Response Of Plant Growth And Fiber Cell Development Of Hemp (Cannabis Sativa L.) To Nitrogen Nutrition

The response characteristics of hemp varieties to nitrogen nutrition serves as the therotical basis for breeding of high-nitrogen-efficiency cultivars and formulation of cultivation technique with limited nitrogen consumption.In this experiment,nitrogen source provided with KNO3 and NH4NO3,four hemp varieties(Wanma 1,Bama Huoma,Yunma 5,Yunma 7)were used to explore the suitable nitrogen concentrations for hemp growth and the effects of different nitrogen concentrations(0.30,0.75,1.50,3.00,6.00 and 12.00mmol/L)on the growth,physiology and fiber development of hemp.Using the fuzzy comprehensive evaluation methods,low nitrogen and high nitrogen tolerance varieties were assessed.The main results were as follows:1.Hemp growth adapted a wide range of nitrogen concentration under hydroponic conditionsThe growth of four hemp varieties under four levels of(0.30,1.50,3.00 and 6.00mmol/L)nitrogen treatments varied significantly.The overall growth of hemp was not good under low nitrogen concentration(0.30mmol/L).There were no significant differences in biomass,plant of height,stem thick and root/shoot ratio among four hemp varieties,under 3.00 and 1.50 mmol/L nitrogen concentrations.Hemp grew normally under high nitrogen concentration(6.00mmol/L)showing no stress symptom of oversupply nitrogen.2.Too low or too high concentration of nitrogen gave negative effects to hemp growth under hydroponicsCompared with 1.50 mmol/L nitrogen concentration,the biomass of four hemp varieties decreased under low or high nitrogen concentration,e.g.Bama Huoma significantly decreased under low nitrogen concentration and Yunma 7 significantly decreased under high nitrogen concentration.The seedling height of Yunma 5,the stem diameter of Bama Huoma significantly decreased and root/shoot ratio of Bama Huoma significantly increased under low nitrogen concentration.The seedling height,stem diameter and root/shoot ratio of Bama Huoma significantly increased,but these characters of Yunma 7 decreased under high nitrogen concentration.3.Physiological responses to nitrogen concentration showed varietal differenceCompared with 1.50 mmol/L nitrogen concentration,the physiological index of the four hemp varieties decreased or increased under low or high nitrogen concentrations.The chlorophyll and soluble protein content of Wanma 1 and the nitrate reductase(NR)activity of Yuma 5 significantly decreased,the superoxide dismutase(SOD)activity of Yunma 7,the malondialdehyde(MDA)content of Yunma 5 and soluble sugar content of Wanma 1 significantly increased under low nitrogen concentration.The chlorophyll and soluble protein content of Yunma 7 significantly increased under high nitrogen concentration.MDA and nitrate nitrogen content of Yunma 7,NR activity and soluble sugar content of Yunma 5,and SOD activity of Bama Huoma significantly decreased under high nitrogen concentration.4.Supplied concentration of nitrogen changed the efficiency of nitrogen,phosphorus and potassium in hempWith the increase of nitrogen supply levels,of the four hemp varieties,the nitrogen use efficiency showed decreasing tendency,the phosphorus use efficiency decreased firstly then increased,the potassium use efficiency also decreased except for Yunma 7.5.The tested hemp varieties showed different adaptation to low or high nitrogen concentrationsSubordination function analysis based on 13 indexes(including biomass)was used to evaluate adaptability of the four hemp varieties to nitrogen deficiency with the results as Yunma 7>Bama Huoma>Yunma 5>Wanma 1,and to oversupply nitrogen as Bama Huoma>Yunma 5>Yunma 7>Wanma 1.6.Nitrogen deficiency evidently stunted fiber cell development in hempThe development of hemp bast fiber cell under low nitrogen concentration was significantly deficient than that under 1.50 mmol/L nitrogen treatment,showing weaker fiber cell walls,abnormal fiber bundles,and less fiber cells in the bundles.