亚热带不同林龄杉木林叶-根-土氮磷化学计量特征

以亚热带地区湖南会同5、10、15、20、25年生杉木(Cunninghamia lanceolata)人工林的针叶、细根及土壤(0—15、15—30、30—45 cm)为研究对象,在测定植物叶、细根、土壤中全N、全P含量的基础上,探讨杉木人工林全生命过程叶-根-土N、P化学计量特征的变化,为其经营过程提供基础数据。研究结果表明:(1)林龄对土壤N、P含量及N∶P具有极显著的影响(P0.01)。土层对土壤N含量影响显著(P0.01)。各层土壤N、P含量随林龄呈先减后升的趋势,变化显著(P0.05),土壤N、P含量的最大值分别出现在成熟林、幼龄林阶段,最小值出现在中龄林阶段。土壤N∶P随林龄呈增加趋势,但变化不显著。(2)林龄、器官均对植物N、P含量及N∶P具有极显著的影响(P0.01)。叶和细根的N、P含量随林龄呈"V"字型的变化趋势,且变化显著(P0.05),叶和细根N、P含量的最大值均出现在幼龄林、成熟林阶段,最小值出现在中龄林阶段。杉木叶的N∶P随林龄无显著变化,细根的N∶P随林龄显著增加(P0.05),杉木叶和细根N∶P变化范围分别为11.79—14.86,9.00—22.89。(3)5个林龄杉木叶、细根、土的N、P含量均表现为叶细根土,且差异显著(P0.05)。叶与细根的N、P含量及N∶P均显著正相关(P0.05)。0—15 cm土壤N与植物叶、细根N无显著相关性,15—30、30—45 cm土壤N与植物叶、细根N在5、10年生时存在显著相关性(P0.05)。5个林龄杉木叶、细根、土壤之间的P含量及N∶P均存在显著相关性。这些结果说明:在杉木的生长过程中,植物叶、细根以及土壤中养分不断变化,叶、细根、土之间的N、P化学计量特征显示出一定的相关关系。

Variation in the N and P stoichiometry of leaf-root-soil during stand development in a Cunninghamia lanceolata plantation in subtropical China

We measured total N and P concentrations of leaf, fine root, and soil (0-15, 15-30, 30-45 cm) in 5-, 10-, 15-, 20-, and 25-year-old Cunninghamia lanceolata plantations in Huitong, Hunan Province. The objective of this study was to determine the variation in the N and P stoichiometry of leaf-root-soil during the whole life process of Cunninghamia lanceolata plantations, and provide basic data to guide the management of Cunninghamia lanceolata plantations. The following results were obtained. (1) Stand age had a significant influence on soil N and P concentrations and the N:P ratio (P < 0.01). Soil layer only had significant influence on soil N concentrations (P < 0.01). Soil N concentrations decreased with increasing soil depth, whereas soil P concentrations and the N:P ratio showed no significant difference with increasing soil depth. In each soil layer, N and P concentrations initially decreased and then increased significantly with increasing stand age (P < 0.05). Soil N and P concentrations were the highest in 25-year and 5-year Cunninghamia lanceolata plantations, respectively, and were the lowest in 10-year and 15-year Cunninghamia lanceolata plantations. The soil N:P ratio increased with increasing stand age, although not significantly. (2) Stand age and organ type had a significant influence on plant N and P concentrations and the N:P ratio (P < 0.01). Leaf and fine root N and P concentrations showed a significant "V-shaped" pattern with increasing stand age (P < 0.05), whereas fine root P decreased slightly in 20-year Cunninghamia lanceolata plantations. Leaf and fine root N and P concentrations were the lowest in 15-year Cunninghamia lanceolata plantations, and were the highest in 5-year and 25-year Cunninghamia lanceolata plantations, respectively. The leaf N:P ratio did not change significantly with increasing stand age. The range of leaf N:P ratios was 11.79 to 14.86. For all stand ages, leaf N:P ratios were lower than 14, except for 20-year Cunninghamia lanceolata plantations, indicating that N was the main factor limiting the growth of Cunninghamia lanceolata. The fine root N:P ratio increased significantly with increasing stand age (P < 0.05), and the range of fine root N:P ratios was 9.00 to 22.89. (3) During the whole life process of Cunninghamia lanceolata plantations, N and P concentrations were significantly different between leaf, fine root, and soil in the order leaf > fine root > soil (P < 0.05). There were significant correlations between leaf and fine root N and P stoichiometry (P < 0.05), except for the leaf and fine root N of 25-year Cunninghamia lanceolata plantations. However, no significant correlations between 0-15 cm soil and leaf and fine root N concentrations were found. There were significant correlations between 15-30 and 30-45 cm soil and leaf and fine root N and P concentrations in 5-year and 10-year Cunninghamia lanceolata plantations (P < 0.05), whereas there were no significant correlations between soil and leaf and fine root N and P concentrations in 15-, 20-, and 25-year-old Cunninghamia lanceolata plantations. During the whole life process of Cunninghamia lanceolata plantations, there were significant correlations between leaf and fine root and soil P concentrations and the N:P ratio. It was concluded that with forest development, there have been changes in the nutrients of leaf, fine root, and soil, which reflect the strong links between leaf, fine root, and soil N and P stoichiometry.