杉木人工林土壤氮矿化对长期氮添加和季节的响应

  目的  探讨长期氮沉降和季节变化对杉木Cunninghamia lanceolata人工林无机氮及氮素转化速率的影响。  方法  以福建省三明市沙县官庄国有林场亚热带人工杉木林为研究对象，开展长期(10 a)氮添加梯度(对照:N₀；低氮:N₁；中氮:N₂；高氮:N₃)野外控制试验，通过野外原位培养方法测定氮添加对净氮矿化、硝化和淋溶的影响。  结果  ①氮添加显著提高了铵态氮(NH₄ +-N)、硝态氮(NO₃ ?-N) 和总无机氮质量分数，从大到小均依次为N₃、N₂、N₁、N₀，且铵态氮质量分数均高于硝态氮。②氮素转化速率随氮添加梯度而增大，高氮显著促进了氮素转化(P＜0.05)。③季节显著影响氮素转化(P＜0.05)，净氮矿化速率、硝化速率与淋溶速率均表现为夏季高、冬季低的季节动态。  结论  氮添加显著增加了土壤无机氮与氮素转化速率，土壤pH、碳氮比(C/N)和土壤温度可能是研究区氮添加驱动氮素转化的主要因子。在杉木人工林的经营与管理中需要更多关注土壤养分和氮素转化速率对外源氮输入的响应。图2表3参40

Response of soil N mineralization to long-term N addition and season in Cunninghamia lanceolata plantation

  Objective  With an experiment conducted Guanzhuang National Forestry Farm, Sha County, Sanming City of Fujian Province, this study is aimed to investigate the effects of long-term nitrogen (N) deposition and seasonal change on inorganic N and N transformation rates in the Cunninghamia lanceolata plantation.   Method  Besides a long-term (10-year-long) N addition experiment with four gradients (control: N₀, low: N₁, medium: N₂, high: N₃), the cultivation experiment in situ was conducted to determinate the N mineralization, nitrification and leaching rates in response to N addition.  Result  (1) N addition significantly increased the mass fractions of ammonium N (NH₄ +-N), nitrate N (NO₃ ?-N) and total inorganic N, showing the trend of N₃, N₂, N₁ and N₀, and the ammonium N was higher than nitrate N. (2) N transformation rates increased with the N addition gradients, while high N addition significantly promoted the N transformation rates. (3) Seasonal changes significantly affected N transformation rates, and the N mineralization, nitrification and leaching rates were higher in summer and lower in winter.   Conclusion  N addition significantly increased soil inorganic N and N transformation rates whereas soil pH, C/N ratio and temperature may be the factors of N addition driving soil inorganic N and N transformation rates in the C. lanceolata plantation. Therefore, closer attention should be paid to the response of soil nutrients and N transformation rates to exogenous N input in the management of C. lanceolata plantation. Ch, 2 fig. 3 tab. 40 ref.]