【目的】研究施用不同量沼液对杨树人工林细根生物量的影响,为科学利用沼液、优化杨树人工林施肥技术,以及促进杨树人工林可持续经营提供理论依据。【方法】在4种沼液施用量(0、125、250和375 m³/hm²)的杨树人工林长期控制野外实验样地,采用连续土钻法钻取不同土壤深度(0~20,≥20~40和≥40~60 cm)土芯样品;从中分拣出杨树活细根,经清洗、分级、烘干、称量,比较不同处理下的各土层、各径级细根生物量。【结果】0~60 cm土层总细根生物量、各层和各径级细根生物量均随沼液施用量的增加呈下降趋势。与对照相比,施用沼液使总细根生物量减少了18.8%~28.6%,尤其是土壤表层(0~20 cm)细根生物量减少最多,为21.5%~34.8%;1~5级细根生物量分别减少了17.7%~25.9%、8.5%~14.5%、17.6%~27.9%、10.9%~27.3%和24.4%~31.3%。【结论】长期施用沼液对杨树人工林细根生长有显著的抑制作用,且对细根垂直分布和径级分配有明显影响,但其作用机制还需深入研究。

【Objective】The aim of this study was to explore the effects of different dosages of biogas slurry on the fine root biomass of a poplar plantation, to provide a theoretical basis for utilizing the biogas slurry scientifically, optimizing poplar fertilization technology and promoting the sustainable management of soil fertility in poplar plantations.【Method】Because ammonium nitrogen is the main nitrogen compound in biogas slurry, four application levels of biogas slurry were set according to its ammonium nitrogen content and the available nitrogen content in the soil of the sample plot. The ammonium nitrogen content in the biogas slurry was 0, 1, 2 and 3 times the content of soil available nitrogen with the corresponding biogas slurry amounts as 0, 125, 250 and 375 m³/hm², respectively. There were three replicates for each application level and 12 quadrats. In May, August and October of each year, biogas slurry was applied to the surface by uniform sprinkling irrigation using pumps. In October 2018, the continuous soil drill method was adopted to randomly select three sampling points in each quadrat to remove the litter layer. A root drill with an inner diameter of 5 cm was used to drill the soil core samples of three layers from top to bottom. The soil samples collected from the three sample points in the same quadrat were mixed evenly and placed in labeled plastic bags before it was brought back to the laboratory. After soaking, rinsing and sieving the soil cores, live fine roots of poplar trees were sorted and 1-5 roots were separated using forceps. The separated root samples were baked in an oven at 80 ℃ for 48 hours to a constant weight and then weighed with an electronic balance (± 0.000 1 g).【Result】①With the increase in biogas slurry application, the total fine root biomass in 0-60 cm showed a decreasing trend. Compared with the control, the total fine root biomass in 0-60 cm was decreased by 18.8%, 28.6% and 23.6% with low, medium and high amounts of biogas slurry treatments, respectively. The analysis of variance showed that the total fine root biomass in 0-60 cm was significantly decreased by the medium biogas slurry treatment (P<0.05). ②With an increase in the amount of biogas slurry, the fine root biomass in all soil layers showed a downward trend. Compared with the control, the fine root biomass in the 0-20 cm soil layer decreased by 21.5%, 34.8% and 28.3% with low, medium and high amounts of biogas slurry treatments, respectively; while the proportion of fine root biomass in the total soil layer decreased by 3.0%, 6.9% and 5.1% with low, medium and high amounts of biogas slurry treatments, respectively. The analysis of variance showed that the fine root biomass of the 0-20 cm soil layer was significantly decreased by low, medium and high amounts of biogas slurry treatments (P<0.05). ③With an increase in the amount of biogas slurry, the total fine root biomass of grade 1-5 showed a decreasing trend. Compared with the control, low, medium and high biogas slurry treatments reduced the fine root biomass of grades 1-5 by 17.7%-25.9%, 8.5%-14.5%, 17.6%-27.9%, 10.9%-27.3%, and 24.4%-31.3%, respectively. The analysis of variance showed that the biomass of fine roots of grade 1 was significantly decreased by the low biogas slurry treatment (P < 0.05). Meanwhile, the medium biogas slurry treatments significantly decreased the fine root biomass of grades 1-5 (P < 0.05) and the high amount of biogas slurry treatments significantly decreased the fine root biomass of grade 3 and grade 4 (P < 0.05). In addition, in the 0-60 cm soil layer, biogas slurry treatments increased the ratio of the fine root biomass of the lower roots (levels 1, 2 and 3) and decreased the fine root biomass of the higher roots (levels 4 and 5). With an increase in the amount of biogas slurry, the fine root biomass of each layer decreased, except for the 1^st and 2^nd level fine roots in the middle layer (≥20-40 cm) and the lower layer (≥40-60 cm). The analysis of variance (ANOVA) showed that low amounts of biogas slurry treatments significantly decreased the first-order root biomass in the 0-20 cm soil layer (P<0.05). Medium biogas slurry treatments significantly decreased the fine root biomass at all levels in the 0-20 cm soil layer (P<0.05), increased the fine root biomass at all levels in the 20-40 cm soil layer (P<0.05), and decreased the fine root biomass at all levels in the ≥40-60 cm soil layer (P<0.05). A high amount of biogas slurry treatments significantly decreased the fine root biomass of levels 1, 3 and 4 in the 0-20 cm soil layer (P<0.05), and increased the fine root biomass of levels 1 and 2 in the ≥20-40 cm soil layer (P<0.05).【Conclusion】The long-term application of biogas slurry can significantly inhibit the growth of fine roots in poplar plantations, and significantly affect the vertical distribution and diameter class distribution of fine roots, which is an adaptation strategy for plants used to mitigate against environmental changes. However, the mechanism by which the indirect effect of biogas slurry on fine roots affects other elements of the soil environment requires further study.