Abstract
The effects of salt-induced stress in drug-type Cannabis sativa L. (C. sativa), a crop with increasing global importance, are almost entirely unknown. In an indoor controlled factorial experiment involving a type-II chemovar (i.e., one which produces Δ9-tetrahydrocannabinolic acid ~THCA and cannabidiolic acid ~ CBDA), the effects of increasing NaCl concentrations (1–40 mM) was tested in hydroponic and aquaponic solutions during the flowering stage. Growth parameters (height, canopy volume), plant physiology (chlorophyll content, leaf-gas exchange, chlorophyll fluorescence, and water use efficiency), and solution physicochemical properties (pH, EC, and nutrients) was measured throughout the experiment. Upon maturation of inflorescences, plants were harvested and yield (dry inflorescence biomass) and inflorescence potency (mass-based concentration of cannabinoids) was determined. It was found that cannabinoids decreased linearly with increasing NaCl concentration: -0.026 and -0.037% THCA·mM NaCl-1 for aquaponic and hydroponic solutions, respectively. The growth and physiological responses to NaCl in hydroponic—but not the aquaponic solution—became negatively affected at 40 mM. The mechanisms of aquaponic solution which allow this potential enhanced NaCl tolerance is worthy of future investigation. Commercial cultivation involving the use of hydroponic solution should carefully monitor NaCl concentrations, so that they do not exceed the phytotoxic concentration of 40 mM found here; and are aware that NaCl in excess of 5 mM may decrease yield and potency. Additional research investigating cultivar- and rootzone-specific responses to salt-induced stress is needed.
Highlights
Rootzone salinity (NaCl) is a predominant stress factor that poses three main problems to glycophyte conventional field crops
NaCl concentration affected the growth and physiology of C. sativa plants grown in hydroponic solution but not those grown in the aquaponic solution
Plants grown in hydroponic solution at 40 mM NaCl had reduced growth index over time compared to plants grown at 1 and 10 mM NaCl hydroponic solutions, while NaCl did not have an effect on plants grown in aquaponic solution (Figures 1A, B)
Summary
Rootzone salinity (NaCl) is a predominant stress factor that poses three main problems to glycophyte conventional field crops. Solution Influence on NaCl-Stress in C. sativa agriculture system for water conservation and rootzone optimization (Rafiee and Saad, 2006; Oladimeji et al, 2018); these systems are not liberated from rootzone salinity. Plants cultivated in recirculating solution systems can accumulate Na+ and Cl- at concentrations found to be damaging for most greenhouse crops (e.g., 3–21 mM NaCl) (Beauchamp et al, 2018; Goddek and Vermeulen, 2018). As water is reused in recirculating systems, un-absorbed ions can accumulate to concentrations which create salt stress (i.e., 5–10 mM NaCl; Sonneveld et al, 1999; Neocleous and Savvas, 2017), or disrupt the uptake of other dissolved mineral nutrients. Na+ and Cl- often accumulate in these systems as a result of high Na+/Cl- containing source water and/or fertilizers, paired with low Na+/Cl- requiring crops (Stanghellini et al, 2005)
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