Study On Root Morphology And Physiological Mechanism Of Phosphorus Efficient Utilization In Pitaya

Phosphorus is an essential element for crop growth and is involved in important physiological and biochemical processes in the body.The level of phosphorus supply to the crop directly affects the growth of the lower-ground root system and determines the yield and quality of the crop.Pitaya is an important cash crop in tropical and subtropical regions,and the high fruit phosphorus content and huge production make the demand for the phosphorus of pitaya extremely high.Therefore,it is important to clarify the phosphorus uptake characteristics of pitaya and the response of root morphology and physiological processes to environmental phosphorus content to fully exploit the plant’s biological potential and understand the process of efficient phosphorus resource uptake in pitaya.The main plant varieties of pitaya include red-skinned white flesh,red-skinned red flesh,thornless yellow dragon,and Ecuadorian hylocereus megalanthus.It has been shown that different varieties of plants have different sensitivity to phosphorus,and the root system will show different morphological and physiological processes in the process of efficient utilization of soil phosphorus resources,while the phosphorus uptake and utilization strategies of different pitaya varieties are not clear.To address the above background,this study was conducted to investigate the effects of phosphorus levels on root morphology and physiological processes by setting different phosphorus supply concentrations in a hydroponic experiment,and to investigate the variability of phosphorus resource utilization by different varieties of pitaya at high and low phosphorus levels in a soil culture experiment.The above studies help to reveal the inter-root processes of efficient utilization of phosphorus resources in pitaya and provide a theoretical basis for the rational application of phosphorus fertilizer to different varieties of pitaya in production.The main research progress and conclusions are as follows;In the hydroponic experiment,phosphorus supply did not affect aboveground biomass accumulation compared to no phosphorus application.The total root length and the number of fine roots ≤ 0.05 mm in diameter were significantly higher in the 0.1 mmol/L treatment than in the other treatments,and the number of thick roots ≥ 2 mm in diameter was higher in the 1.0 mmol/L phosphorus level than in the other treatments.(The 0.01mmol/L treatment had the highest total organic acid content and higher root cation exchange capacity(CEC)content;the organic acid secretion rate decreased and the root CEC content decreased at the 1.0 mmol/L phosphorus level compared with no phosphorus application.In terms of another nutrient uptake,the uptake concentration of Fe in the parent branch and primary lateral branches showed a gradual decrease with increasing phosphorus application.N,Ca,Mg,Mn,and Zn in the secondary lateral branches showed a significant negative correlation with the increase of phosphorus application.In the soil culture experiment: ’Softy Big Red’ had greater below-ground biomass and below-ground phosphorus accumulation,increased root crown ratio,total root length,and root surface area,enhanced inter-root acid phosphatase activity,and highest phosphorus utilization efficiency compared with other varieties at 10 mg/kg phosphorus supply level.’Thornless Yellow Dragon’ had higher aboveground biomass and superficial root length and the largest root surface area at 10 mg/kg phosphorus supply level,the highest belowground biomass and root crown ratio,the largest whole plant phosphorus accumulation,and significantly higher total root length and total root volume at 100 mg/kg phosphorus supply level compared with other varieties.’Vietnam No.1’ dragon fruit showed significantly higher aboveground biomass,expanded surface root proportion,highest phosphorus uptake efficiency,phosphorus root efficiency ratio and phosphorus transfer efficiency,and highest phosphorus accumulation in the whole plant at 10 mg/kg phosphorus supply level compared with among varieties,and the highest phosphorus root efficiency ratio,catalase activity,and phosphorus transfer efficiency under high phosphorus environment compared with among varieties.The overall growth and development of ’Bird’s Nest Fruit’ was poorer at 10 mg/kg phosphorus supply level than at 100 mg/kg phosphorus supply level,and the total root length,average root diameter,root surface area and total root volume were all increased.phosphorus environment was stronger.Meanwhile,for other nutrient uptake,Zn gradually decreased with the increase of phosphorus accumulation in most varieties,showing a significant negative correlation.In summary,this thesis demonstrated through different culture and research methods that moderate phosphorus supply(0.01 mmol/L or 0.1 mmol/L)promoted dragon fruit root growth as well as root organic acid secretion and ion uptake capacity,while excessive phosphorus supply(1.0 mmol/L)significantly inhibited root growth and also significantly reduced the uptake of intermediate and trace elements in above-ground branches.’Softy Big Red’ adapted to 10 mg/kg phosphorus supply level mainly through root morphology and mobilization changes in inter-root acidification and enzyme activity,’Thornless Yellow Dragon’ showed better adaptation in root morphology and phosphorus accumulation at 100mg/kg phosphorus supply level The root morphology as well as phosphorus accumulation of ’Vietnam No.1’ showed better adaptability at 100 mg/kg phosphorus supply level,’Vietnam No.1’ had higher phosphorus efficiency at 10 mg/kg phosphorus supply level,and was physiologically sensitive to 100 mg/kg phosphorus supply level,showing the toxic response of high phosphorus inhibition of plant growth.’Bird’s nest fruit’ showed some growth impairment at either 100 mg/kg phosphorus supply level or 10 mg/kg phosphorus supply level,requiring a higher range of suitable phosphorus concentration.