黄河三角洲滨海滩涂不同密度柽柳林的土壤盐碱与养分特征

为探讨黄河三角洲滨海滩涂不同密度柽柳林的土壤盐碱和养分特征，明确不同密度柽柳林的“盐谷”及“肥岛”效应，以黄河三角洲山东省滨州市北海新区滨海滩涂的低密度（1100 株/hm2）、中密度（4100 株/hm2）和高密度（7100 株/hm2）柽柳林为研究对象，测定分析不同密度柽柳林及柽柳植株周边不同位置的土壤pH、电导率、速效氮、速效磷、速效钾、有机碳等指标。结果表明：（1）土壤电导率随林分密度增大表现为逐渐减小，在中、高密度柽柳林，土壤电导率分别比低密度降低28.39%、55.74%；随距离柽柳植株远近不同，中、高密度柽柳林土壤电导率表现为根部<冠幅中心<冠幅边缘<株间空地，即中、高密度柽柳林出现“盐谷”效应，而低密度林分未出现。（2）土壤速效氮、速效磷和有机碳含量随林分密度增大表现出先增大后减小，在中、高密度柽柳林，柽柳植株周边不同位置的速效氮、速效磷和有机碳含量存在显著差异（P<0.05），表现为根部>冠幅中心>冠幅边缘>株间空地，而低密度柽柳林差异不显著（P>0.05）；即中、高密度柽柳林出现“肥岛”效应，而低密度林分未出现。（3）中密度柽柳林在养分含量、养分富集率方面高于高密度，在盐分富集率方面低于高密度，具有更强的“肥岛”、“盐谷”效应。（4）不同密度柽柳林以及柽柳植株周边不同位置的土壤pH差异均不显著（P>0.05）。林分密度显著影响土壤盐分及养分含量，中密度柽柳林具有显著提高土壤肥力的作用，高密度次之，而低密度较差。不同密度柽柳林的降盐作用表现为中、高密度较好，低密度较差。基于柽柳林改良土壤盐碱与养分的作用，建议黄河三角洲滨海滩涂柽柳合理的初植密度为4100 株/hm2。

Variations in soil salinity and nutrient contents of Tamarix chinensis with different densities on the beach of the Yellow River Delta

This study aimed to explore the soil salinity and nutrient characteristics of different densities of Tamarix chinensis on the beaches of the Yellow River Delta, and to clarify the "salt valley" and "fertile island" effects of T. chinensis with different densities. This paper took the low-density (1100 trees/hm²), medium-density (4100 trees/hm²) and high-density (7100 trees/hm²) T. chinensis near Binzhou Port in Shandong Province as the research object. Soil pH, electrical conductivity, available nitrogen, available phosphorus, available potassium and other indicators of T. chinensis of different densities and different locations around the plants were measured and analyzed. The results showed that:(1) the soil electrical conductivity gradually decreased with the increase of density. In medium and high density T. chinensis forests, the soil electrical conductivity was reduced by 28.39% and 55.74% respectively compared with low density; Varying with the distance from the T. chinensis, the soil electrical conductivity of medium and high density T. chinensis showed the root < canopy center < canopy brim < interspaces. That is, the "salt valley" effect appeared in the medium and high density T. chinensis, but the low-density T. chinensis effect did not appear. (2) The contents of soil available nitrogen, available phosphorus and soil organic carbon first increased and then decreased with the increase of forest density. In medium and high density T. chinensis, there were significant differences in the contents of available nitrogen, available phosphorus and soil organic carbon at different positions of the T. chinensis (P<0.05), which was expressed as root < canopy center < canopy brim < interspaces, while there was no significant difference in low-density T. chinensis (P>0.05). The medium and high density T. chinensis had a "fertile island" effect, but the low-density T. chinensis did not appear. (3) Medium-density T. chinensis was higher than high-density in terms of nutrient content and nutrient enrichment rate, and lower than high-density in terms of salt enrichment rate. It had stronger "fertile island" and "salt valley" effects. (4) There was no significant difference in soil pH between different densities of T. chinensis and different positions around the plants (P>0.05). Forest density significantly affected soil salinity and nutrient content. Medium-density T. chinensis had a better effect on improving soil fertility, followed by high-density, and low-density was worse. The salt reduction effect of T. chinensis with different densities was better in medium and high densities, and worse in low densities. Based on the effect of T. chinensis on improving soil salinity and nutrients, it is suggested that the reasonable initial planting density of T. chinensis on the beaches of the Yellow River Delta was 4100 trees/hm².