time concerning absolute control (0 mM NaCl). The SH ecotype affirmed more tolerance to salt by securing higher biomass (SFW, SDW), increased growth traits (LA, RL, LMF, ULA), photosynthetic pigments (Chl a, b, Car), and maximum photosynthetic performance at high salt regimes and prolonged duration in comparison to control (0 mM NaCl). Additionally, increased MrT, LTh, BTh, ECA, abaxial and adaxial stomatal area, and density, broadened metaxylem and phloem area, large aerenchyma, more cortical cell thickness under moderate to high salt regimes under moderate to high salt levels and time. Overall, changes in morpho-physiological traits and leaf microstructures in both ecotypes are linked to salt tolerance under temporal salt regimes. Our findings suggest that both ecotypes of F. complanata can potentially rehabilitate the salt-affected wetlands.