Effects Of Nitrogen And Phosphorus Addition On Growth And Physiology Of Camellia Oleifera Seedlings

Camellia oleifera Abel is an important woody oil species in south China.The nutritional status of seedling period determines the growth potential after afforestation.In production practice,reasonable fertilization can promote the growth of seedlings and improve the quality of seedlings.The acidic soil in the south of the main producing area of C·oleifera is generally deficient in phosphorus,and C·oleifera has adapted to the conditions of low phosphorus in the long-term evolution.Its demand for phosphorus may be different from that of other trees,especially under the conditions of different nitrogen nutrients,the demand for phosphorus is unclear.In this study,three main C·oleifera varieties CL4（CL4）,CL40（CL40）and CL53（CL53）in Jiangxi province were used as experimental materials to study the effect of phosphorus addition（P0:0 mmol·L-1,P1:0.4 mmol·L-1,P2:0.8 mmol·L-1,P3:1.6mmol·L-1）on the growth of C·oleifera seedlings under nitrogen application(N1:15mmol·L^-1)and no nitrogen application(N0:0 mmol·L^-1),to explore the utilization strategy of phosphorus nutrients in C·oleifera seedlings under different nitrogen levels,and further reveal the relationship between nitrogen and phosphorus nutrients in C·oleifera seedlings.The results can provide a reference for pot fertilization test and nutrient management of C·oleifera seedlings.The main results are as follows:（1）The response of growth index of C·oleifera to phosphorus level at seedling stage was significantly different due to substrate nitrogen nutrient level,plant growth time and variety.In the first year of fertilization,the plant height growth of CL4 and CL40 were increased by 30.58%and 3.37%,and the diameter growth were increased by 17.85%and 53.27%under the condition of no N application,but no P application or less P application was appropriate under the condition of N application.After two years of fertilization,P application had no significant effect on plant height growth.However,the ground diameter growth of CL4 and CL40 increased by 20.02%and19.17%respectively.Phosphorus application was detrimental to the plant height and ground diameter of CL53.The effect of P on root diameter and total root volume was small in the first year of fertilization.Under the condition of no N application,appropriate p application promoted the increase of total root length,total root surface area and total root volume for two consecutive years.Under the condition of N application,P application was not beneficial to the root growth of C·oleifera seedlings in the current year,but P（P3）level significantly promoted the root growth of CL4 and CL53 in the second year.（2）The response of C·oleifera biomass to P level at seedling stage was different with nitrogen level and variety.P application significantly increased the biomass of C·oleifera seedlings without N application.the biomass of CL4 and CL53 was increased by 51.81%and 60.26%in P1 and P2 treatments compared with P0treatment,and the biomass of CL40 was increased by 70.18%compared with P0treatment.However,too much P was not conducive to the biomass accumulation of C·oleifera seedlings under the condition of N application.And after two years of fertilization,no significant difference was found in the biomass increase of C·oleifera seedlings with or without nitrogen application.The effects of nitrogen and phosphorus supplementation on the root-shoot ratio in the first year were not significant.In the second year,moderate application of P fertilizer could increase the root-shoot ratio,but too much could decrease the root-shoot ratio.Nitrogen application reduced the proportion of root biomass and root shoot ratio.（3）Application of N and P can increase the green value and photosynthetic pigment content of C·oleifera seedlings.Regardless of whether N was applied,P could significantly improve the green value and photosynthetic pigment content of C·oleifera seedlings,but the promoting effect of N was more obvious.Under the stress of low or high P,the content of osmotic regulation substances in the body increased,and the content of soluble sugar,soluble protein and malondialdehyde was generally low under P1 concentration,and the physiological state was better.Under the condition of no N application,the enzyme activities of SOD and POD were generally increased by P application to CL4 and CL40,while the activities of SOD and POD increased by 12.37%and 21.62%.The activity of ACP enzyme was stronger under the condition of no P application,but under the condition of n application,the activity of ACP enzyme was stressed to CL53.The activities of SOD,POD and ACP were increased by 5.72%,7.62%and 31.06%respectively.（4）P application promoted the uptake of N and P in C·oleifera seedlings.Regardless of N application or not,the content and accumulation of N and P in CL4under P3 treatment were generally higher,and the content and accumulation of P were increased by 7.34%,18.05%and 31.10%,45.32%,respectively,compared with that without P application..Under the condition of no nitrogen application,the content of Nitrogen and phosphorus in CL53 was higher under P0 treatment,and the accumulation of nitrogen and phosphorus was higher under P1 and P2 treatment,while the absorption of phosphorus was better under P3 treatment,reaching 8.27%and 27.75%respectively.Under the condition that CL40 is not applied with nitrogen,P0 and P1 treatments are beneficial to the absorption of nitrogen,while P3 treatment is beneficial to the absorption of phosphorus.Under the condition of nitrogen application,the application of phosphorus is generally beneficial to the absorption of nitrogen,but not conducive to the absorption of phosphorus.Secondly,in the absence of nitrogen application,the root nitrogen content and accumulation of CL40 in P3treatment were significantly lower than that in P0 treatment,and decreased by 12.33%and 33.42%respectively.The results showed that higher P concentration was not conducive to the absorption and accumulation of nitrogen in roots.（5）Principal component analysis showed that biomass,nitrogen and phosphorus accumulation,root architecture and nitrogen content at seedling stage could reflect the growth of C·oleifera.The three varieties all grew well under nitrogen application,but had different responses to P level.Regardless of nitrogen application,CL4 and CL40ranked the highest in P3 and P1 treatment,respectively.CL53 ranked the highest in P2 treatment without nitrogen application,and P3 treatment ranked the highest.In conclusion,nitrogen nutrition is more important than phosphorus at seedling stage,CL4 is more tolerant to high phosphorus,CL40 is more tolerant to low phosphorus,and the phosphorus adaptation ability of CL53 is related to nitrogen nutrition conditions.