短轮伐期毛白杨不同密度林分土壤有机碳和全氮动态

采用裂区试验设计,于2005—2008年连续4年测定了不同造林密度(2 m×2 m、2 m×3 m、2 m×3.5 m、2 m×4 m、2 m×5 m、3 m×3 m、3 m×4 m)下2年生三倍体毛白杨(B304)和对照二倍体(1319)人工林土壤有机碳和全氮含量,以明确不同密度林分土壤有机碳和全氮动态变化规律及其相关性。结果表明:(1)受造林密度、生长时间及其交互作用的显著影响,4年生长期内林地土壤有机碳含量呈先降后升的变化特点。其中,2008年B304在2 m×3 m造林密度下土壤有机碳含量显著高于其它年份,说明此造林密度有利于发挥三倍体毛白杨林土壤固碳的生态功能。(2)4年生长期内,土壤全N含量受生长时间及其与造林密度的交互作用的显著影响。在3 m×3 m造林密度下,二倍体毛白杨林地土壤全N含量逐年降低,而三倍体毛白杨2007年的土壤全N含量显著增加,该造林密度利于三倍体毛白杨林地土壤N的积累。(3)土壤有机碳/全氮比值变化与有机碳含量变化规律一致,且均在2006年达到最低值。(4)在2008年,三倍体毛白杨在2 m×3 m和2 m×3.5 m造林密度下土壤有机碳与全N含量呈现显著正相关关系,而2 m×5 m造林密度下的二倍体毛白杨林地呈显著性负相关关系,体现了毛白杨林地土壤有机碳与全N含量复杂的相关性。

Dynamics of soil organic carbon and total nitrogen contents in short-rotation triploid Populus tomentosa plantations

The dynamics of soil organic carbon (C) and total nitrogen (N) contents were investigated in the triploid (vs. B304) and the control diploid (vs. 1319) Populus tomentosa plantations from 2005 to 2008. The experiment was a split plot design with seven planting densities (2 m×2 m, 2 m×3 m, 2 m×3.5 m, 2 m×4 m, 2 m×5 m, 3 m×3 m and 3 m×4 m). The following results were obtained: (1) Planting density, sampling year and their interactions had significant effects on soil organic C content. The organic C decreased in 2006 and then increased during the following years, and the maximum content was found in the 2 m×3 m plantation of triploid P. tomentosa in 2008. So this planting density was optional for the triploid clone to enhance the C sequestration. (2) Significant effects of sampling year and its interactions with planting density on soil total N were found during the 4-year growing period. In the 3 m×3 m plantations, the soil total N content decreased for the control diploid clone with the growth of the tree, and increased for the triploid clone in 2007 compared with the former years. The results suggested the planting density of 3 m×3 m was optional for the triploid clone to return the N element into plantation soil. (3) The dynamics of the ratio of soil organic C to total N was in accordance with the changes of the soil organic C. Both were lowest in 2006. (4) Significant positive correlations between soil organic C and total N were found in 2 m×3 m and 2 m×3.5 m growth densities in triploid P. tomentosa plantation in 2008. Significant negative correlation between soil organic C and total N was found in 2 m×5 m planting density for the control.