桂西北杉木人工林养分积累及年净积累量变化

Nutrient accumulation and annual net accumulation changes of Cunninghamia lanceolata plantations in Northwest Guangxi

[目的]探究桂西北不同林龄杉木人工林养分积累及其年净积累量的变化过程,为杉木人工林丰产经营管理提供依据。[方法]以广西南丹县杉木人工林为研究对象,通过测定不同林龄(5、10、15和20年生)杉木人工林不同组分5种养分元素(N、P、K、Ca和Mg)含量,对不同林龄杉木人工林养分积累量、年净积累量及其分配特征进行了研究。[结果](1)不同养分元素在乔木层中平均含量均以N最高,其次是Ca或K,P或Mg最低;各养分元素在不同器官的含量存在差异且随林龄变化而变化。(2)5、10、15和20年生杉木人工林养分积累量分别为275.33、469.12、654.64和782.56 kg·hm^(-2),其中乔木层分别占76.34%、87.24%、89.93%和87.80%,灌草层分别占15.44%、6.19%、2.87%和4.14%,凋落物层分别占8.22%、6.57%、7.20%和8.06%,均随林龄增加而增加。(3)乔木层中各器官养分积累量的分配比例随林龄的增长发生变化,树叶占比随林龄增长而逐渐下降,干材和树皮占比则表现出相反的变化趋势。(4)4个林龄杉木人工林养分年净积累量依次为42.03、40.93、39.65和34.35 kg·hm^(-2)·a^(-1),随林龄的增加而减少,不同养分元素年净积累量以N最高,其次是K或Ca,P或Mg最低。杉木人工林每积累1 t干物质所需5种养分元素总量在4.51~10.99 kg之间,随林龄增加而减少。[结论]桂西北杉木人工林乔木层养分积累量随林龄增加而增大,不同林龄间养分积累量增长量为:5~10年生(199.08 kg·hm^(-2))>10~15年生(177.48 kg·hm^(-2))>15~20年生(99.36 kg·hm^(-2))。因此,应根据杉木人工林不同林龄阶段对养分元素的需求,结合林地土壤养分状况进行林地土壤养分管理。

[Purpose]Acquiring the nutrient accumulation and annual net accumulation dynamics of Cunninghamia lanceolata plantations will provide a scientific basis for the management of high-yield plantation in northwest Guangxi.[Method]Nutrient accumulation,annual net accumulation and distribution characteristics of C.lanceolata plantations in Nandan County of Guangxi Province were analyzed based on the contents of 5 nutrient elements[nitrogen(N),phosphorus(P),potassium(K),calcium(Ca)and magnesium(Mg)]of various organs and tissues.The plantations had been cultivated for 5,10,15 and 20 years,respectively.[Result](1)The content N was the highest among all the nutrient elements,which was followed by Ca and K,and the contents of P and Mg were the lowest.The nutrient contents varied among organs and stand ages.(2)Biomass accumulations reached 275.33,469.12,654.64 and 782.56 kg·hm^(-2) in 5,10,15,and 20-year-old plantations,respectively,with tree layer accounting for 76.34%,87.24%,89.93% and 87.80% of the accumulations,respectively;shrub and herb layers made up 15.44%,6.19%,2.87% and 4.14%of the nutrients accumulated,respectively,and litter layers accounted for 8.22%,6.57%,7.20% and 8.06% of the total.(3)The distribution pattern of nutrients in various parts of arbor layer changed with the growth of stand age.The proportion of nutrient allocated to leaves gradually decreased and the ratios of stem and bark followed the opposite trend.(4)Annual net nutrient accumulations reached 42.03,40.93,39.65 and 34.35 kg·hm^(-2)·a^(-1) in the C.lanceolata plantations at 4 stand ages,respectively.The annual net accumulation of N was the highest,which was followed by K,Ca,P,and Mg.And the plantations required 4.51-10.99 kg of the 5 types of nutrient elements for every 1 t of biomass accumulated.[Conclusion]The nutrients accumulation of tree layer increased with stand age in C.lanceolata plantation in northerwest Guangxi while the growths of nutrients accumulation followed a descending order,which was 199.08 kg·hm^(-2) for plantation under 5-10 years old,177.48 kg·hm^(-2) for plantation under 10-15 years old,and 99.36 kg·hm^(-2) for plantation under 15-20 years old.Therefore,age-specific soil nutrient management is recommended in view of different nutrient requirements among C.lanceolata plantation under different stand ages.