• ISSN 1008-505X
  • CN 11-3996/S

硝态氮抑制毛竹幼苗生长的生理机制：氮同化受阻与多元素协同失衡

Physiological mechanisms underlying nitrate-induced inhibition of rapid expansion in Moso bamboo (Phyllostachys edulis) seedlings: Impeded nitrogen assimilation and multi-element synergistic imbalance

    摘要
  • 摘要:
    目的 研究硝态氮处理对毛竹幼苗养分积累、光合效率以及氮代谢酶活性的影响，初步揭示其“厌硝”机理，为调控毛竹在生态林中的过度扩张提供养分管理措施。
    方法 以毛竹(Phyllostachys edulis)幼苗为试材，开展氮素形态差异和硝态氮供应时长蛭石盆栽试验。根施营养液中铵态氮和硝态氮分别为4 mmol/L (NH4)2SO4和8 mmol/L NaNO3，以不供氮处理作为对照(CK)。试验期间，连续监测毛竹幼苗地上部和地下部生长、养分积累量及硝酸还原酶(NR)活性，并测定叶片叶绿素含量(SPAD值)，分析幼苗生长、硝态氮含量及硝酸还原酶(NR)活性之间的关系。
    结果 硝态氮处理对毛竹幼苗生长促进作用不明显，叶绿素含量较CK显著降低52.94%。与铵态氮处理相比，硝态氮处理下幼苗苗高、SPAD值、叶片数、总生物量、根长及根表面积分别显著降低51.11%、87.40%、58.70%、91.01%、65.77%和79.96%。与CK相比，硝态氮处理毛竹幼苗叶片中P、Ca、Mg、S和Al元素含量分别显著增加50.53%、75.21%、12.49%、18.17%和21.36%，而N、K、Fe、Mn、Cu和Na元素含量分别降低2.98%、44.83%、18.40%、45.01%、17.13%和51.63%；根系中P、K、Mg含量分别显著增加13.23%、10.89%和13.92%，而S、Fe、Mn、Zn、Na和Al含量分别显著降低21.05%、52.59%、57.69%、35.95%、30.73%和51.79%。与铵态氮处理相比，硝态氮处理的毛竹幼苗叶片中P、Ca、Mg和S元素含量分别显著增加98.46%、51.23%、13.99%和26.70%，而N、K、Fe、Mn和Na元素含量分别显著降低5.00%、20.30%、29.58%、64.15%和16.01%；根系中P、K、Mg元素含量显著增加，增幅分别达40.87%、6.73%和44.62%，而N、S、Fe、Mn、Na和Al元素含量分别显著降低5.24%、18.30%、46.88%、81.62%、25.56%和34.10%。在试验0～42天内，硝态氮处理下苗高、叶片数、生物量及NR活性均有所增加，42天后开始降低。与初始(0 天)相比，28～98 天期间叶片和根系中硝态氮积累显著增加，增幅分别达146.89%～378.44%和232.62%～516.60%；而在42~98天内，NR活性显著下降，叶片和根系降幅分别为1.43%～87.96%和11.19%～89.39%，并伴随生物量下降及根冠比升高。
    结论 毛竹在长期进化过程中形成了“喜铵厌硝”的氮营养特性。持续供应硝态氮会导致幼苗体内硝态氮积累，显著抑制硝酸还原酶活性，进而影响氮素同化过程；同时，Fe、Mn、Zn等微量元素吸收受阻，叶绿素含量下降，最终抑制幼苗生长甚至导致生长停滞。因此，硝态氮供应可作为调控毛竹生长的潜在养分调控措施。

     

    Abstract:
    Objectives The effects of nitrogen supply forms and nitrate supply duration on nutrient uptake, photosynthetic efficiency, and nitrogen metabolism enzyme activity in Phyllostachys edulis (P. edulis) seedlings were studied to preliminary reveal nitrogen form preference and to provide nutrient management strategies for regulating the excessive expansion of P. edulis in ecological forests.
    Methods Pot experiments were conducted using P. edulis seedlings as test materials and vermiculite as growth substrates. Nitrogen treatments included 4 mmol/L (NH4)2SO4, 8 mmol/L NaNO3, and a no nitrogen control. Growth and nutrient accumulation in both aboveground and underground parts of P. edulis seedlings, nitrate reductase (NR) activity, and leaf chlorophyll content (SPAD) were measured. The relationships among seedling growth, nitrate nitrogen content, and nitrate reductase (NR) activity were analyzed.
    Results Compared with CK, nitrate treatments showed no significant promotion on seedling growth but significantly reduced chlorophyll content by 52.94%. Seedling height, SPAD values, leaf number, total biomass, root length and root surface area under nitrate treatment were significantly lower than those under ammonium treatments by 51.11%, 87.40%, 58.70%, 91.01%, 65.77% and 79.96%, respectively. Compared with CK, nitrate treatment significantly increased P, Ca, Mg, S, and Al content in P. edulis leaves by 50.53%, 75.21%, 12.49%, 18.17%, and 21.36%, respectively, while significantly decreasing N, K, Fe, Mn, Cu, and Na contents by 2.98%, 44.83%, 18.40%, 45.01%, 17.13%, and 51.63%, respectively. In roots, P, K, and Mg contents increased significantly by 13.23%, 10.89%, and 13.92%, respectively, whereas S, Fe, Mn, Zn, Na, and Al contents decreased significantly by 21.05%, 52.59%, 57.69%, 35.95%, 30.73%, and 51.79%, respectively. Compared with ammonium treatment, nitrate treatment significantly increased leaf P, Ca, Mg, and S contents by 98.46%, 51.23%, 13.99%, and 26.70%, respectively, while decreasing N, K, Fe, Mn, and Na contents by 5.00%, 20.30%, 29.58%, 64.15%, and 16.01%, respectively. In roots, P, K, and Mg contents increased significantly by 40.87%, 6.73%, and 44.62%, respectively, whereas N, S, Fe, Mn, Na, and Al contents decreased significantly by 5.24%, 18.30%, 46.88%, 81.62%, 25.56%, and 34.10%, respectively. During 0–42 days of nitrate treatment, seedling height, leaf number, biomass, and NR activity initially increased slightly and then declined. Compared with day 0, nitrate accumulation in leaves and roots significantly increased from day 28 to day 98, with increases of 146.89%–378.44% and 232.62%–516.60%, respectively. In contrast, NR activity sharply decreased by 1.43%–87.96% in leaves and 11.19%–89.39% in roots, accompanied by reduced biomass and an increased root-to-shoot ratio.
    Conclusions During long-term evolution, P. edulis has developed a characteristic nitrogen preference of “ammonium over nitrate”. Under continuous NO3− supply, the accumulation of nitrate nitrogen in P. edulis seedlings coincide with a significant decline in nitrate reductase activity. This impairs nitrogen assimilation, hinders the uptake and accumulation of essential micronutrients such as Fe, Mn, and Zn, and drastically reduces chlorophyll content. Consequently, seedling growth is severely restricted, often leading to growth arrest. Therefore, the regulation of NO3− supply can be utilized as an effective technical strategy for controlling the growth of moso bamboo.

     

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