Abstract
Salinity and drought are two often simultaneously occurring abiotic stresses that limit the production of food crops worldwide. This study aimed to distinguish between the separate and combined impacts of drought and salinity on the plant response. Panicum antidotale was cultivated in a greenhouse under the following growth conditions: control, 100 mM NaCl (100) and 300 mM NaCl (300) salinity, drought (D; 30% irrigation), and two combinations of salinity and drought (100 + D and 300 + D). The growth response was as follows: 0 ≈ 100 > 100 + D > > D ≈ 300 ≈ 300 + D. Growth correlated directly with photosynthesis. The net photosynthesis, stomatal conductance, intercellular CO2, transpiration, ribulose 1,5-bisphosphate carboxylase (Rubisco), ribulose 1,5-bisphosphate (RuBP) regeneration, and triose phosphate utilization protein (e.g., phosphoenolpyruvate carboxylase) were highest in the control and declined most at 300 + D, while 100 + D performed significantly better as compared to drought. Maximum and actual photosystem II (PSII) efficiencies, along with photochemical quenching during light harvesting, resemble the plant growth and contemporary CO2/H2O gas exchange parameters in the given treatments. Plant improves water use efficiency under salt and drought treatments, which reflects the high water conservation ability of Panicum. Our findings indicate that the combination of low salinity with drought was able to minimize the deleterious effects of drought alone on growth, chlorophyll content, cell integrity, photosynthesis, leaf water potential, and water deficit. This synergetic effect demonstrates the positive role of Na+ and Cl– in carbon assimilation and osmotic adjustment. In contrast, the combination of high salinity and drought enforced the negative response of plants in comparison to single stress, demonstrating the antagonistic impact of water availability and ion toxicity.
Highlights
The rapid change in global climate threatens plant growth and productivity worldwide
The water potential of leaves showed a similar trend, with the exception of the 100 + D treatment, where it was similar to the control and 100 mM NaCl-treated plants
The maximum photosynthesis rate (Pn) was recorded under 100 mM NaCl treatment and the lowest value was observed under 300 + D treatment
Summary
The rapid change in global climate threatens plant growth and productivity worldwide. These changes are seriously abrupt and can be present in combinations at any given time (Qadir et al, 2014). The number of studies to unravel the combined effect of multiple stress factors on plants’ productivity are very few (Mittler, 2006; Zandalinas et al, 2018). A progressive and consecutive development of drought and salinity stress decreases the availability of cultivable land (Abdelraheem et al, 2019). This alarming situation should be resolved at the earliest. A detailed understanding of the interactions of both stressors on plant growth needs to be undertaken
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