Study On Growth And Nutrient Requirement Of Phoebe Zhennan In Seedling Stage

Phoebe zhennan is a rare species unique to China and a high-quality timber and economic tree species in China.The tree is popular for its beautiful crown shape and evergreen nature,and is widely used for gardening and landscape decoration.However,the slow growth and development of the seedlings,the high requirements for site conditions,and the lack of a suitable living environment have become important factors limiting the cultivation of seedling resources and high-quality development of Phoebe zhennan.In order to understand the growth and nutrient requirements of Phoebe zhennan seedlings and to achieve the growth regulation and efficient cultivation management of Phoebe zhennan seedlings,this study took one-year Phoebe zhennan seedlings as the research object to carry out the research on the growth and nutrient requirement law and the DRIS nutrient diagnosis of Phoebe zhennan seedlings to reveal the growth and development patterns,photosynthetic parameters and chlorophyll content changes,dry matter accumulation and distribution,and nutrient requirements of Phoebe zhennan seedlings.The study also investigated the effects of different light intensities on the growth of Phoebe zhennan seedlings,and screened out the light intensity suitable for the growth of seedlings in order to provide a theoretical basis for guiding the growth control of Phoebe zhennan seedlings.The main findings are as follows:（1）The net photosynthetic rate（Pn）of Phoebe zhennan seedlings peaked in July and was lowest in January,showing a"single-peaked"variation throughout the year.The variation pattern of stomatal conductance（Gs）and transpiration rate（Ci）was consistent with that of Pn,while the annual variation trend of intercellular CO₂ concentration（Ci）showed a"bimodal"phenomenon,with the highest concentration in July and the second highest in January.The annual variation of chlorophyll content in seedlings of Phoebe zhennan ranged from 35.1 to 39.5,with chlorophyll content gradually decreasing from September to December and reaching a minimum in January of the following year,but gradually increasing after March and reaching a maximum in July.（2）The growth of seedling height and diameter throughout the year showed a"slow-fast-slow"growth trend,with plant height slowing down in September-November,basically stagnating in December-February of the following year,growing vigorously in March-July,and slowing down in July-August due to extreme The growth was slow from July to August due to extreme weather conditions.The logistic model was used to fit the equations for the growth patterns of height and diameter of seedlings,and the coefficients of determination（R²）were 0.962 and 0.974,respectively,which were highly reliable;the growth of seedlings was divided into three periods:early growth,rapid growth,and late growth.The trend of dry matter accumulation and growth volume during the seedling stage of Phoebe zhennan was consistent,with dry matter accumulation gradually slowing down from September to December,basically stagnating from January to March,with peak accumulation from May to July,and rapidly decreasing from July to September.Except for January when the dry matter distribution ratio was root>stem>leaf,the contribution of leaf to the dry matter of the whole plant was the highest in all the periods.The root-to-crown ratio gradually increased from September to December,with the highest root-to-crown ratio in January and gradually decreased after February.（3）The order of mineral nutrient content in seedlings of Phoebe zhennan is N>K>P.The N,P and K contents are all enriched in March and September,and the mineral nutrients are distributed in a larger proportion in leaves and roots,but less in stems.Among them,the distribution of N and P contents among organs was:leaves>roots>stems,while the K content was:roots>leaves>stems.The order of magnitude of mineral nutrient accumulation in Phoebe zhennan seedlings was N>K>P.N and K elements accumulated the most in July to September and the least in January to March,while P elements accumulated the most in May to July and the least in March to May.The distribution of N accumulation among the organs was as follows:leaves>stems>roots,while P and K accumulation was as follows:leaves>roots>stems.（4）A ternary quadratic regression rotational fertilization design was used to fertilize Phoebe zhennan seedlings.The fertilization ratios had highly significant effects on the height,diameter and biomass of the seedlings,with N,P and K elements having the highest variation effects on the height and diameter of the seedlings in the order of N>K>P and on the biomass accumulation in the order of N>P>K.The highest value-added in the growth and net bioaccumulation of seedling height and ground diameter was observed in treatment 8(N0.81 g·pot^-1,P 0.71 g·pot^-1 and K 0.61 g·pot^-1).The quadratic regression equation for seedling biomass was also established for different fertilizer ratios,and the optimum fertilizer application rate and optimal solution were calculated.（5）Diagnosis and recommendation integrated system（DRIS）was used to diagnose the leaf nutrients of Phoebe zhennan at seedling stage under different proportions of fertilization.The optimal ratio range of nutrient contents of N,P and K in the leaves was obtained through the combination of DRIS graphic method and index method,which were as follows:P/N0.097～0.257,P/K 0.205～0.269,N/K 1.068～1.600.As a whole,Phoebe zhennan seedlings have the highest demand for K,followed by N and relatively less demand for P.（6）Compared with full light,shading significantly promoted the growth and development of Phoebe zhennan at seedling stage under different light intensity.When the light transmittance was 50.9%,the increase of plant height,ground diameter and biomass of Phoebe zhennan reached the maximum.Light intensity had a certain effect on the morphological plasticity of Phoebe zhennan at seedling stage.The leaf area and specific leaf weight increased first and then decreased with the decrease of light intensity,and reached the maximum under the condition of moderate light intensity.The root-shoot ratio decreased with the decrease of light intensity.（7）Different light intensities affected the light response curve,fluorescence parameters and chlorophyll content of Phoebe zhennan seedlings to different degrees.The light response curves of the appropriate shading treatments were significantly higher than those of the full-light and heavy shading treatments.In the light response curve,the apparent quantum efficiency（AQY）,maximum net photosynthetic rate（Pn max）and light saturation point（LSP）of Phoebe zhennan seedlings peaked at the treatment with 50.9%light transmittance,while light compensation point（LCP）and dark respiration rate（Rd）decreased with decreasing light intensity.Among the fluorescence parameters,Fv/Fm and Fv/Fo were higher in the shade treatment than in full light,andΦPSII,q P and ETR all increased significantly with decreasing light intensity,while NPQ changed in the opposite trend.At the same time,Phoebe zhennan seedlings also improved their light energy utilization by decreasing the ratio of antenna heat dissipation（D）and non-photochemical reaction dissipation（Ex）and increasing the ratio of photochemical reaction dissipation（P）.Chlorophyll a,b and total chlorophyll of Phoebe zhennan seedlings increased significantly with decreasing light intensity,while the values of chlorophyll a/b were opposite to the trend of chlorophyll content.（8）Under different light intensity levels,Phoebe zhennan seedlings absorbed the most mineral nutrients at medium light intensity levels,while the seedlings showed a significant inhibitory effect on N,P and K uptake under full light conditions,and mineral nutrients were enriched in leaves and roots to a higher extent.