黄河三角洲滨海滩涂不同密度柽柳林的根系形态及生长特征

为探讨黄河三角洲滨海滩涂不同密度柽柳根系形态及生长特征，以山东省滨州港附近滨海滩涂的低密度（1100株/hm²）、中密度（4100株/hm²）和高密度（7100株/hm²）柽柳林为研究对象，采用全挖法对不同密度柽柳根系进行挖掘，测定分析柽柳地上生物量、根系生物量、空间分布特征、拓扑结构和连接长度等指标。结果表明：（1）中、高密度下，柽柳对根系生长的投入量更大，以保证对地下资源的吸收利用，根冠比分别为0.59、0.53；而低密度柽柳根冠比为0.44。（2）低、中密度下柽柳根冠生长关系均表现为异速生长，高密度下为等速生长。（3）不同密度柽柳根系生长都以水平分布为主，表现出水平根型特征。中、高密度柽柳根幅及侧根长均小于低密度，低密度柽柳根系水平分布范围最大，可利于增强觅养和固定能力。（4）林分密度与拓扑指数显著相关，低密度柽柳根系拓扑结构趋向于叉状结构（拓扑指数TI=0.62）；中、高密度柽柳拓扑结构趋向于鱼尾形分支（TI=0.86；TI=0.81）。（5）不同密度柽柳根系外部连接长度显著大于内部连接长度，呈现滨海滩涂柽柳根系向外扩张的生长策略。滨海滩涂不同密度柽柳根冠异速生长关系、根系形态及生长特征既有差异性又有相似性，表现出不同的密度适应特征。不同密度柽柳根系均以地表分布、向外扩张为主。低密度柽柳主要通过增加分支，扩大根系生长空间；中、高密度柽柳减少分支，加强对内部资源的利用，以降低与邻株间的竞争。柽柳密度与土壤含水量、电导率、扎根深度、侧根长、拓扑指数显著相关。

Root morphology and growth characteristics of Tamarix chinensis with different densities on the beach of the Yellow River Delta

The aim of this study was to explore the root morphology and growth characteristics of Tamarix chinensis with different densities on the beach of the Yellow River Delta. Low-density (1100 trees/hm²), medium-density (4100 trees/hm²), and high-density (7100 trees/hm²) T. chinensis near Binzhou Port in Shandong Province were used as the research objects. The full excavation method was used to excavate the root systems of T. chinensis with different densities; then, indicators such as aboveground biomass, root biomass, spatial distribution characteristics, topological structure and connection length were measured and analysed. The results showed that (1) under the conditions of medium- and high-density forests, T. chinensis invested more in root growth to ensure the absorption and utilization of underground resources, with root to shoot ratios of 0.59 and 0.53, respectively. The root-to-shoot ratio of low-density T. chinensis was 0.44. (2) The relationship between the root and shoot growth of T. chinensis under the conditions of low-density and medium-density indicated allometric growth, and under the conditions of high-density, it grew uniformly. (3) The root growth of T. chinensis grown at different densities was mainly distributed horizontally, showing the characteristics of horizontal root type. The root width and lateral root length of medium- and high-density T. chinensis were smaller than those of low-density T. chinensis, and the roots of low-density T. chinensis had the largest horizontal distribution range, which is conducive to enhancing foraging and fixing ability. (4)The density of T. chinensis was significantly correlated with the topological index. The root topology of low-density T. chinensis tended to be dichotomous (topological index TI=0.62), whereas the topological structure of medium- and high-density T. chinensis tended to be herringbone-like(TI=0.86; TI=0.81). (5) The external connection length of T. chinensis roots with different densities was significantly larger than the internal connection length, resulting in the outward expansion of the T. chinensis root system. In conclusion, there were differences and similarities in the root and shoot allometric relationship, root morphology and growth characteristics of T. chinensis growing in different densities in coastal mudflats, showing different density adaptation characteristics. The root systems of T. chinensis with different densities were mainly distributed near the ground surface and expanded outward. Low-density T. chinensis expanded its root growth space mainly by increasing the number of branches; medium- and high-density T. chinensis had fewer branches and strengthen the use of internal resources to reduce competition with neighbouring plants. T. chinensis density was significantly correlated with soil moisture content, electrical conductivity, T. chinensis root depth, lateral root length and topological index.