Effects Of Fertilization On The Growth Traits Of Phoebe Zhennan S. Lee In Pot And Soil Fertility

Phoebe zhennan S. Lee is a rare and unique species of Sichuan with natural distribution in Ya’an and Dujiangyan. But the causes of long-standing human deforestation, immature seedling cultivation technology and slow growth are seriously restricting the development process of P. zhennan plantation. The purpose of seedling fertilization is to constantly improve soil fertility on the basis of normal growth, in order to promote the sustained and rapid development of seedling production. At present, fertilization researches on trees are few, even more less on rare species seedlings, in addition, most previous studies individually from a single perspective to investigate the effects of fertilization on plant growth or soil environment, failed to analyze the the combined effects of fertilization on trees and soil fertility systematically.A pot experiment was conducted to study the effects of application of four fertilizers, nitrogen fertilizer (NF), compound fertilizer (CF), organic fertilizer (OF) and mixed fertilizer (MF), on 1-year-old P. zhennan seedlings. Each fertilizer was applied at three levels based on the annual nitrigen application rate, namely, low (L, 0.3 g/pot), medium (M,0.6 g/pot) and high (H,0.9 g/pot), with a control of no fertilization (CK). All fertilizers were divided into three equal parts and applied into pail in the middle of May, July and September, respectively, to explore the effects of fertilizer application on photosynthetic and growth characteristics of the seedlings, as well as the changes in soil environment after fertilization (repeat in 2014). Preliminary results are as follows:(1) Fertilization of P. zhennan seedlings on the growth characteristicsAfter the first year of fertilization, only CF showed a relatively weak effect on the growth of P. zhennan seedlings. NF acted well only in early stage (May-June). MF application reflected a relative lack of nutrient in the late phase (September-October). However, OF was able to provide nutrients for the seedlings continuously, with the greatest stimulation at medium application (MOF), which displaying an increment twice as much as that of CK. The second year of fertilization, application of CF significantly increased height and diameter growth. From the point of total growth amount of two years, OF and MF were better than NF and CF, while MOF showed consistently advantage.(2) Fertilization of P. zhennan seedlings on leaf mineral elements N, P, K contentThe first year, there were no promoting effects on N, P, K absorption of leaves after application of NF, but reducing the K content in the late phase (September-October). Application of OF significantly increased the nutrient content of leaves, but reduced P, K content to CK level in the early stage (May-June) under excessive amount level. Besides, uptake for P, K improved with amount of MF rised in the late phase. After the second year of fertilization, the advantages of medium application of organic fertilizer (MOF) were quite obvious, which K content was two times more of CK.(3) Fertilization of P. zhennan seedlings on photosynthetic physiologyJudging from the fertilization effects of two years, application of all fertilizers promoted chlorophyll synthesis, extended the functional period of green leaves and enhanced net photosynthetic rate and gas exchange parameters of P. zhennan seedlings. While OF and MF performed more effectively than NF and CF, among which middle level of organic fertilizer (MOF) was most significant. Second year, CF significantly improved photosynthetic physiology of P. zhennan seedlings.(4) Fertilization of P. zhennan seedlings on soil nutrient contentThe first year’s results showed that, NF slightly promoted the hydrolysis nitrogen and available potassium content in soil, while CF only affected available potassium. OF performed most efficient, especially middle level (MOF), with soil nutrient content significantly improved. After MF application, soil nutrient status improved significantly, but poorer than OF. Second year, MOF still performed fullest, with phosphorus content more than two times of CK.(5) Fertilization of P. zhennan seedlings on microbial biomass carbon and nitrogenDuring the first year of fertilization, NF and CF hardly affected soil microbial biomass C (MBC) and N (MBN). OF could continue increasing MBC and MBN, with the maximum promotion under middle level (MOF).In the late phase of MF application (September-October), MBC and MBN increased significantly, without differences in MBC among three levels, while MBN increased as fertilization levels increasing. Second year, MBC and MBN increased nearly 1-fold and 2-fold relative to CK under MOF treatment.(6) Fertilization of P. zhennan seedlings on soil enzyme activityIn the study, NF and CF application on soil enzyme activity were not affected in the late of first year (September-October), but MF significantly improved soil activity. OF apparently increased soil enzyme activity with best effect under middle level (MOF), but excessive amount (HOF) caused sucrase activity plunged to CK level. Second year, NF and CF still showed little help, while sucrase activity reached eight times of CK after application of OF.(7) The correlation analysis of growth indices and main soil fertility indicesThe correlation analysis of growth indices and main soil fertility indices showed that soil sucrase activity and microbial biomass N could reflect P. zhennan growth conditions effectively.Overall, in seeking to promote growth of P. zhennan seedlings after fertilization, meanwhile maintain and improve soil fertility as much as possible, middle level of organic fertilizer (MOF) was the first choice undoubtedly. In addition, due to the combined application of organic fertilizer based on NF, MF not only improved soil fertility, but also promoted the growth of P. zhennan seedlings significantly, which could be used as a timely and effective improvement measures during fertilization process.