Coupling Of Aluminum And Phosphate On Camellia Seedlings Growth And The Impact Of Physiological Indicators

As one of four major woody oil plants in the word,Camellia oleifera is the specific woody oil plant in China and it is mainly distributed in acid-soil areas of Southern China.As everyone knows,aluminum toxicity in the acid soil is the main factor that restricts the growth of plants.In recent years,with the increasingly expanded acid-soil areas in the world,it has been one of the research hotspots to study how to reduce the aluminum toxicity of plants ecologically,conveniently and efficiently.At present,some existing studies show that to increase phosphorous concentration in soil can greatly alleviate symptoms of aluminum toxicity in plants and reduce or eliminate phytotoxicity efficiently,but specific mechanism has been not yet clearly.In order to conduct in-depth exploration on mechanism of relieving aluminum toxicity of plants,in this paper,2-year-old seedling of normal Camellia oleifera“Xianglin XCL15" was used as the test material to do a sand culture experiment.Influences of phosphorous on seedling growth of Camellia oleifera with aluminum toxicity,physiology and biochemistry were studied.Moreover,phosphorous in different phosphorous concentration was used to deeply analyze changes of root shoot ratio,root morphology,physiological property and root exudates components of Camellia oleifera seedling with aluminum toxicity.The main results of the study are shown as follows:(1)The study on different phosphorus levels on root shoot ratio and root morphologic changes of Camellia oleifera showed that root dry weight and root shoot ratio of Camellia oleifera were increased with the increase of phosphorus concentrations.With the increase of phosphorus concentrations,total length,root surface areas,root volume,root diameter,root branch numbers and root tip numbers of Camellia oleifera seedling with aluminum toxicity presented the rising trend.Overall length root surface area,root volume and root tip numbers of Camellia oleifera seedling with aluminum toxicity treated by 1.5mmol · L-1 were 2.72 times,11.51 times,2.43 times and 2.86 times of seedling treated by single aluminum toxicity,respectively,showing that overall length,root surface area and root diameter of Camellia oleifera seedling with aluminum toxicity reduced the inhibiting degree.Root differentiation of Camellia oleifera seedling was obviously reinforced and aluminum toxicity was relieved to some extent.(2)The sand culture study showed influences of different phosphorus on aluminum accumulation and nitrogen phosphorus and potassium contents of Camellia oleifera with aluminum toxicity.The study indicated that overground and underground aluminum contents of Camellia oleifera with aluminum toxicity were reduced by 15.84%?39.96%and 6.84%?61.05%,with the increase of phosphorus concentrations gradually.Overground total nitrogen contents of Camellia oleifera seedling with aluminum toxicity were increased by 0.75%-4.98%,total phosphorus contents were increased by 5.30%-8.61%,and total potassium contents were enhanced by 14.19%-42.59%,respectively after applying phosphorus,indicating that phosphorus could relieve persecution of aluminum toxicity on root tip,promote absorption of root nutrient elements,and decrease aluminum contents of plants.(3)The results of different phosphorus levels on root's physiological property influences of Camellia oleifera seedling with aluminum toxicity showed that with the increase of phosphorus concentrations,root exudates of Camellia oleifera seedling with aluminum toxicity and acid phosphatase(APA)activity of root tissues were reduced.Superoxide dismutase(SOD)was enhanced by 1.01-1.22 times,peroxidase(POD)activity was enhanced by 1.29-1.66times,and hydrogen peroxide(CAT)activity was enhanced by 1.16-1.63 times,showing that with the increase of phosphorus concentration,APA,SOD,POD and CAT activity of Camellia oleifera seelding with aluminum toxicity were obviously enhanced.(4)The measurement experiment of fluorescence parameters for Camellia oleifera seedling showed that threatened by aluminu,to applying phosphorus could reduce initial fluorescence(Fo),increase photochemical efficiency(PSII),increase electron transfer rate(ETR),decrease photoelectron(?PSII),,and lower NPQ,showing that phosphorus treatment enhanced maximal efficiency for solar energy utilization of seedling with aluminum toxicity,alleviated photoinhibition of plants with aluminum toxicity and would be good for plants to do photosynthesis.(5)GC-MS was used to do qualitative analysis of components in root exudates.Four root exudates of Camellia oleifera treated by phosphorus and aluminum included esters and alkane compounds.With the increase of phosphorus level,esters in root exudates of Camellia oleifera with aluminum toxicity presented the decreasing tendency.Triethyl citrate of root exudates had the highest relative contents,while relative contents of triethyl citrate was reduced gradually,indicating that phosphorus could promote root exudates to secrete more esters and alleviate harms of aluminum toxicity.In summary,the application of phosphorus can increase the total length of root system,root surface area and root tip number,and reduce the accumulation of aluminum in the whole plant,increase the nutrient content,decrease the activity of acid phosphatase,increase the activity of SOD and POD and CAT three kinds of stress-resistant enzyme activity,change the photosynthetic fluorescence parameters,so as to ease the toxicity of aluminum.