【目的】 探讨不同密度和水分管理下毛白杨(Populus tomentosa)林分细根分布特征,为优化华北平原杨树人工林的培育技术提供参考。【方法】于2021年,采用根钻法分别测定不同密度(以株行距表示,高密度3 m×3 m,中密度3 m×6 m,低密度6 m×6 m)和不同水分管理(FI,滴灌充分灌溉;NI,雨养)下的5种(FI高、FI低、NI高、NI低和NI中)毛白杨林分6 m剖面内的细根(直径<2 mm)生长及形态指标和土壤含水率,分析不同密度和水分管理下毛白杨细根分布特征。【结果】①高密度林分不同距树干距离细根分布较为均匀,而中密度和低密度林分细根随距树干距离的增加而减少。各处理毛白杨林木细根生长随土层深度增加而减少,且细根生物量密度(RBD)峰值出现在(0,20] cm土层内,范围为108.15~450.74 g/m3。②造林密度降低使林木细根趋于浅层化分布;而FI使得林木细根分布深度降低,其中,RBD累计比例达到50%所对应的土层深度最浅的处理为FI低,仅26.49 cm。③NI条件下,NI高[0,600] cm剖面平均RBD最低(58.16 g/m3),但增加了(100,400] cm土层细根生长分布;NI中增加了林木细根分布深度,加速了林分深层土壤水分的利用和消耗。相较于NI处理,FI处理减少了林木在30 cm以下土层中的细根生长分布。④NI条件下,密度对各土层细根形态特征均无显著影响。高密度林分中,FI高处理在(30,600] cm土层通过高比根长(24.45~90.97 m/g)、低组织密度(0.24~0.39 g/cm3)和小细根平均直径(0.20~0.32 mm)的高效细根形态结构来促进林木生长。【结论】毛白杨细根生长在[0,600] cm垂直分布,在5种处理中呈现出随土层加深整体减少的趋势。降低造林密度会使林木细根聚集在浅层,且减少深土层细根生物量的占比。NI条件下,高密度林分通过增加(100,400] cm的RBD来提高细根表面积(RSA)和细根根长密度(RLD),进而缓解由于林分密度过高引起的地下资源及空间的竞争;受株树密度和林木单株生长的影响,中密度林分增加了林木细根分布深度,加速了林分深层土壤水分的利用和消耗。FI处理下,高密度林分通过改善[0,600] cm剖面内林分细根的可塑性特征而不是细根生长来提升林木水分利用效率,以促进林木生长。
【Objective】 This study investigated the distribution characteristics of fine roots in poplar (Populus tomentosa) plantations under different stand densities and water management regimes, aiming to optimize cultivation techniques for poplar plantations in the north China Plain.【Method】In 2021, we employed the soil core method to analyze fine root (< 2 mm in diameter) growth, morphological indices, and soil water content with the 6 m soil profile across five treatment combinations: FIhigh (high density + full drip irrigation), FIlow (low density + full drip irrigation), NIhigh (high density + rainfed), NIlow (low density + rainfed), and NImedium (medium density + rainfed). Stand densities were categorized as high (3 m×3 m), medium (3 m×6 m) and low (6 m×6 m). The study assessed how density and irrigation (FI. full drip irrigation; NI. rainfed) influence fine root biomass distribution, vertical stratification, and horizontal extension.【Result】①In high-density stands, fine roots were uniformly distributed at varying distances from the tree base, whereas in medium-and low-density stands, fine root biomass decreased with increasing distance from the tree. ②Across all treatments, fine root biomass declined with soil depth, with the peak distribution of P. tomentosa fine roots occurring in the [0,200] cm layer (108.15-450.74 g/m3).③Reduced planting density led to shallower fine root distribution. Under FI, fine roots were concentrated in upper soil layers, with the shallowest cumulative 50% fine root biomass density (RBD) observed in the low FI treatment (26.49 cm). ④Under NI conditions, NIhigh exhibited the lowest mean RBD (58.16 g/m3) in the [0,600] cm profile but increased fine root growth in the (100,400] cm layer. NImedium enhanced deep root distribution and accelerated soil water depletion in deeper layers. Compared to NI, FI reduced RBD below 30 cm. ⑤Under NI, density had no significant effect on fine root morphology. However, in high-density stands, FIhigh promoted stand growth in the (30,600] cm layer via efficient root traits: high specific root length (24.45-90.97 m/g), low tissue density (0.24-0.39 g/cm3), and small mean diameter (0.20-0.32 mm). 【Conclusion】 Fine roots of P. tomentosa exhibit a vertical distribution within [0,600] cm, decreasing with depth across all treatments. Reducing planting density shifts fine roots upward, decreasing deep-layer biomass. Under NI, high-density stands enhance root boundary density (RBD) in the (100,400] cm range, improving fine root surface area (RSA) and length density (RLD), mitigating underground competition. Medium-density stands under NI promote deep root growth, accelerating deep soil water use. Under FI, high-density stands optimize root plasticity rather than biomass expansion to improve water-use efficiency and growth. These findings support climate-resilient poplar plantation strategies that balance productivity and sustainability in semi-arid regions.
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