| Medium and trace elements are important constituent of secondary metabolite synthases or secondary metabolites in plant,which play an important role in the growth of plant and the synthesis and accumulation of secondary metabolites.When plants suffer the deficit of essential micronutrients,its growth and development could be inhibited resulting in a decline of yield and quality.Hemp(Cannabis sativa L.)is a type of cannabis variety containing THC less than 0.3%.Its roots,stems,leaves,flowers and seeds have great value of development and application.In order to understand the effects of magnesium,boron,iron and manganese on the growth of hemp plant and the concentration of cannabinoid in leaves,the Yunnannese varieties ‘Yunma 7’ and‘Yunma 8’ were used as materials in this study.Sand culture was used to grow hemp seedlings.The control plants(CK)were irrigated with a modified Hoagland nutrient solution.Nutrient solutions deficient in magnesium,boron,iron and manganese were given respectively to the seedlings.There were two levels of nutrient deficiency,one contains the tested nutrient by 1/3 concentration of the CK and the other contains no tested nutrients.To further clarify the effect of nutrient deficient on plants,complete nutrient solution was supplemented to part of the plants suffering nutrient deficiency after symptoms appeared.Morphological changes of the plants were regularly observed during the since the start of deficient treatments.The plants treated with one nutrient were harvested when they were severely inhibited by nutrient deficiency.Dry matter weight,root vigor,and malondialdehyde,THC and cannabidiol(CBD)concentrations in leaves were determined.Key research findings are presented as follows:(1)After the start of magnesium treatment for 25 days,interveinal chlorosis appeared on the leaves.1/3 concentration of magnesium deficiency treatment had less chlorosis than that of complete magnesium deficiency treatment.45 days after magnesium deficiency treatment,the degree of chlorosis aggravated,and the edges of old leaves were scorched or completely withered;the leaf SPAD value,plants dry weight,root activity,and the concentrations of magnesium,CBD in leaves decreased with an increased in the level of magnesium deficiency,while malondialdehyde concentration in leaves increased;the dry weights of roots,stems and leaves of the complete magnesium deficiency treatment were 43%,31% and 56% lower than those of the control,while the CBD concentration in the leaves was 42% lower.Magnesium deficiency had no significant effect on the THC concentration in leaves.20 days after the restoration of magnesium supply,the SPAD value,dry matter mass,root activity and leaf magnesium concentration of the leaves of the completely magnesium-deficient plants were still lower than those of the control,but the color of the newly emerged leaves was similarly to that of control.The CBD concentration of the magnesium restored plants did not significantly differ to the control.(2)15 days after the start of complete boron deficiency treatment,new leaflets of the plants showed curling and chlorosis symptoms,while 1/3 concentration of boron deficiency treatment had no significant effect on plant leaf morphology.At 40 days after boron deficiency treatment,new leaves were spotted and the growth points were necrotic;plant height,leaf SPAD value,dry matter weight and CBD concentration in leaves decreased while malondialdehyde concentration in leaves increased.For the plants under the complete boron deficiency treatment,dry weights of roots,stems and leaves were 50%,43% and 60% lower than those of the control while CBD concentration in the leaves was 41% lower than.Root vigor and leaf boron content decreased with an increase in the levels of boron deficiency.Boron deficiency had no significant effect on THC concentration in leaves.25 days after the boron supply was restored,the curled leaves at the top of the completely boron-deficient plants returned to normal with the increase of the recovery time;the CBD concentration,SPAD value,root dry weight and malondialdehyde concentration did not differ from the control,but plant height,stem and leaf dry weight,and root vigor were still lower than those of the control.(3)60 days after of complete iron-deficient treatment,new leaves appeared interveinal chlorosis.1/3 concentration of iron deficiency treatment had no significant effect on plant leaf morphology.The new leaves turned yellow after 80 days of irondeficient treatment,partially whitish and spotted.At 80 days,the SPAD value,dry matter weight,CBD and THC concentrations in the leaves decreased,but the malondialdehyde concentration in the leaves increased.Under the complete iron deficiency treatment for 80 days,the dry weights of roots,stems and leaves of the plants were 30%,15% and 16% lower than those of control,and the CBD concentration in the leaves of Yunma 7 and Yunma 8 were 21% and 31% lower than those of the control,respectively.Leaf iron concentration and root activity decreased with an increase in iron deficiency.20 days after iron restoration,the CBD concentration was not significantly different from control,but the SPAD value,root activity,leaf iron concentration and THC concentration of the plants were still lower than those of control.(4)28 days after of complete manganese deficiency treatment,the new leaves appeared interveinal chlorosis,1/3 concentration of manganese deficiency treatment had no significant effect on plant leaf morphology.50 days after of manganese deficiency treatment,the chlorosis was aggravated,and the leaves curled and appeared brown spots;the SPAD value,plant height,dry matter weight,root activity and manganese concentration in leaves decreased with an increase in manganese deficiency,but the concentration of malondialdehyde in leaves increased.Under the complete manganese deficiency treatment for 50 days,the roots,stems and leaves of the plants were 43%,111% and 83% lower than the control,respectively.There was no significant difference in CBD,THC concentrations and CBD/THC ratio in leaves between manganese deficiency treatment and control.Twenty-two days after manganese supply was restored,leaf color of new leaves of completely manganese-deficient plants returned to normal green,but the leaves were still slender and curled,and the leaf SPAD value,stem,leaf dry weight and leaf manganese concentration were still lower than those of the control.To sum up,the deficiency of magnesium,boron,iron and manganese will affect the growth and physiological indicators of hemp plants.The response time to magnesium,boron and manganese deficiency was faster and the symptoms were more obvious,while the response time to iron deficiency was longer and the symptoms were milder.Therefore,magnesium,boron and manganese could be grouped to sensitive elements,and iron to insensitive. |
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