天然次生林人工管理后土壤团聚体稳定性及碳氮分布变化

Changes of soil aggregate stability and carbon-nitrogen distribution after artificial management of natural secondary forests

【目的】探究次生林转变为红松人工林后土壤结构稳定性及有机碳、氮含量的变化,分析不同阔叶树种与红松混交能否缓解单一营造红松纯林所引起的地力下降,为混交树种的选择和林地土壤质量的精准提升提供依据。【方法】以东北林业大学帽儿山林场胡桃楸红松林、水曲柳红松林、黄檗红松林和红松纯林为研究对象,以胡桃楸和水曲柳为主要组成树种的次生林为对照,采用干筛与湿筛相结合的方法进行土壤团聚体分级,测定各粒径团聚体分布及碳氮含量,通过计算土壤结构稳定性参数及各粒径团聚体有机碳、氮贡献率,分析天然次生林转化成红松人工林后土壤团聚体稳定性及碳氮分布情况的变化。【结果】次生林转变为红松人工林后>2 mm粒径团聚体质量分数减少,其中胡桃楸红松混交林减少程度最低,为17.94%,<0.053 mm粒径团聚体质量分数增多,红松纯林增加程度最高,为45.78%;土壤的平均质量直径和几何平均直径降低,团聚体稳定性下降;各粒径团聚体有机碳、全氮含量均出现不同程度的下降,且胡桃楸红松林下降程度最低;次生林与3种红松混交林土壤团聚体有机碳、氮贡献率多以大团聚体为主,而红松纯林在10~20 cm和20~30 cm土层土壤团聚体有机碳、氮贡献率均以微团聚体为主。【结论】次生林转变为红松人工林后土壤团聚体稳定性和碳氮含量出现了不同程度的降低,从土壤团聚体分布、稳定性和有机碳、氮含量方面分析,胡桃楸、水曲柳和黄檗均为红松人工林适宜混交树种,3树种皆可促进红松人工林林地营养质量的提升。

[Objective]Exploring the stability of soil structure and the changes of organic carbon-nitrogen content after the conversion of secondary forest into Pinus koraiensis plantation,and analyzing whether the mixing of different broadleaved tree species with P.koraiensis could alleviate the decline of soil fertility caused by the pure P.koraiensis plantation,so as to provide a basis for the selection of mixed tree species and the targeted improvement of forest soil quality.[Method]Taking Juglans mandshurica-P.koraiensis plantation,Fraxinus mandshurica-P.koraiensis plantation,Phellodendron amurensis-P.koraiensis plantation and the pure P.koraiensis plantation built in Maoershan Forest Farm of Northeast Forestry University as the research object,and taking the secondary forest with main tree species of J.mandshurica and F.mandshurica as the reference,the soil aggregate classification was carried out by the combination of dry screening and wet screening,and the aggregate distribution,carbon-nitrogen content of each particle size were measured.Changes on soil aggregate stability and carbon-nitrogen distribution after the transformation of the secondary forest into P.koraiensis plantation were analyzed by calculating the parameters on stability of soil structure and the contribution rates of organic carbon-nitrogen in the aggregates with different particle sizes.[Result]After the secondary forest being transformed into P.koraiensis plantation,the mass fraction of>2 mm particle size aggregates decreased,among which J.mandshurica-P.koraiensis plantation decreased by 17.94%,the mass fraction of<0.053 mm particle size aggregates increased,and the pure P.koraiensis plantation increased by 45.78%.MWD and GMD of the soil decreased,and the stability of aggregates decreased.The contents of organic carbon and total nitrogen of aggregates with different particle sizes decreased in varying degrees,and the decline degree of J.mandshurica-P.koraiensis plantation was the lowest;the contribution rates of organic carbon and nitrogen in soil aggregates of the secondary forest and three mixed P.koraiensis plantations were mostly large aggregates,while the contribution rates of organic carbon and nitrogen in soil aggregates of the pure P.koraiensis plantation were mainly micro aggregates in 10−20 cm and 20−30 cm soil layers.[Conclusion]After secondary forest being transformed into P.koraiensis plantations,the soil aggregate stability,carbon and nitrogen content decrease in varying degrees.From the analysis of soil aggregate distribution,stability and organic carbon-nitrogen content,J.mandshurica,F.mandshurica and P.amurense are the suitable mixed tree species,which could improve the nutritional status of P.koraiensis plantation.