Purpose: This study explores the accumulation of phenolic acids in soil within monoculture plantations of Eucalyptus, Acacia mangium, contrasting with mixed species plantations containing both species, across various seasons. The research aims to provide insights into how different plantation types and species compositions influence the presence and levels of phenolic acids in soil. Methods: Soil phenolic acid concentrations were determined using HPLC, analyzing seven phenolic acids, including p-hydroxybenzoic, ferulic, coumaric, and benzoic acids. The kinetic adsorption experiments evaluated phenolic acid adsorption rates and quantities across various soil types. An adsorption kinetic model compared these concentrations between monoculture and mixed forest soils. Results: Our findings showed that plantation types, soil positions and seasons significantly impact phenolic acid accumulation. Non-rhizosphere soil in monoculture Eucalyptus plantations exhibited the highest phenolic acid concentration an average (32 µg g-1) across all seasons compared to mixed species plantations. Conversely, the rhizosphere soil of monoculture Acacia mangium displayed the highest content, reaching 71 µg g-1 in March. Notably, four phenolic acids (p-hydroxybenzoic, ferulic, coumaric, and benzoic acids) varied significantly between monoculture and mixed forests. Additionally, adsorption kinetic studies revealed that monoculture Eucalyptus and Acacia mangium soils had higher adsorption capacity compared to mixed species soils. The application of Elovich model yielded the best fit for ferulic and coumaric acids (R2 > 0.45). Conclusion: Mixed species plantations of Eucalyptus and Acacia mangium significantly influence soil phenolic acid levels compared to monoculture forests and induce alterations in soil adsorption characteristics for phenolic acids, potentially impacting soil fertility and productivity.

As phenolic acids accumulated in monocropping plantations, their allelopathic effects caused the soil’s fertility to decline and productivity to decrease. The effects of stand age and generational turnover of phenolic acids in soil remain unclear. Therefore, we conducted an experiment to examine the changes in phenolic acid content and accumulation characteristics in soils from Eucalyptus plantations in terms of planting years and generations. Soils were collected from three Eucalyptus plantations: a 6-year-old first-generation plantation (6a1g), 9-year-old first-generation plantation (9a1g) and 6-year-old second-generation plantation (6a2g). Seven phenolic acids were identified from different soil samples by high-performance liquid chromatography. In addition, exogenous phenolic acids were added to the soil samples to study the kinetics as well as the adsorption and desorption characteristics of soils. The total of seven phenolic compounds in 6a1g (38.451 μg g–1) was higher than that of the 9a1g and 6a2g soils, and the total of 6a2g (27.257 μg g–1) was higher than that of the 9a1g (15.536 μg g–1). In the tested soil, the p-hydroxybenzoic acid accounted for 51.6% (for 6a1g), 51.1% (for 9a1g) and 33.5% (for 6a2g) of the total amount of the seven phenolic acids, the p-hydroxybenzoic may have had a higher allelopathic capacity in these Eucalyptus plantation soils. Soil bulk density showed a strong positive correlation with vanillic and ferulic acids, and SOM also had an extremely positive correlation with p-hydroxybenzoic and coumalic acids. The findings demonstrated that the adsorption and desorption rates and amounts of each phenolic acid in the soil of 6a1g were higher than those in the soil of 9a2g and 6a2g using both a kinetic adsorption experiment and isothermal adsorption and desorption experiments. But among the three soils, 9a1g soil had the lowest adsorption rate, which resulted in the lowest accumulation capacity. It is noticed that the Pseudo-second-order kinetic model can be used to describe the kinetic adsorption better than the Pseudo-first-order kinetic model and the Elovich model, and the Freundlich model could fit the desorption isotherms better than the adsorption isotherms. However, more study of this phenomenon is essential to better understanding its mechanisms and how they function in order to address issues with soil degradation in future intergenerational Eucalyptus plantings.

通过研究桉树纯林与桉树和降香黄檀混交林土壤对香豆酸、香草酸和水杨酸的吸附动力学、等温吸附与解吸特性,探讨3种酚酸在不同林分土壤中的累积特征,评价桉树纯林引入降香黄檀后对林分酚酸物质累积的影响.采集5年生巨尾桉广林9号纯林及其与降香黄檀混交林地0～30 cm土层的土壤,采用添加外源酚酸方法和高效液相色谱仪检测酚酸吸附与解吸量.结果表明,3种酚酸在纯林与混交林土壤中的吸附都属于物理吸附,均表现4 h内快速吸附、4～24 h慢速吸附,随后逐渐达到吸附平衡;桉树纯林对酚酸的吸附速率大于混交林,随时间延长,纯林与混交林对酚酸的吸附速率基本一致.桉树纯林对酚酸的吸附动力学过程与Langmuir方程更吻合,而桉树与降香黄檀混交林与Elvoich方程更吻合.桉树纯林和混交林对酚酸的吸附过程与酚酸初始浓度呈正相关关系;2种林分土壤对不同酚酸的吸附量总体呈现为香豆酸>水杨酸>香草酸,且桉树纯林吸附量高于混交林;Freundlich方程能够较好地反映桉树纯林与混交林对酚酸的等温吸附特性.在2种林分土壤中香豆酸有一定的解吸率,香草酸和水杨酸解吸率较小甚至未发生解吸行为.香豆酸在高浓度400μg·mL-1时,混交林土壤的解吸率显著高于纯林,而低浓度时纯林土壤的解吸率高.

Accumulation of phenolic acids in monocropping plantations led to declining soil fertility and reduced productivity due to allelopathic effects. The effects of mixed versus mono-specific plantations on the seasonal turnover of phenolic acids in soil remains unclear. This study explored in plantations of Eucalyptus grandis × Eucalyptus urophylla and Erythrophleum fordii Oliv. (mixed) versus E. grandis × E. urophylla only (pure) the effect of species mixture on the phenolic acid content in the soil. We analyzed both total phenolic acid content as well as six phenolic acids separately and our measurements were conducted over four seasons and in an entire year. We expected that the mixed plantation would exhibit lower accumulation of both total and individual phenolic acids in soil versus the pure plantation. Contrary to our hypothesis, the Seite 332 Kebo Liao, Handong Gao, Mei Yang, Chengrui Liao total content of phenolic acids in the mixed plantation was significantly (p < 0.001) higher than that in the pure Eucalyptus plantation in all seasons. We also observed a significant effect of stand type (mixed or pure), season, and interaction between stand type and season on total soil phenolic acid content (p < 0.001). This may cause an enhanced allelopathic effect of phenolic acids in the soil of the mixed stand. In terms of the individual phenolic acids, the mixed plantation resulted in significantly higher (p < 0.001) p-hydroxybenzoic acid and vanillic acid contents in all seasons, as compared with the pure Eucalyptus plantation. Species mixture appears to reduce the content of ferulic acid, coumaric acid, benzoic acid, and salicylic acid in most seasons. A significant effect (p < 0.001) of stand type, season, and their interaction on the content of all individual phenolic acids in the soil, with the exception of benzoic acid, was observed. This study thus strongly suggests that both total and individual phenolic acids should be studied to evaluate the possible allelopathic effects in forest ecosystems and verify that species mixture can also increase phenolic acid concentration.

Accumulation of phenolic acids in monocropping plantations led to declining soil fertility and reduced productivity due to allelopathic effects. The effects of mixed versus mono-specific plantations on the seasonal turnover of phenolic acids in soil remains unclear. This study explored in plantations of Eucalyptus grandis x Eucalyptus urophylla and Erythrophleum fordii Oliv. (mixed) versus E. grandis x E. urophylla only (pure) the effect of species mixture on the phenolic acid content in the soil. We analyzed both total phenolic acid content as well as six phenolic acids separately and our measurements were conducted over four seasons and in an entire year. We expected that the mixed plantation would exhibit lower accumulation of both total and individual phenolic acids in soil versus the pure plantation. Contrary to our hypothesis, the total content of phenolic acids in the mixed plantation was significantly (p < 0.001) higher than that in the pure Eucalyptus plantation in all seasons. We also observed a significant effect of stand type (mixed or pure), season, and interaction between stand type and season on total soil phenolic acid content (p < 0.001). This may cause an enhanced allelopathic effect of phenolic acids in the soil of the mixed stand. In terms of the individual phenolic acids, the mixed plantation resulted in significantly higher (p < 0.001) p-hydroxybenzoic acid and vanillic acid contents in all seasons, as compared with the pure Eucalyptus plantation. Species mixture appears to reduce the content of ferulic acid, coumaric acid, benzoic acid, and salicylic acid in most seasons. A significant effect (p < 0.001) of stand type, season, and their interaction on the content of all individual phenolic acids in the soil, with the exception of benzoic acid, was observed. This study thus strongly suggests that both total and individual phenolic acids should be studied to evaluate the possible allelopathic effects in forest ecosystems and verify that species mixture can also increase phenolic acid concentration.

The impacts of thinning and fertilization on soil nutrient and tree growth in near-mature plantation of Cryptonmeria fortunei were studied by setting up three treatments, including thinning plus fertilization, thinning without fertilization and no-tending measures, respectively. The nutrition N, P, K in soil and the height and DBH of plantation were investigated and analyzed. The results showed that at the 0 ~20 cm layer, the content of available K showed significant differences between the treatments of thinning with fertilization and no-tending measures, while the contents of available P and hydrolysable N didn't significantly change with different treatments. The content of soil nutrients changed irregularly and not significantly at 20~40 cm layer. The growth increments of height and DBH in the thinned and fertilized plantation were higher than those in the other treatments, particularly, the growth of DBH had very significant differences between the thinned and fertilized stand and no-tending measures stand. The significant correlation was observed between the content of hydrolysable N and the growth of DBH. In addition, the highly significant correlation exited between the content of available K at upper layer and the content of available P at both layers. The thinning and fertilization improves the nutrient environment and increases the growth level of near mature C. fortunei plantation simultaneously.

The study on soil physical and chemical properties in pure forest of Cryptonmeria fortunei in Liuwan Forest Farm of Guangxi was intended to provide scientific reference for the reasonable planting density of Cryptonmeria fortunei in Guangxi.The density of four standard plots were 1 450 plant/hm2,1 800 plant/hm2,2 075 plant/hm2 and 2 700 plant/hm2,respectively.The analysis on physical and chemical properties of soil which sampled from each sample plot shows that soil bulk density tended to decrease with increasing density,was closely related with the soil water retaining capacity and soil porosity in soil physical properties aspect.The nutrition contents were higher at 0~20 cm depth than at 20~40 cm depth.Nutrition of upper layer changed irregularly under different stand density.The contents of soil organic carbon,hydrolysable nitrogen and soil available potassium were in the high level under 2 075trees /hm2 stand density.However,in subsoil soil organic carbon was positively correlated with stand density,soil available potassium changed irregularly and hydrolysable nitrogen increased at first and then decreased.Based on the soil physical and chemical properties,2 075 plant/hm2 should be the reasonable density to g ncrease the forest yield of Cryptomeria fortunei plantation in this area.

[Objective]The effects of density and mixed planting on stand growth in Guangxi Liuwan Forest Farm were studied to provide references for Cryptonmeria fortune planting and rational utilization of forestry resources in Guangxi. [Method]Five plantations were chosen, four of them were pure Cryptonmeria fortune plantations with the densities of 1450,1800,2075 and 2700 trees/ha,respectively,the other one was the plantation mixed Cryptonmeria fortune and Cunningham (7∶3) with the density of 1430 trees/ha. Average height, diameter at breast height (DBH), canopy, individual volume and stand stock of the chosen three sampling plots in each plantation were investigated and analyzed. [Result]Average DBH, canopy, height/diameter and individual volume tended to decrease with the increasing density. The densities showed obvious effect on distribution of DBH, the larger the density, the earlier DBH class peak. The stand stock for the four pure Cryptonmeria fortune plantations followed the trend:1450 trees/ha>2075 trees/ha>1800 trees/ha>2700 trees/ha. All the stand factors of growth in the mixed plantation were superior to that in any pure plantation. Compared to the pure plantation with similar density (1450 trees/ha), the individual volume increased by 47.3% and the stand stock increased by 32.0% in mixed plantation. [Conclusion]Mixed plantation of Cryptonmeria fortune and Cunningham is recommended to boost forest productivity.