【目的】细根生长与森林生产力的关系十分密切,而酚酸在根际的累积可能影响杨树根系形态建成及生物量分配进而影响生产力。笔者通过模拟杨树人工林根际酚酸环境,探究杨树幼苗根系形态建成对酚酸的响应,深入揭示根-土界面性质改变对林木根系生长的影响,为探明人工林根际过程和林分生产力之间的关系提供参考。【方法】以改良Hoagland 营养液为基础,参照连作二代杨树人工林土壤酚酸含量配制溶液并进行杨树幼苗培养。采集杨树幼苗根系,按50%的比例选取细根 (根径D < 2 mm) 样本并按根序进行分级,制作1~5级根序细根石蜡横剖面切片。采用根系扫描仪结合分析软件获得各根序细根的长度、直径,利用光学显微镜观察各根序细根的剖面直径、维管束(中柱)直径等参数,并计算比根长、根组织密度、维根比等。采用Origin Pro 8.0进行数据的差异显著性检验并作图,分析细根形态特征和剖面结构参数的相关性。 【结果】酚酸处理显著减少了杨树幼苗根系生物量。1~5级根序细根的生物量在对照和酚酸处理间无显著差异,但其所占生物量比例显著增加。酚酸处理总体抑制了杨树幼苗细根的伸长生长,1~3级根序细根的长度显著低于对照。酚酸处理具有增大杨树根系直径的效应,但1~5级根序细根的表面积在酚酸处理下均较对照显著下降。酚酸处理显著影响了杨树幼苗各根序细根的比根长和根组织密度,使比根长显著下降而根组织密度显著增大。此外,酚酸显著影响了杨树幼苗根系的生长发育,酚酸处理下1~5级根序细根的维根比显著增大,根系内输导组织分化显著。【结论】酚酸对杨树细根生长发育具有一定抑制作用,酚酸处理下不同根序细根形态的变化体现了根系功能的改变,这将影响根系吸收进而对杨树地上部分的生长产生抑制。不同根序细根形态建成的差异性也在一定程度上反映出酚酸影响下杨树根系的生长策略。

【Objective】 Forest productivity is closely related to fine root growth, and in this study, we simulated field concentrations of phenolic acids to examine the morphological responses of poplar seedling roots to phenolic acids. The objective was to provide in-depth insights into the rhizosphere effects of tree roots. 【Method】 Using an improved Hoagland solution, we generated phenolic acid environments designed to reflect the contents of phenolic acids in the soils of a successive rotation poplar plantation. All roots of poplar seedlings were harvested and 50% of the fine roots (diameter < 2 mm) were sampled and grouped according to order. A WINRHIZO root system analyzer and associated software were used to determine the morphological traits, including root length and diameter, of each fine root order (orders 1-5). Permanent paraffin cross-sections of fine roots of each order were prepared to observe anatomical traits, such as cross-section diameter and vascular cylinder (stele) diameter. Finally, several important parameters related to fine root morphology, including specific root length (SRL), root tissue density (RTD), and the ratio of vascular cylinder to cross-section area were calculated. Origin Pro 8.0 software was employed for data analysis and MS Excel was used to analyze the relationship between root morphology and the cross-section structures of the different fine root orders. 【Result】 We found that poplar roots biomass (dry weight) was significantly reduced after phenolic acid treatment. Although the biomass of fine root orders 1 to 5 showed no significant difference between the control check (CK) and phenolic acid treatments, the ratio of fine roots to total roots was significantly higher in seedlings receiving phenolic acid treatment than that of CK seedlings. Phenolic acids inhibited the elongation growth of fine roots, with the lengths of fine root orders 1 to 3 being significantly reduced under phenolic acid treatment. Furthermore, seedlings treated with phenolic acids showed an increase in fine root diameter, whereas the surface areas of fine root orders 1 to 5 were smaller under phenolic acid treatment than that of CK seedlings. Phenolic acids also affected the SRL and RTD, with the former being reduced and the latter increased in response to treatment. The anatomical traits of poplar roots were significantly altered under phenolic acid treatment, and the ratios of vascular cylinder to cross-section diameter of the roots of each order were increased, thereby indicating significant changes in the transport tissues of fine roots.【Conclusion】 Phenolic acids were found to have significant inhibitory effects on the fine root growth and development of poplar cuttings. The changes in fine root morphology revealed the variability in roots function under phenolic acid treatment, which would affect the absorptive function of fine roots and further inhibit the above-ground biomass growth of poplar. Furthermore, we characterized the strategies of tree root development and growth investment in response to phenolic acids with respect to differences in fine root morphology among different root orders.