【目的】探究不同浓度氮素处理对东京野茉莉(Styrax tonkinensis)苗木茎中木质素含量和木质素合成关键酶活性的影响,为通过施加氮素提高东京野茉莉木材的造纸性能提供理论和实践依据。【方法】以3年生东京野茉莉实生苗为材料,分别在6月15日、7月5日、7月25日下午施氮肥,每次施肥设置5个不同用量的氮素处理:CK(0 g/株)、N1(1.5 g/株)、N2(3.0 g/株)、N3(6.0 g/株)、N4(9.0 g/株)等,并于6月15日(施肥前)、7月15日、8月15日、9月15日取样,测定苗木茎中木质素含量、木质素单体组成(G型,愈创木基木质素;S型,紫丁香基木质素;H型,对-羟基苯基木质素)以及木质素合成关键酶(PAL、POD、CAD、C4H)活性。【结果】东京野茉莉苗木茎中木质素含量随处理时间呈先降后升的趋势。在7月15日和8月15日,N1处理显著提高苗木茎中木质素含量,而N2、N3、N4处理下的木质素含量较CK低且一直保持较低水平。G型和S型木质素单体含量随氮肥用量增加整体呈现先上升后下降的趋势,氮素对H型木质素单体含量的影响无明显规律。7月15日,N1、N2处理下的S/G值(S型和G型木质素单体摩尔比)更高。在一定范围内,低浓度氮肥处理能够提高木质素合成关键酶如苯丙氨酸解氨酶(PAL)、过氧化物酶(POD)、肉桂酸脱氢酶(CAD)、反式肉桂酸-4-单氧化酶(C4H)活性,高浓度则会抑制酶活性。相关性分析发现, 7月15日,东京野茉莉苗木茎中木质素含量与POD活性呈显著正相关(P<0.05),与CAD、C4H、PAL活性呈负相关;在后续3个取样时期,POD活性与木质素含量保持正相关或极显著正相关;在7月15日和8月15日,S/G值与G型木质素单体含量显著负相关,与S型单体含量显著正相关。【结论】在东京野茉莉速生期增施氮肥可以降低木质素合成关键酶的活性,减少木质素的合成与积累。在东京野茉莉苗木速生前期施加N2用量(3.0 g/株)氮素,能在降低茎中木质素含量的同时使木质素S/G值升高,提高其造纸性能。

【Objective】This study investigated the effects of different nitrogen (N) fertilizer concentrations on lignin content and the activities of key enzymes involved in lignin biosynthesis in the stems of Styrax tonkinensis seedlings. This study aims to provide a theoretical and practical basis for improving the papermaking quality of S. tonkinensis wood through nitrogen management.【Method】Three-year-old S. tonkinensis seedlings were subjected to five N application concentrations: 0 (CK), 1.5 (N1), 3.0 (N2), 6.0 (N3), and 9.0 (N4) g per plant. Fertilizer was applied on the afternoons of June 15, July 5, and July 25. Stem samples were collected on June 15 (pre-treatment), July 15, August 15, and September 15 to determine lignin content, lignin monomer composition (G, S, H types), and the activities of key lignin biosynthesis enzymes.【Result】The lignin content in the stems showed an initial decrease followed by an increase over time. On July 15 and August 15, the N1 treatment significantly increased lignin content, whereas the N2, N3 and N4 treatments resulted in lower content than that of the CK and maintained consistently low levels. The contents of G-and S-type lignin monomers generally increased then decreased with rising N concentration, while H-type monomer content showed no clear trend. The S/G ratio was higher under the N1 and N2 treatments on July 15. Within a certain range, low N concentrations enhanced the activities of phenylalanine ammonia-lyase (PAL), peroxidase (POD), cinnamic acid dehydrogenase (CAD), and trans-cinnamic acid-4-monooxygenase (C4H), whereas high concentrations suppressed them. Correlation analysis revealed a significant positive correlation between lignin content and POD activity on July 15 (P < 0.05), and negative correlations with CAD, C4H and PAL activities. During the last three sampling dates, POD activity remained positively or highly significantly positively correlated with lignin content. On July 15 and August 15, the S/G ratio showed a significant negative correlation with G-type monomers and a significant positive correlation with S-type monomers.【Conclusion】Increased nitrogen application during the fast-growing stage of S. tonkinensis reduce the activities of key lignin biosynthesis enzymes and decrease lignin synthesis and accumulation. Applying N at the N2 concentration (3.0 g/plant) in the early fast-growing stage reduces lignin content of stems while increasing the S/G ratio, thereby improving papermaking performance.