Abstract:

As one of the important factors affecting forest soil organic carbon stocks, the effects of understory vegetation types on soil organic carbon and its components were explored to provide a theoretical basis for understory vegetation management and sustainable management in plantation forests. In order to determine the characteristics of soil organic carbon and its components under different understory vegetation types in Subtropical Cunninghamia lanceolata plantation, Indocalamus tessellatus (It), Diplazium donianum (Dd) and Oreocnide frutescenssp (Of) were taken as research objects. The mass fractions of total organic carbon (TOC), recalcitrant organic carbon (ROC), readily oxidizable organic carbon (ROOC), microbial biomass carbon (MBC) and dissolved organic carbon (DOC) in each soil layer at 0-10, 10-20, 20-40, 40-60 and 60-80 cm were measured, and the change characteristics of soil organic carbon components were also studied. The results showed that (1) soil TOC, ROC, and MBC mass fractions of all three understory vegetation types showed significant decreasing trends with deepening of the soil layer. The mass fraction of easily oxidized organic carbon was highest in the 0?10 cm soil layer. The mass fraction of DOC showed an increasing and then decreasing distribution trend in the whole soil profile. (2) The mass fraction of total soil organic carbon was significantly higher in the 40-60 cm soil layer for It (8.94 g?kg^?1) than that for Dd (7.00 g?kg^?1). The highest mass fractions of ROC in 0-10 cm soil layer and 10-20 cm soil layers were for Of (18.66 g?kg^?1) and Dd (11.38 g?kg^?1), respectively. The highest percentage of microbial biomass carbon in the subsurface soil of It community was 2.35%. (3) Pearson analysis showed that both soil active and recalcitrant organic carbons were positively correlated with TN, C/N ratio, DTN, and MBN (P<0.01). There were strong correlations between soil organic carbon components, and they all showed significant positive correlations with TOC (P<0.01). (4) RDA analysis showed that soil MBN (E=47.9%, 53.1%) explained each organic carbon component at significant levels in the two soil layers of 10?20 and 20-40 cm, and the environmental factors with the highest explanation in the 40?60 cm soil layer were TN (E=43.6%). The understory vegetation type mainly significantly affected the surface soil organic carbon components, and ROC differed more significantly among understory vegetation types. Of and Dd were more capable of promoting the accumulation of stable carbon in the surface soil, while the surface soil organic carbon fraction under It cover had a faster decomposition conversion rate.

Key words: Cunninghamia lanceolata plantation, understory vegetation, active organic carbon, recalcitrant organic carbon, soil profile

摘要：

林下植被作为影响森林土壤有机碳储量的重要因子之一，探讨其类型对土壤有机碳组分的影响，以期为人工林林下植被管理及可持续经营提供理论依据。以杉木（Cunninghamia lanceolata）人工林3种林下优势植被——箬竹（Indocalamus tessellatus）、双盖蕨（Diplazium donianum）和紫麻（Oreocnide frutescens）为对象，测定不同土层（0—10、10—20、20—40、40—60、60—80 cm）土壤总有机碳、惰性有机碳、易氧化有机碳、微生物生物量碳和可溶性有机碳的质量分数特征，分析各有机碳组分在林下植被、土层间的差异性。结果表明，（1）3种林下植被土壤总有机碳、惰性有机碳和微生物生物量碳的质量分数沿剖面均呈显著下降趋势，易氧化有机碳在0—10 cm土层均值最高，可溶性有机碳表现出先增后降的分布特征。（2）总有机碳在40—60 cm土层表现为箬竹（8.94 g?kg^?1）显著高于双盖蕨（7.00 g?kg^?1）；0—10、10—20 cm土层惰性有机碳质量分数最高的分别是紫麻（18.66 g?kg^?1）和双盖蕨（11.38 g?kg^?1）；箬竹表层土壤微生物生物量碳占比最高（2.35%）。（3）相关性分析表明，土壤有机碳组分均与全氮、C/N值、可溶性总氮以及微生物生物量氮呈极显著正相关（P<0.01）；各有机碳组分两两之间均呈极显著正相关关系（P<0.01）。（4）RDA分析表明，10—20、20—40 cm土层对各有机碳组分影响最显著的环境因子是微生物生物量氮（E=47.9%、53.1%），而在40—60 cm土层中影响最显著的是全氮（E=43.6%）。林下植被类型主要显著影响表层土壤有机碳组分，惰性有机碳在林下植被类型间的差异更显著。紫麻和双盖蕨能促进表层土壤稳定性碳的积累，而箬竹覆盖下的表层土壤有机碳组分具有较快的分解转化速率。

关键词: 杉木人工林, 林下植被, 活性有机碳, 惰性有机碳, 土壤剖面