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氮沉降已经成为全球变化背景下的热点问题,并呈现逐渐加重趋势,了解森林生态系统对这种持续氮增长和快速氮循环的响应模式及反馈机制,对于维护森林生态系统健康具有重要的理论意义。本研究选择不同林龄杨树人工林作为试验样地,设置N0(0 g N·m-2·a-1)、N1(5 g N·m-2·a-1)、N2(10 g N·m-2·a-1)、N3(15 g N·m-2·a-1)、N4(30 g N·m-2·a-1)5个不同浓度,进行氮沉降野外模拟实验,探讨不同林龄杨树人工林细根生物量的垂直分布及对模拟氮沉降的响应。结果表明:(1)70%~80%细根生物量分配在0~20 cm土层,呈现表层富集特征;外源氮增加后,幼龄林(4年生)中,0~10 cm土层细根生物量所占比例有所增加,而中龄林(8年生)和成熟林(15年生)则不同程度的减少;(2)细根生物量主要分布在0~0.5和0.5~1.0 mm径级,其中0~0.5 mm径级细根约占总细根(<2.0 mm)生物量的50%,外源氮输入增加极小径级(0~0.5 mm)的根系生物量,特别是幼龄林;(3)30~40 cm土层中,成熟林0~0.5 mm细根生物量分配量远大于幼龄林和中龄林,表明随着林龄的增加,小直径细根有向下分配趋势;(4)林龄、土层、径级以及施氮浓度4个因素的综合效应能够解释细根生物量66.3%的变异,其中林龄、土层、径级3个因素各自对细根生物量的影响极显著(P<0.01),分别能解释细根生物量17.6%、16.1%、10.4%的变异,而增氮处理仅能解释细根生物量0.24%的变异,影响效应不显著(P>0.05)。
Nitrogen deposition has become a hot issue in the context of global change and presents a gradual increasing trend. Understanding the response mechanism and feedback mechanism of forest ecosystems to such persistent nitrogen growth and rapid nitrogen cycle has important theoretical significance for maintaining the health of forest ecosystems . In this study, poplar plantations with different ages were selected as experimental plots. N0 (0 g N · m-2 · a-1), N1 (5 g N · m-2 · a- N · m-2 · a-1), N3 (15 g · m-2 · a-1) and N4 (30 g · m-2 · a-1) Experiments were conducted to investigate the vertical distribution of fine root biomass and its response to simulated N deposition in different stands of poplar plantations. The results showed that: (1) The fine root biomass of 70-80% was distributed in 0-20 cm soil layer, showing the characteristics of surface enrichment. After the increase of exogenous nitrogen, 0-10 cm soil The proportion of fine root biomass increased while the middle-aged forest (8-year-old) and mature forest (15-year-old) decreased to some extent. (2) Fine root biomass mainly distributed in 0 ~ 0.5 and 0.5 ~ 1.0 mm diameter, of which 0 ~ 0.5 mm diameter fine roots accounted for about 50% of total fine root (<2.0 mm) biomass, and exogenous nitrogen input increased root biomass of extremely small diameter (0 ~ 0.5 mm), especially (3) In the 30-40 cm soil layer, the fine root biomass allocation of 0-0.5 mm in mature soil was much larger than that in young and middle-aged forests, indicating that with the increasing of age, small diameter fine roots (4) The combined effect of four factors including age, soil layer, diameter class and nitrogen application rate can explain 66.3% variation of fine root biomass. Among them, three factors, stand age, soil layer and diameter grade, (P <0.01), respectively, which could explain 17.6%, 16.1% and 10.4% of the variation of fine root biomass respectively, while the increase of nitrogen treatment could only explain the variation of fine root biomass by 0.24% The effect was not significant (P> 0.05).