Studies On The Features Of Cutting Propagation And Growth As Well As The Tolerance To Heavy Metal Manganese In Giant Reed(Arundo Donax)

Giant reed?Arundo donax L.?,also known as reed,is a tall perennial herbaceous plant of the family Arundinoideae,Poaceae.Giant reed has the features of large biomass,rapid growth,strong propagational ability,and resistance to many heavy metals.Manganese?Mn?is an essential trace element in the process of plant growth and development,which involves in some important metabolic reactions in plants.However,high Mn content in plants will restrict the growth of plants.With the development and utilization of manganese ore resources,environmental pollution brought by tailings slag and abandoned land has also emerged.Manganese ore wasteland occupies a large amount of land and is an important source of soil and water pollution,on where can grow and survive only a few species of plants.Therefore,the treatment of Mn-contaminated soil has become an urgent and important research topic.In this paper,giant reed from tissue culture seedlings planted in the experimental base of Jishou University were employed as the research material.The cutting propagation characteristics of the lateral branches in summer and the effects of different fertilization models on growth and biomass of the crop were studied.The characteristics of physiology and biochemistry of giant reed under Mn stress were studied by hydroponic experiment.The tolerance and enrichment ability of this species to Mn were studied by hydroponic test in laboratory and field test in manganese ore wasteland in Luxi County,the western region of Hunan Province.The main results of this experiment are as follows:1.In the case of giant reed cutting in summer,pre-soaking with 0.8mg/L NAA and1.25g/L strong rooting agent of the lateral branches in solutions of plant growth regulators for 2 h was an effective way to increase the cutting survival rate.0.8 mg/L NAA solution had a survival rate of 50%,while 1.25 g/L strong rooting agent showed a survival rate of 43.33%.2.According to the effect of fertilization on the biomass of giant reed over through3 years,the biomass of single plant?dry and fresh weight?and different parts of the plant were affected by the fertilization model.During the 3 years test period,the plants were fertilized for twice,once and non-fertilization in the 1^st year,and no fertilization in the next two years.The results showed that the biomass of fertilization twice group was higher than those of fertilization once group in the 1^st and 2^nd year,and the biomass of non-fertilization group was always the least.The difference between fertilization groups and non-fertilization group was significant.The biomass in the 3^rd year exhibited the fertilization once group was higher than the twice group,and the non-fertilization group was lower than the former two groups.However,there was no significant difference between the fertilization treatments and non-fertilization treatment.The biomass of the crop increased during the period of 3 years,while the effects of fertilization were not significant at the 3^rd year.So,it was suggested to apply base fertilizer when planting and topdressing urea after a given interval time in the 1^st year,and fertilization once in the2^nd year,then no more fertilization in the latter years.The aboveground parts of giant reed could be harvested and utilized at the end of the 3^rd year.3.Mn stress had effects on the chlorophyll content and other physiological and biochemical indexes for giant reed leaves.Mn stress imposed less influence on chlorophyll content,and more influence on relative conductivity and SOD activity.The relative conductivity of plant leaves were generally increased after continuous Mn stress treatment for 32 days.The relative osmotic rate of the leaves reached 98.90%at the concentration of 1.0 mmol/L of Mn solution,which was significantly higher than that of the control group?32.07%?.Then followed the second and third differences in permeability of 59.60%and 66.62%at 0.2 mmol/L and 1.4 mmol/L,respectively,which were significant higher than that of the control group.The changes of proline and MDA under Mn stress performed similarly,showing that the content of proline and MDA decreased at first and then increased slowly and decreased again to the lowest level.The effect of Mn stress on antioxidant enzyme activity was also studied in this paper.It showed that the activity of POD decreased firstly and then increased.At the end of the test,the activity of Mn²⁺decreased at 1.4 mmol/L and increased at 0.2 mmol/L,indicated that low concentration of Mn promoted the activity of POD,and high concentration of Mn inhibited the activity of POD.Mn stress could accelerate the activity of CAT,and the promotion effects were positively correlated with the longer stress time and the higher Mn concentration.The activity of SOD decreased to the minimum at the Mn²⁺concentration of 1.0 mmol/L and 1.4 mmol/L at the end.The activity of SOD at 1.4mmol/L was only 16.67%of the control,which indicated that this concentration could inhibit the activity of SOD and even upset the systematic balance of SOD protection enzyme in giant reed.4.The photosynthesis characteristics of giant reed leaves were changed under Mn stress.Mn stress decreased the net photosynthetic rate?Pn?,stomatal conductance?Gs?and transpiration rate?Tr?,while increased the intercellular carbon dioxide concentration?Ci?.Pn dropped significantly at the concentration of 0.6 mmol/L of Mn during the second round of photosynthetic determination,which meant that the photosynthetic metabolic process of giant reed was inhibited and damaged in the medium and high Mn conditions over a certain time.Furthermore,the lowest value of Pn was found at the Mn concentration of 1.0 mmol/L.However,Tr at this concentration was not the lowest but kept the relative stable trend compared to those at adjacent concentrations.This phenomenon inferred that under high Mn stress,the stable Tr change was due to the enhanced absorption of water and nutrient elements involving the physiological metabolism and thus relieving the toxicity of Mn,which may be one of the reasons for the tolerance of the crop to Mn.The decreased Pn and increased Ci at high Mn concentration revealed that the main reason for the decrease of photosynthetic rate was due to the non-stomatal restriction.5.The contents of Mn in aerial?or above-ground?parts and underwater?or under-ground?parts of giant reed cultivated in hydroponic tanks with different Mn concentration and manganese ore wasteland were determined,and the biological accumulating coefficient?BAC?and biological transfer coefficient?BTC?of giant reed to Mn were also tested.The results found that giant reed had good tolerance to Mn,but it did not meet the criterion of super-enriched plants and could not be categorized as the super-enriched plant of Mn.The experiment presented that the contents of Mn in underwater?under-ground?parts of giant reed were higher than those of aerial or above-ground parts,especially for those of plants cultivated in hydroponic tanks.For example,the Mn content in under water part was more than 10000 mg/kg when it grew at the solution with Mn concentration of 0.1 mmol/L,which was significantly higher than that of the control.Furthermore,the Mn content even reached 25960 mg/kg when the underwater part grew at the Mn concentration of 1.0 mmol/L.Even the absorption and accumulation of Mn in the plant began to decrease at the Mn concentration of 1.0mmol/L and more,the Mn contents in the plant were still significantly higher than those of controls.The higher abilities of absorption and accumulation of Mn without exhibiting obvious toxic symptoms under the stress of high-concentration of Mn,indicated giant reed had good tolerance to this heavy metal.In the field experiment in manganese ore wasteland,the value of BAC and BTC of the above-ground parts cultivated in 1/3 soil+2/3 slag sample,1/2 soil+1/2 slag sample were all larger than the value of 1.0.However,the contents of Mn in the above-ground parts were not exceeded 10000 mg/kg,which meant giant reed could not be classified into the super-enriched plant of Mn,according to criterion.At the same time,it could be seen from the experiment that the height and biomass of the giant reed were the same,with the increase of Mn concentration,the accumulation of height and biomass decreased,under the two experimental designs.To sum up,the physiological and biochemical characteristics,growth features and Mn content of giant reed under Mn stress were analyzed in this chapter.The results showed that giant reed was a tolerant plant to Mn,although it did not meet the criteria of super-enriched plant of Mn.The favorable characteristics of the species such as large biomass,developed root system,rapid propagation and strong adaptability,make it a promising species for ecological restoration to manganese ore wasteland.Due to the density,compactness,poor aeration,strong acidity,high electrical conductivity and low fertility of the wasterland,it is suggested that suitable ratio of soil samples should be mixed with the slag in order to increase the aeration performance of the soil matrix,in the remediation of manganese ore wasteland with planting giant reed.