杉木×观光木异龄复层混交对林木生长及土壤理化性质的影响

为探究杉木纯林引入观光木转化为异龄复层林后土壤理化性质和土壤养分含量的变化特征，以及驱动土壤肥力变化的主要影响因子，以观光木纯林、杉木纯林和杉木林下套种观光木形成的杉木×观光木异龄复层林为对象，测定了3种林型下林分生长、林地土壤理化性质和养分含量及其化学计量比等指标，分析杉木×观光木异龄复层林林分结构、林木生长和土壤肥力质量特点。结果表明:1）异龄复层林中观光木和杉木的树高、胸径分别为5.3 m、2.52 cm和18.56 m、20.19 cm，显著高于纯林；2）3种林型间土壤物理性质差异显著。异龄复层林相比较纯林，土壤密度降低4.84%～11.94%，土壤孔隙度分别增加10.29%～22.27%，持水量增加8.62%～34.54%，有效改善了土壤孔隙结构和持水状况。3）各层土壤有机质、全N、全P、全K及速效养分与观光木、杉木纯林均差异显著，土壤养分含量随着土层加深而递减。各养分含量分别比杉木、观光木纯林高出7.87%～41.31%、14.32%～53.57%，各层土壤有机质和养分含量由大到小呈现为:异龄复层林、杉木纯林、观光木纯林。4）异龄复层林中C∶N、C∶P平均值分别为16.62、61.46，均低于杉木和观光木纯林，促进了土壤中N、P的有效释放。因此，在异龄复层林中观光木获得更适宜其生长的良好的遮阴环境，2个树种间形成生态位互补，提高了空间和自然资源的利用率，促进了树木生长。异龄复层林能显著提高土壤有机碳和养分含量，且明显高于纯林，在杉木林中套种观光木能加快土壤微生物的转化和矿化作用。

Growth and Soil Physicochemical Properties in the Mixed Forest of Cunninghamia lanceolata and Tsoongioden odorum in Different Aged and Multi-Layer Forests

In order to explore the change characteristics of soil physical and chemical properties and soil nutrient contents and the main factors driving the changes of soil fertility after the introduction of Tsoongioden odorum into the pure forest of Cunninghamia lanceolata,in this study,three forest types were used as the research objects,i.e.,pure T.odorum and C.lanceolata forests,different-aged and multi-layered mixed forest of T.odorum&C.lanceolata.The stand growth index,soil physicochemical properties,nutrient contents and stoichiometric ratios of three forest types were measured.The stand structure,forest growth and soil fertility characteristics were analyzed.The results showed that 1)the values of the tree height and diameter at breast height(DBH)of C.lanceolata and T.odorum in the mixed forest were 5.3 m,2.52 cm and 18.56 m,20.19 m,respectively,which were significant higher than those in pure forest.2)There were significant differences in soil physical characteristics among soil layers of 3 forest types.Compared with the pure forests,the soil density of the mixed forest decreased by 4.84%-11.94%,the soil porosity increased by 10.29%-22.27%,the water holding capacity increased by 8.62%-34.54%,and the soil pore structure and water holding capacity were improved.3)There were significant differences in soil organic matter,total nitrogen,total phosphorus,total potassium and available nutrients among pure and mixed forests.The nutrient contents of the mixed forest were 7.8741.31%and 14.32%-53.57%higher than those of C.lanceolata and T.odorum pure forests,respectively.The contents of soil organic matter and nutrients were in the order of mixed forest,pure C.lanceolata forest,pure T.odorum forest.4)The average values of soil C∶N and C∶P ratios in mixed forest were 16.62 and 61.46,respectively,which were lower than those of pure forests,indicating that in the mixed forest,both soil N and P effectively released.It was concluded that in the mixed forest,the T.odorum could obtain a better shade environment suitable for its growth,and the niche complementarity between the two tree species was formed,which improved the utilization rate of space and natural resources,and promoted the growth of trees.The contents of soil organic carbon and nutrients in the mixed forest were significantly higher than those in pure forest.Intercropping T.odorum in C.lanceolata forest could accelerate the transformation and mineralization of soil microorganisms.