| As one of the main fast growing timber species in Guangxi,Eucalyptus robusta robusta has many problems,such as single planting structure,short rotation period,improper management and so on.Therefore,it was urgent to study the structural adjustment of tree species.In this paper,five types of stands of Eucalyptus robusta robusta,Magnoliaceae glanca,Michelia hedyosperma,Magnoliaceae glanca X Eucalyptus robusta robusta and Michelia hedyosperma X Eucalyptus robusta robusta were studied.The growth and biomass accumulation of tree height,diameter at breast height,volume and volume were measured.The changes of soil physical and chemical properties and the effects of different mixed models on tree growth index,soil nutrients,soil enzyme activity and forest light resource utilization were investigated.According to forest survey Data and physical and chemical properties of soil were compared and analyzed.The results were as follows:(1)The three cultivation models of Eucalyptus robusta robusta,Magnoliaceae glanca X Eucalyptus robusta raobustaand Michelia hedyosperma X Eucalyptus robusta robusta,the height of the Eucalyptus robusta robusta,the diameter of the Eucalyptus robusta robusta,the individual volume and the accumulation of hectare were significant.The growth effect of the Magnoliaceae glanca X Eucalyptus robusta robustaand was the best,the average tree height of Eucalyptus robusta robusta was high,the average diameter of the breast and the score of the single plant were 14.2m,11.4cm,0.06386m3,and precious tree species.In the comparis was on between the mixed forest and the pure forest,the average tree of the mixed tree lotus of Eucalyptus robusta robustaand and Eucalyptus robusta robustaand was up to 3.4m,the average diameter was 3.3cm,the tree height was high,the diameter of the tree was 1.5,1.7 times of the pure forest of the tree lotus.Eucalyptus robusta robustaand mixed could promote the growth of the height and DBH of Magnoliaceae glanca,but the growth of Michelia hedyosperma and Eucalyptus robusta robustaand had little effect on the growth.In the mixed model,the biomass of Eucalyptus robusta robustaand mixed with Magnoliaceae glanca × Eucalyptus robusta reached the maximum value of 91.71kg/plant,which was significantly different from that of Michelia hedyosperma × Eucalyptus robusta robusta.The results showed that the mixture of Magnoliaceae glanca and Eucalyptus robusta robusta was beneficial to the biomass accumulation of Eucalyptus robusta robusta per plant.(2)There were significant differences in soil nutrients among different stands.The mixed soil N content of Michelia hedyosperma × Eucalyptus robusta robusta was beneficial to the accumulation of total N,and the content of available N reached the maximum value of 0.63 g/kg in the mixed soil.P content was lower than 1.0 g·kg in pure forest of Magnoliaceae glanca,and the total K content of soil was increased by pure forest of Michelia hedyosperma.By 0.68 g·kg.Tall Eucalyptus robusta,The growth of DBH and volume was significantly positively correlated with soil available potassium.The accumulation of biomass in Arbor layer was mainly affected by available N and P,and the correlation was significant.(3)The activities of soil invertase,soil urease and soil acid phosphatase in different stands were significantly different.Michelia hedyosperma X Eucalyptus robusta robusta soil invertase highest activity,do 98.172U/g·24h,Magnoliaceae glancasoil invertase lowest activity,do 29.093U/g·24h;Magnoliaceae glanca×Eucalyptus robusta robusta soil urease highest,do 4.702U/g·24h,Eucalyptus robusta robusta soil urease lowest,do 1.733U/g·24h;Michelia hedyosperma X Eucalyptus robusta robusta soil acid phosphatase highest,do 2.455U/g·24h,Magnoliaceae glanca soil acid phosphatase lowest,do 0.727U/g·24h;Magnoliaceae glanca X Eucalyptus robusta robusta soil catalase activity best of all,do 1.562U/g·24h,Michelia hedyosperma soil catalase activity worst,do 1.081U/g·24h.Accumulation and accumulation of Arbor layer Biomass in standsoil invertase andsoil catalase activity was significant correlation.Eucalyptus robusta robusta growth of tree height,diameter at breast height and volumelt was mainly affected by soil urease activity,there was a significant correlation.(4)Magnoliaceae glanca leaf area index was significantly different from the other four stands.Eucalyptus robusta robusta highest leaf area index was 1.61.Magnoliaceae glanca lowest leaf area index 0.98;Eucalyptus robusta robusta,Magnoliaceae glanca and Michelia hedyosperma were no significant difference in leaf inclination angle.Magnoliaceae glanca × Eucalyptus robusta robusta and Michelia hedyosperma × Eucalyptus robusta robusta were no significant difference in leaf inclination angle.Magnoliaceae glanca ×Eucalyptus robusta maximum blade inclination 35.09 °,Michelia hedyosperma minimum inclination of leaf was 21.93 °;Magnoliaceae glanca X Eucalyptus robusta robusta,Magnoliaceae glanca and Michelia hedyosperma X Eucalyptus robusta robusta were no significant difference in transmittance.Magnoliaceae glanca highest transmittance was 45.00%,Michelia hedyosperma lowest transmittance was 21.00%.The accumulation of tree height,DBH and volume had no significant correlation with leaf area index and leaf dip angle.However,there was a significant negative correlation between the light transmittance of the stand and the light transmittance of the stand.The accumulation of tree layer biomass has significant correlation with leaf area index,leaf dip angle and forest light transmittance.And there was a significant positive correlation with the light transmittance of the stand.Among the five afforestation models,mixed forest could promote the growth of the height of Eucalyptus robusta,while the high pure forest under the branch was significantly higher than the mixed forest.In the early stage of mixed breeding of Magnoliaceae glanca and Eucalyptus robusta,it was beneficial to the growth of the height and diameter of the tree,and the average crown width was significantly higher than that of the pure forest of Michelia hedyosperma in the mixed hybrid of Michelia hedyosperma and Eucalyptus robusta.The total N content of Eucalyptus robusta forest decreased with the depth of soil depth,while the total P content of the other four forest types was higher than that of mixed forest.The soil total K content of each stand increases with the increase of soil depth,and the available N content of soil of each stand was superior to that of pure forest of precious tree species.The soil available K content was higher in pure forest than in mixed forest.The available K content.of pure forest increased with the deepening of soil depth,while the available K content of mixed forest decreased with the increase of soil depth.The height of Eucalyptus robusta and the growth of DBH and volume were significantly positively correlated with soil available K,but not significantly or negatively correlated with total N,total K,total P,available N and available P.The biomass accumulation of Eucalyptus robusta was mainly affected by available N and available P,and the correlation was significant.The soil sucrase activity in mixed forest land was significantly higher than that in pure forest land,and the soil sucrase activity in surface soil of the same forest land was higher than that in pure forest land.The activity of the deep soil was higher than that of the deep soil.Soil urease activity in mixed forest land was significantly higher than that in pure forest land.The activity of acid phosphatase in mixed forest was significantly higher than that in pure forest,and the activity of acid phosphatase in surface soil of the same forest was higher than that in deep soil.The activity of catalase in woodland was higher than that in deep soil,but the activity of catalase in woodland was lower than that in deep soil in the same forestland,and the activity of catalase in surface soil was higher than that in deep soil in the same forestland.The accumulation of forest biomass was mainly related to the activities of urease and catalase.The height,diameter and volume of Eucalyptus robusta was mainly affected by soil urease activity,which was significantly correlated.The leaf area index of mixed forest was higher than that of pure forest,the dip angle of conifer was large,the leaf dip angle of broadleaf tree was small,the leaf area index was small,and the light transmittance of big dip angle was high.The accumulation of tree height,diameter at breast height and volume had no significant correlation with leaf area index and leaf inclination,but negative correlation with light transmittance of stand.The accumulation of tree layer biomass was significantly correlated with leaf area index,leaf dip angle and stand transmittance,and had a very significant positive correlation with stand light transmittance. |
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