| After the completion and operation of the Three Gorges Dam Project,a hydro-fluctuation belt with a water level drop of 30 m and an area of 350 km2was formed.This hydrological rhythm has caused a series of ecological problems within the reservoir area’s ecology,such as the loss of original vegetation,decrease of biodiversity,severe soil erosion.As a result,the ecological structure and function of the hydro-fluctuation belt of the Three Gorges Reservoir Area（TGRA）have been damaged.Therefore,the restoration and reconstruction of vegetation in this area are of great significance.Taxodium distichum and Taxodium distichum var.imbricatum grow rapidly and have strong submerging-resistance ability,they are excellent species for artificial vegetation reconstruction in the hydro-fluctuation belt of the TGRA.Different provenances and individuals of these two species have different tolerance to various stresses,so it is necessary to select individuals with high resistance for afforestation.Therefore,in order to cultivate a large number of fine and strong seedlings of T.distichum and T.distichum var.imbricatum to meet the needs of vegetation restoration and reconstruction in the TGRA,it is necessary to study the cutting propagation of T.distichum and T.distichum var.imbricatum which are growing in situ in the hydro-fluctuation belt of the TGRA.In this study,the T.distichum and T.distichum var.imbricatum planted in the vegetation restoration demonstration base of the TGRA in Zhong County,Chongqing City,were used as the experimental materials.The cutting propagation techniques of these two species were studied from different exogenous hormones,their concentrations treatment time and different cutting methods.Besides,the rooting mechanisms were studied by analyzing the dynamic changes of nutrient contents and oxidase activity,it aims to provide a theoretical reference for cutting propagation of T.distichum and T.distichum var.imbricatum.The results are as follows:（1）Exogenous hormones and treatment times had significant effects on the rooting traits of T.distichum cuttings.The rooting rate of cuttings treated with hormone varied from 13.33%to 65.00%,while that treated with distilled water（the control group）was only 13.33%.The most important factor affecting the T.distichum cuttings was the type of exogenous hormone,followed by the treatment time,and the hormone concentration had no significant effect on the cuttings.Among these 4 exogenous hormones,IBA+NAA had the best effectiveness,followed by ABT rooting powder and IBA（Indolebutyric acid）,and NAA（Naphthalene acetic acid）was the poorest.Among these4 treatment times（3 h,6 h,9 h and 12 h）,the treatment time of 6 h had the best effectiveness.There was no significant difference in facilitating rooting of the cuttings among these 4 concentrations(50 mg·L-1,100 mg·L-1,150 mg·L-1,200 mg·L-1).Among the 17 treatments（16 hormone treatment groups and 1 control group）,150 mg·L-1×6 h×（IBA+NAA）and 50 mg·L-1×12 h×（IBA+NAA）had the highest rooting rates of 65%and 55%,respectively.The rooting rate of T.distichum var.imbricatum cuttings was extremely low,only 0-6.67%.Exogenous hormone had no significant promoting effect on the cutting rooting of T.distichum var.imbricatum,and there was no significant difference in rooting traits among 17 treatments.（2）Cutting methods had significant effects on the rooting traits of T.distichum cuttings.Among these five cutting methods（right angle cutting,inclined cutting,double-sided cutting,radial cutting and longitudinal carving）,the longitudinal carving treatment had the best effectiveness.There was no significant difference in rooting traits of T.distichum var.imbricatum cuttings among these 5 cutting methods.（3）Adventitious roots protruding from both bark and callus of T.distichum cuttings,some of these cuttings did not form callus at the incision,indicating that the formation of callus from the base incision was not necessary for adventitious root formation.The cutting rooting process of T.distichum cuttings treated by IBA was divided into the following three stages:0-30 d for adventitious root induction;30-40 d for adventitious root expression;after 40-50 d for adventitious root elongation.The bark rooting was the main way of rooting of T.distichum var.imbricatum cuttings,there was no adventitious roots protrude from the callus.At 30 d after cuttings planting,the adventitious roots appeared in very few of T.distichum var.imbricatum cuttings,and most of cuttings died.（4）During the cutting process of T.distichum cuttings,the soluble sugar content of cuttings treated with distilled water and IBA showed a trend of“up-down-up”and“up-down-up”respectively,and the peak value of soluble sugar content of the IBA treatment group appeared earlier than the control group.The variation trend of soluble protein of T.distichum cuttings of these two treatments were similar to that of their soluble sugar content.The starch content of T.distichum cuttings treated by control showed a trend of continuous decreasing,while that of the cuttings treated by IBA showed a trend of“down-up”,and the starch content of the IBA treatment group was consistently lower than that of the control group during the adventitious root induction phase.The above results indicated that the exogenous hormones accelerated the accumulation of soluble sugar and soluble protein,promoted the hydrolysis and transformation of starch,and were beneficial to the cutting rooting of T.distichum.During the cutting process of T.distichum var.imbricatum cuttings,both the soluble sugar content of cuttings treated with distilled water and IBA showed the same trend of“up-down”,and the content of starch and soluble protein of cuttings of these two groups decreased continuously until the cuttings died.There was no significant difference in nutrients between the these treatments,indicating that exogenous hormones had no significant effect on the metabolism of nutrients of the T.distichum var.imbricatum cuttings.（5）During the cutting process of T.distichum cuttings,the activities of IAAO（indole acetic acid oxidase）,POD（peroxidase）and PPO（polyphenol oxidase）of cuttings in both the control group and IBA treatment group showed a trend of"up-down".The peak values of these three enzyme activities of the IBA treatment group were higher than those of the control group,indicating that the exogenous hormones increased the activities of IAAO,POD and PPO of the cuttings,thereby promoting the rooting of T.distichum cuttings.During the cutting process of T.distichum var.imbricatum cuttings,exogenous hormones increased the IAAO activity of cuttings temporarily.After 10 d of cutting planting,the IAAO activity of cuttings of these two groups continued to decrease until the cuttings died.The POD activity of T.distichum var.imbricatum cuttings of these two groups increased during 0-10 d,and then continued to decrease.PPO activity of these two groups did not change significantly during 0-10 d,and continued to decline afterwards.There was no significant difference in the activities of POD and PPO between the IBA treatment group and the control group,indicating that exogenous hormones did not affect the activities of POD and PPO of T.distichum var.imbricatum cuttings.In conclusion,the suitable hormones treatments for cutting propagation of T.distichum grown in the Hydro-fluctuation Belt of TGRA were 150 mg·L-1×6h×（IBA+NAA）and 50 mg·L-1×12 h×（IBA+NAA）,and the suitable cutting method was longitudinal carving.Exogenous hormones accelerated the process of nutrient synthesis and metabolism,increased the activity of IAAO,POD and PPO of cuttings,thus promoted the formation of adventitious roots.The rooting rate of T.distichum var.imbricatum cuttings is extremely low,except for IAAO activity,exogenous hormones had no effect on the nutrients content and oxidase activity of cuttings.The reasons for the difficulty in rooting of T.distichum var.imbricatum cuttings are unclear,and further research is needed. |
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