Abstract:

The problem of succession barriers is one of the important factors limiting the development of Eucalyptus plantations in southern China, and the resulting ecological and environmental problems have made Eucalyptus plantation management controversial. The inter-root soil is an area where plants interact most frequently with the environment. It is important to correctly assess the effects of multi-generational succession on the characteristics and evolutionary trends of the soil organic environment in this area to solve the problem of successive plantations of Eucalyptus. We used Fourier transform infrared spectroscopy (FTIR) to characterize the structure and content of organic fractions in the inter-root soil of Eucalyptus urophylla plantation in southern subtropical new plantation (T0), sprouting 1 (T1), 2 (T2) and 3 (T3) generations, and also conducted a semi-quantitative analysis of organic functional groups. The organic fraction structure and content of soil organic fractions were characterized by FTIR. The results showed that the organic fractions in the inter-root soil of Eucalyptus plantations were almost the same among generations, with esters, aromatic, and phenolic alcohols accounting for a larger proportion, and aldehydes, polysaccharides, and carbonate ions accounting for a smaller proportion. However, the content of organic fractions in inter-root soils of eucalyptus plantations of different generations was significantly different (P<0.05), and the peak area integrals at 2929, 3423 and 3620 cm^-1 of the IR absorption spectra of soils in high generation (T2 and T3) stands were significantly higher than those of T0 and T1 treatments (P<0.05), mainly due to the differences in the contents of phenols, alcohols, and aliphatic hydrocarbons. The principal component analysis results (PC1 and PC2) explained 77.59% of the total variance, indicating that the functional groups above can reflect the distribution characteristics of soil organic functional groups. 2929, 3423, 1631, 3620 and 469 cm^-1 were the main effective functional groups in the T3 treatment, and the distribution of functional groups was more concentrated compared with those in the T0, T1 and T3 treatments. In summary, multi-generational succession promoted the increase of phenols, alcohols, and aliphatic hydrocarbons in soil, while the main functional groups of organic fractions gradually evolved from saturated to unsaturated states (C=C, C=O) in high generation Eucalyptus plantations, and the structure of organic functional groups tended to be homogeneous. These findings may provide a preliminary theoretical basis for further elucidation of the influence of the inter-root soil organic component structure on the microbial community structure and the interaction with plant roots.

Key words: Fourier transform infrared spectroscopy, soil environment, organic functional group, eucalyptus continuous planting, rhizosphere

摘要：

连栽障碍是制约中国南方地区桉树Eucalyptus（桉属植物）人工林发展的重要因素之一,由此带来的生态环境问题也让桉树人工林经营备受争议。根际土壤是植物与环境交互最为频繁的区域,正确评估多代连栽对该区域土壤有机环境特征及演变趋势的影响,对于解决桉树人工林连栽问题具有重要意义。以南亚热带新造林（T0）、萌芽1（T1）、萌芽2（T2）、萌芽3（T3）代尾叶桉（Eucalyptus urophylla）人工林根际土壤为研究对象,采用傅里叶变换红外光谱（FTIR）表征各代次桉树人工林根际土壤有机组分结构及含量特征,同时对有机官能团进行半定量分析,探讨多代连栽对土壤有机环境演变趋势的影响。结果表明：不同代次桉树人工林根际土壤有机组分大致相同,酯、芳香族以及酚醇类物质占比较大,醛、多糖类物质及碳酸根离子占比较小。但不同代次桉树人工林根际土壤有机组分含量具有显著差异（P<0.05）,其中高代次（T2、T3）林分土壤的红外吸收谱图2929、3423、3620 cm^-1处,峰面积积分显著高于T0、T1处理（P<0.05）,这主要是由于酚、醇类以及脂肪烃类物质的含量差异而引起的。主成分分析结果2轴（PC1、PC2）共解释了77.59%的方差,表明上述官能团能反映土壤有机官能团分布特征。T3处理中,主效官能团为2929、3423、1631、3620、469 cm^-1,官能团分布相对T0、T1、T3处理更集中。综上,多代连栽促进了土壤中酚、醇类物质及脂肪烃类物质的增加,同时高代次桉树人工林土壤有机组分主效官能团逐渐由饱和态向不饱和态（C=C、C=O）演变,有机官能团结构趋于单一。该结果可为进一步阐明根际土壤有机组分结构演变对微生物群落结构的影响以及与植物根系交互作用提供前期理论基础。

关键词: 傅里叶变换红外光谱, 土壤环境, 有机官能团, 桉树连栽, 根际土壤