马尾松林两种林下植被土壤碳氮特征及其与凋落物质量的关系

以飞播马尾松林为研究对象，通过典型样地调查和样品测定，采用配对样本t检验和冗余分析（RDA）方法分析芒萁类和禾草类两种林下植被类型土壤碳、氮特征及其与凋落物质量之间的关系。结果表明：（1）土壤有机碳、微生物量碳、可溶性有机碳、全氮、速效氮、微生物量氮和可溶性有机氮含量在0-10、10-20 cm土层均表现为禾草类显著高于芒萁类（P < 0.05），而在20-40、40-80 cm土层两种植被类型碳氮指标的大小未表现出相同的变化规律，且差异不显著（P > 0.05）。（2）两种植被类型凋落物半分解和未分解层的C含量及C/N值均表现为芒萁类显著高于禾草类（P < 0.05），而N含量则表现为禾草类显著高于芒萁类（P < 0.05）；同一植被类型的未分解层C含量及C/N值均显著大于半分解层，N含量则半分解层显著大于未分解层（P < 0.05）。（3）0-10 cm土层两种类型凋落物C/N值和C含量均与土壤碳氮各指标呈显著负相关（P < 0.05），N含量与土壤碳氮各指标的相关性不显著（P > 0.05）；10-20 cm土层，芒萁类的半分解层C/N值与土壤碳氮各指标存在显著相关性（P < 0.05），禾草类的凋落物C含量与土壤碳氮各指标也存在显著相关性（P < 0.01）。林下植被凋落物C/N值越小，其分解速率越快，有利于土壤养分的积累，禾草类凋落物C/N值低于芒萁类是导致其土壤碳氮指标高于芒萁类的重要原因。

Characteristics of soil carbon and nitrogen and relationship with litter quality under different understory vegetation in Pinus massoniana plantations

This study investigated aerially seeded Pinus massoniana plantations to analyze soil carbon and nitrogen distribution characteristics and the relationship with litter quality under two understory vegetation types (Dicranopteris and Graminoid) by using matched-pair t test and redundancy analysis. The results showed that:(1) At soil depths of 0-10 and 10-20 cm, soil organic carbon, microbial biomass carbon, dissolved organic carbon, total nitrogen, available nitrogen, microbial biomass nitrogen, and dissolved organic nitrogen were significantly higher for graminoid than for Dicranopteris (P < 0.05). However, at depths of 10-20 cm and 20-40 cm, the regularities of two understory vegetation types soil carbon and nitrogen indicators were different, but not significantly (P > 0.05). (2) The C content and C/N ratio of the semi-decomposed and undecomposed litter layer were significantly higher for Dicranopteris than for graminoid (P < 0.05). The N content of semi-decomposed and undecomposed litter layer of Dicranopteris were significantly higher than for graminoid (P < 0.05). The C content and C/N ratio of the undecomposed litter layer were significantly higher than of the semi-decomposed litter layer, and the N content of the semi-decomposed litter layer was significantly higher than of the undecomposed litter layer (P < 0.05). (3) At 0-10 cm, the C/N ratio and C content of litter were significantly negatively correlated with soil carbon and nitrogen (P < 0.05), and the N content was not significantly correlated with soil carbon and nitrogen (P > 0.05). At 10-20 cm, the semi-decomposed litter C/N ratio of Dicranopteris was significantly correlated with soil carbon and nitrogen (P < 0.05). The litter C content of graminoid was significantly correlated with soil carbon and nitrogen (P < 0.01). The lower litter C/N ratio of understory vegetation was associated with a faster litter decomposition rate, which was helpful for accumulating soil nutrients. The litter C/N ratio of graminoid was lower than that of Dicranopteris, explaining why the soil carbon and nitrogen indicators were significantly higher for graminoid than for Dicranopteris.