固氮树种旱冬瓜对退化林地土壤修复和林下植被重建的生态驱动效应

Effects of nitrogen-fixing tree species Alnus nepalensis on the degraded soils and understory restoration in the upper reaches of the Jinsha River, China

固氮树种对退化土壤和森林的结构与功能修复和改良具有重要价值,但是,固氮树种的混交配置、林龄变化和人工与天然起源林分对土壤修复和林下植被重建方面的生态驱动效应与影响机制的认识尚不够深入。因此,在金沙江上游选择退耕地上不同混交配置模式、不同林龄旱冬瓜(Alnus nepalensis)人工林和旱冬瓜天然次生林,对比分析了土壤养分、林下植被生长、林下植被多样性和旱冬瓜材积等指标的差异,以期阐明固氮树种旱冬瓜对土壤养分状况及林下植被重建的生态驱动效应。结果表明:(1)不同旱冬瓜人工林配置模式中,旱冬瓜纯林的土壤养分综合指标显著高于旱冬瓜+云南松混交林和云南松纯林(P<0.05);(2)不同林龄旱冬瓜人工林中土壤有机质、总氮及土壤养分综合指标呈现8年生林均显著大于5年生林(P<0.05);(3)土壤有机质、总氮及土壤养分综合指标均为旱冬瓜天然林>旱冬瓜和云南松人工混交林>云南松天然林(P<0.05);(4)SEM模型分析发现,旱冬瓜材积与土壤养分综合指标呈极显著的正相关关系(R=0.473,P<0.001);(5)在不同旱冬瓜人工配置模式和不同优势种的天然林中,灌木生长状况均与旱冬瓜材积呈显著正相关(R=0.496,P=0.014;R=0.610,P=0.002),且灌木生长状况与土壤有机质、总氮及土壤养分综合指标显著正相关(P<0.05)。研究揭示了固氮树种旱冬瓜作为退化土壤修复和植被重建的生态演替驱动种,显著提升了退化土壤的养分(有机质、总氮及土壤养分综合指标)并促进了林下灌木的生长,对加速金沙江上游退化土壤功能修复和林下植被重建具有积极生态驱动效应。

Nitrogen-fixing tree species play important roles in restoration and improvement in the degraded soils and forests. However, understanding the mechanism of nitrogen-fixing tree species underlying the degraded soil and forest restoration and reconstruction has still poorly known. Alnus nepalensis, a typical and native nitrogen-fixing tree species in the southwest of China, is widely used in plantations for maintaining or restoring soil fertility. In this study, we conducted a paired experiment to explore the effects of A. nepalensis on severely degraded soil amelioration and understory development by comparative analysis of soil nutrients, the growth and species diversity of understory vegetation in the plantations with different patterns of tree species mixture, different age-structure, and the plantation and natural forest. The results showed that:(1) the soil nutrients were significantly improved after planting A. nepalensis. Integrated Fertility Index(IFI) was significantly higher in the plots of A. nepalensis plantations(AP) than that of the mixed plantations(MP) and Pinus yunnanensis plantations(PP)(P<0.05).(2) IFI, organic matter(OM), and total nitrogen(TN) were significantly higher in the 8-year A. nepalensis plantations than that of the 5-year(P<0.05).(3) IFI, OM, and TN all showed the similar sequence, i.e., A. nepalensis forest>mixed forest>P. yunnanensis forest(P<0.05). The structural equation model(SEM) showed that there was a significantly positive correlation between soil nutrients properties and total volume of A. nepalensis(ATV).(4) According to the SEM, the ATV was positively correlated with the soil fertility(R=0.473, P<0.001).(5) In the plantations with different patterns of tree species mixture and in the natural forests with different dominant trees, the shrub growth was increased with the increasing of ATV(R=0.496, P=0.014;R=0.610, P=0.002), and the growth index of shrub were significantly positively correlated with OM, TN, and IFI(P<0.05). Overall, A. nepalensis demonstrated positive driving effects on ecological restoration of the degraded soils and understory growth in the upper reaches of the Jinsha River, China.