2022 年 4 期目录

  目的  三倍体毛白杨作为华北平原重要的速生丰产树种之一，是我国木材战略储备的重要资源。滴灌水氮耦合技术已被广泛应用于人工林培育，掌握该栽培技术下毛白杨幼林细根生长、分布及形态特征，明确影响细根生长的重要环境因子，对精准水氮耦合策略的制定具有重要意义。  方法  以砂壤土立地条件下2年生毛白杨为研究对象，设置由?20 kPa（W20）、?33 kPa（W33）、?45 kPa（W45）3个灌溉水平和0（N0）、80 kg/（hm2·a）（N80）、150 kg/（hm2·a）（N150）、220 kg/（hm2·a）（N220）4个施氮水平组成的12个水氮耦合处理，并设置无灌溉施肥的对照处理，监测特定水氮耦合处理下（W20N220、W20N80、W20N0、W45N220、W45N0）幼林细根生长、分布及形态指标的变化规律，并分析对应土层土壤有机质、全氮、铵态氮、硝态氮及土壤含水率与细根生长的关系。  结果  （1）滴灌水氮耦合及土层深度对细根生长及形态指标有显著影响（P < 0.05）。其中，W20处理能显著促进0 ~ 20 cm土层细根生长（P < 0.05），细根趋于浅土层分布，而在W45N0处理下，0 ~ 30 cm土层比根长显著提高（P < 0.05）。（2）垂直剖面内，W20处理细根呈“由表层至深层降低”的分布规律，W45处理细根在不同土层内分布较均匀；水平方向上，细根分布呈“靠近树体，随径向距离增加而降低”的分布规律，但W20N220和W45N0处理细根生物量在同一径向位点无显著差异。（3）有机质、铵态氮和硝态氮均与细根生长呈显著的正相关关系（P < 0.05），且相关性强弱的顺序为有机质 > 硝态氮 > 铵态氮。  结论  W20滴灌施肥处理能显著促进表土层细根生长，不同施氮量对细根性状无明显影响；三倍体毛白杨优先改变细根生物量在不同土层的分配及部分形态特征，而非改变细根总生物量以适应水氮资源的异质性；滴灌水氮耦合措施实施的过程中，应采取少量多次的灌溉施肥方式对0 ~ 30 cm细根集中分布土层及时补充水氮资源，提高资源的吸收利用效率。 

Coupling effects of drip irrigation and nitrogen fertigation on fine root growth,distribution and morphological characters of 2-year-old Populus tomentosa plantations

  Objective  As one of the important fast-growing and high-yielding species in the North China Plain, the triploid Populus tomentosa is an important resource for the timber reservation strategy of China. Drip irrigation and nitrogen fertigation (DIF) technique has been widely used in plantation cultivation. Figuring out the responses of fine root growth, morphology traits and distribution pattern to DIF practices, and identifying the important environmental factors affecting fine root growth are of great significance for the formulation of precise water-nitrogen coupling strategies.   Method  The plant materials were 2-year-old P. tomentosa plantations on the sandy loam soil, and twelve DIF treatments were a factorial combination of three irrigation levels (?20 kPa (W20), ?33 kPa (W33), ?45 kPa (W45)) and four fertigation levels (0 (N0), 80 kg/(ha·year) (N80), 150 kg/(ha·year) (N150), 220 kg/(ha·year) (N220)), and the control treatment was with no irrigation and no fertigation. We monitored fine root traits and distribution patterns in 5 treatments, including W20N220, W20N80, W20N0, W45N220 and W45N0. Besides, we did the correlation analysis of soil properties (organic matter, total nitrogen, ammonium nitrogen, nitrate nitrogen, and soil water content) and fine root growth traits.   Result  (1) DIF treatments and soil depth had significant effects on fine root growth and morphology traits (P < 0.05). W20 associated treatments significantly stimulated fine root growth in 0?20 cm soil layers (P < 0.05), and the fine root accumulated in the shallow soil layers. The specific root length was significantly higher in 0?30 cm soil layers in W45N0 treatment (P < 0.05). (2) Fine root accumulated in the shallow soil layers and decreased with the increment of soil depth in W20 associated treatments, in contrast with the relatively uniform vertical distribution in W45 associated treatments. Fine root biomass accumulated near the trunk and decreased as the horizontal distance increased, and there was no significant difference of fine root biomass in W20N220 and W45N0 treatment in different horizontal locations. (3) Organic matter, ammonium nitrogen and nitrate nitrogen had significant positive correlations with fine root growth trait (P < 0.05), and the order of correlation was organic matter > nitrate nitrogen > ammonium nitrogen.   Conclusion  W20 associated treatments significantly stimulate fine root growth in the shallow soil layer, and the nitrogen fertigation has less effect on fine root traits; fine root growth and some morphological traits response to the resource heterogeneity in different soil layers for better resource acquisition rather than the mass plasticity in 2-year-old P. tomentosa plantations on the North China Plain. DIF practices should be applied with a little amount of water and nitrogen several times in 0?30 cm soil layers, which are concentrated with fine roots to improve water and nitrogen use efficiency.