Effects Of Different Phosphorus Supply Levels On Root Growth And Physiological Characteristics Of Paper Mulberry Seedlings

Phosphorus is one of the essential nutrient elements in the process of plant growth and development.Most soils in South China,especially in Southwest China,are deficient in phosphorus,which affects plant growth and development.Broussonetia papyrifera(Paper mulberry)is a plant of the genus Morus,widely distributed throughout our country,with strong resistance to adversity,high feed value,and good ecological effects.It is an important pillar for the adjustment of agricultural structure and ecological control of rocky desertification in Guizhou.Exploring the effects of different phosphorus supply conditions on the growth and root morphology of paper mulberry and understanding the adaptation mechanism of paper mulberry to phosphorus stress is of great significance to the management and growth of phosphorus nutrients of plants in low-phosphorus soil areas in karst areas.This experiment uses a pot experiment with six levels of phosphorus supply,counted as P₀ and P₁(low phosphorus treatment),P₂and P₃(medium phosphorus treatment),P₄ and P₅(high phosphorus treatment).To study the changes of paper mulberry root system growth and physiological characteristics under different phosphorus supply levels.The main results are as follows:1.Low phosphorus levels will reduce the plant height,biomass,and leaf length and width of paper mulberry seedlings,and this trend becomes more apparent over time.With the increase of phosphorus supply level,soil available phosphorus concentration and phosphorus content in the aboveground and underground parts of plants,the plant height,biomass,leaf length and leaf width of paper mulberry seedlings increased first and then decreased,it is the highest under moderate phosphorus level.It shows that applying phosphorus is beneficial to the growth of paper mulberry seedlings,but not as much as possible.High phosphorus levels will also inhibit the growth of paper mulberry seedlings.2.The low phosphorus level leads to the decrease of the root length,root surface area and root volume of the paper mulberry root system.Unlike other plants,it does not show an increasing trend to the low-phosphorus environment.With the increase of the phosphorus supply level,the root characteristics and growth status of paper mulberry seedlings showed a synchronous change pattern,both increased first and then decreased,indicating that the available phosphorus in the growth environment where the paper mulberry is higher or lower than its own needs,will inhibit the growth of its root system.3.Correlation analysis of phosphorus accumulation with the morphology and root index of paper mulberry seedlings showed that the root morphology of paper mulberry seedlings and their internal phosphorus accumulation are mostly positively correlated(P<0.01),indicating that the root characteristics can be compared as an important reference index for judging the role of paper mulberry in the utilization of phosphorus in the future.4.Low phosphorus level will reduce the activity of protective enzyme of paper mulberry.With the increase of phosphorus supply level,the activity of protective enzyme will also increase,and the later performance tends to be stable.The activities of superoxide dismutase(SOD)and peroxidase(POD)will decreased under high phosphorus level.Low phosphorus level increased the content of malondialdehyde(MDA),but it gradually decreased with the increase of phosphorus supply level.The results showed that the activities of antioxidant enzymes in seedlings of paper mulberry co-operated with the phosphorus supply to maintain the plant growth,while the malondialdehyde decreased and controlled in a stable stage.5.The acid phosphatase(APA)activity of paper mulberry seedling leaves weakened under low-phosphorus conditions,and its APA activity also increased significantly with the increase of phosphorus supply levels,indicating that paper mulberry has a strong phosphorus transport ability;Significantly weakened under the conditions(P<0.05).It shows that the acid phosphatase activity of paper mulberry seedlings is affected by external phosphorus supply,and the reutilization capacity of paper mulberry seedlings is low at high phosphorus levels.6.Low phosphorus will promote the secretion of organic acids from the roots of paper mulberry seedlings,including malic acid,citric acid and fumaric acid,to weaken the effect of rhizosphere acidification.With the increase of phosphorus supply level,the amount of secreted organic acids continued to decrease.From high phosphorus(P₅)level to low phosphorus(P₀)level,the total amount of organic acids decreased by56.67%.It shows that paper mulberry is sensitive to the nutrient content in the soil and produces self-regulation to cope with the lack of phosphorus in the external environment.