Effects Of Exogenous CaCl₂ On The Physiological Characteristics And Secondary Metabolites Of Cannabis Sativa L. Under Salt Stress

Soil salinity poses a serious threat to the limited land resources on which humans depend,and is a major stress of adversity that limits normal plant metabolism and development.Cannabis sativa L.,is an annual herb,in agriculture,chemicals,food,medical drugs and other fields have a very wide range of application prospects,is China’s special crops and products,with a wide range of medicinal value.Calcium is an essential nutrient for plant metabolism and development,and is involved in physiological metabolism and signalling in plants,which can well improve their adaptability to adversity.In this study,the physiological characteristics and the content of secondary metabolites of C.sativa seedlings under NaCl stress were analysed by applying different concentrations of exogenous CaCl₂to investigate the adaptability of C.sativa and the mitigating effect of CaCl₂on the growth of C.sativa under NaCl stress,in order to provide a theoretical basis for the cultivation of C.sativa in saline areas and the discovery of salt tolerance adaptations.The main results are as follows:（1）Under NaCl treatment,the transpiration rate（Tr）,net photosynthetic rate（Pn）,stomatal conductance（Gs）,maximum photochemical efficiency（Fv/Fm）and photosynthetic pigment content of C.sativa leaves gradually decreased with increasing salt concentration and time;when different concentrations of CaCl₂were applied,Tr,Pn,Gs,Fv/Fm and photosynthetic pigment content showed a trend of increasing and then decreasing,indicating that the application of CaCl₂at suitable concentrations could reduce the inhibition of C.sativa photosynthesis by NaCl treatment.（2）The contents of malondialdehyde（MDA）and proline（Pro）increased significantly under NaCl stress;the contents of soluble protein,soluble sugar and antioxidant enzyme activities increased and then decreased;when exogenous CaCl₂was applied,the contents of malondialdehyde decreased and then increased,while the contents of proline and antioxidant enzyme activities increased and then decreased.This indicates that the spraying of CaCl₂at the optimum concentration effectively reduced the degree of membrane lipid peroxidation and increased the content of osmoregulatory substances and the activity of antioxidant enzymes in C.sativa leaves.（3）The content of total flavonoids and cannabidiol（CBD）in C.sativa leaves showed an increasing trend followed by a decreasing trend under NaCl treatment.The highest accumulation of total flavonoids and CBD content in C.sativa leaves was achieved when exogenous CaCl₂at 5 mmol·L^-1and 10 mmol·L^-1was applied,indicating that CaCl₂at appropriate concentrations(10 mmol·L^-1)could alleviate the accumulation of secondary metabolites in C.sativa leaves by NaCl stress.To sum up,NaCl stress has a low-promoting and high-suppressing effect on the growth of C.sativa,and its concentration has a direct impact on the physiological indicators and the content of secondary metabolites of C.sativa.At low concentrations,it can resist the damage caused by salt stress to C.sativa by increasing the content of osmoregulatory substances and antioxidant enzyme activity;applying a certain concentration of CaCl₂can effectively reduce the damage caused by NaCl stress to C.sativa,thus improving the resistance of C.sativa in salt-damaged environment.