Effects Of Tending Measures On Site Environment And Growth In A Mixed Forest Of Dalbergia Odorifera And Santalum Album

Dalbergia odorifera+Santalum album mixed forest is a typical planting model of precious tree species in southern China.Because of its high economic value and market demand,the"orchard"management mode was put forward.The young growth forest management mainly replaces extensive traditional management by manual weeding and intensive cultivation and a large amount of fertilizer.Yet because Dalbergia odorifera+Santalum album mixed forests as a newly promoted model the nutrient cycling characteristics under different management practices and nitrogen fixation mechanism of mutual benefit,herbs and shrubs after removal of host’s influence on the growth of Santalum album are not clear,causing part of the mixed forests grow bad,easy to dry,but also significantly reduces the effect of the special forest ecological benefits.In addition,the previous studies on the parasitic relationship of this mixed forest mostly focused on the native Santalum album hosts,and there were few studies on the effects of the large herbage and shrub hosts under the forest on the absorption of parasitic nutrients of Santalum album,while the production practice found that the grass shrub hosts may have a greater impact on the growth promotion of Santalum album.Based on this,we carried out a study on the effects of weeding and fertilization on the growth and site environmental changes of mixed Dalbergia odorifera+Santalum album forest.Experimental studies on control check（CK）,weeding（W）,fertilization（F）and weeding+fertilization（W+F）were conducted in a mixed Dalbergia odorifera+Santalum album.The results showed that weeding had a significant impact on the soil environment,and the host of grass shrub contributed more to the growth of sandalwood,which were shown as follows:（1）Different tending and management measures had significant effects on soil available N、P、K nutrient contents under the mixed forests of Dalbergia odorifera+Santalum album（P<0.05）,had no significant effect on the total effective N、P、K content,and the nutrient content gradually decreased with the deepening of soil layer thickness,and the effect of nursing management gradually weakened.In the 0-10 cm soil layer,the effects of each treatment were the most significant.Compared with the control,the contents of soil alkali-hydrolyzed nitrogen in autumn weeding,fertilization and weeding+fertilization were increased by 8.61%,16.43%and 11.78%,respectively,and the differences between spring,summer and winter treatments were relatively small.Soil available P content was significantly different among different treatments in spring and autumn（P<0.05）,in spring weeding and weeding+fertilization increased by 53.75%and 55.54%,respectively,and fertilization decreased by 7.49%;The available P content increased by 35.59%and 9.08%in autumn fertilization and weeding+fertilization,respectively,while the available P content decreased by 4.22%in weeding,and there was no significant difference between winter and summer.The difference of soil available K content among all treatments was also significant in spring and autumn（P<0.05）,the content of available K decreased by 40.22%after weeding in spring,and increased by 20.47%and 6.72%after fertilization and weeding+fertilization,respectively;In autumn,weeding,fertilization and weeding+fertilization increased by 80.94%,133.55%and 105.72%,respectively,but there was no significant difference in winter and summer.Soil microbial biomass C and N contents had obvious seasonal variation characteristics,and there were significant differences among different tending and management measures（P<0.05）,and the difference was most obvious in autumn.Compared with the control group,the content of microbial biomass C in autumn was reduced by 26.31%,19.29%and 22.81%,respectively,by weeding,fertilization and weeding+fertilization.The N content of microbial biomass weeding,fertilization and weeding+fertilization decreased by 40.97%,50.73%and52.53%in autumn,respectively.The soil organic carbon content was decreased and the soil p H value was promoted obviously under different tending measures.（2）The results of different tending measures on understory vegetation diversity showed that there were 32 species,31 genera and 20 families,including 8 species,7 genera and 6families of woody plants,and 24 species,23 genera and 14 families of herbaceous plants（P<0.05）.The species richness index（R）,Simpson diversity index（D）,Shannon-Wiener diversity index（H）and Pielou evenness index(J_SW)of weeding and weeding+fertilization were significantly decreased（P<0.05）and little change in fertilization treatment.After continuous tending and management,the R value of the control and fertilization treatment changed steadily,while that of weeding and weeding+fertilization treatment increased year by year and finally surpassed the control.D value,H value and J_SW value of the control showed a decreasing trend year by year,while fertilizing treatment increased year by year,weeding and weeding+fertilization increased first and then decreased,and finally D value,H value and J_SW value were all the highest in fertilizing,while weeding was the lowest.Fertilization increased understory species diversity and showed an antagonistic effect to the decline of understory species diversity,while weeding aggravated the decline of understory species diversity.（3）The comprehensive analysis on the growth of Dalbergia odorifera+Santalum album mixed forest showed that the effects of management measures on the DBH of Santalum album were significantly different（P<0.05）,fertilization and weeding+fertilization increased by13.3%and 2.64%,respectively,while weeding inhibited the DBH growth and reduced the growth by 11.98%,and each treatment had no significant effect on the height growth of Santalum album.The effects of management measures on Dalbergia odorifera DBH is significant and tree height is not significant.Compared with the control,the DBH growth of Dalbergia odorifera was increased by 7.77%,9.36%and 13.83%by weeding,fertilization and weeding+fertilization,respectively.The growth of tree height increased by 3.54%,5.73%and7.32%,by weeding,fertilization and weeding+fertilization respectively.The effects of different treatments on the contents of N and K in leaves were significantly different（P<0.05）,there were no significant differences in P,Ca and Mg contents,compared with the control,the N content of Santalum album leaves was decreased by 1.97%after weeding,and the N content of Santalum album leaves was increased by 12.83%and 0.98%by fertilization and weeding+fertilization,respectively.Leaf K content decreased by 10.04%after weeding,and increased by 16.32%and 4.39%after fertilization and weeding+fertilization,respectively.There was no significant difference in the response of Dalbergia odorifera leaf nutrient to tending management of N,P,K,Ca and Mg.（4）The results of the study on the characteristics of litterfall in the mixed forest showed that the effects of different management measures on the annual litterfall amount were significantly different（P<0.05）,the litterfall amount in the treatment of fertilization increased by 26.88%,and the litterfall amount in the treatment of weeding+fertilization and weeding decreased by 6.57%and 17.99%,respectively.Among the components of litterfalls,the proportion of fallen leaves was the largest（62.23-73.55%）,followed by sundry matter（14.75-22.05%）,fruit and fallen branches was small.The monthly dynamic change pattern of litterfall in each treatment was bimodal curve,and the peak value was concentrated in summer and autumn,while the fluctuation was small in spring and winter.The annual nutrient return was N>K>P,in which the annual return of N increased by 56.26%and 14.25%of fertilization and weeding+fertilization,respectively,and weeding decreased by 9.90%compared with the control.The annual return amount of K was increased by 62.75%and 3.37%in the treatment of fertilization,weeding+fertilization,respectively,and decreased by 16.31%in the treatment of weeding.The annual return amount of P was increased by 28.34%in the treatment of fertilization,and decreased by 19.09%and 28.25%in the treatment of weeding+fertilization and weeding,respectively.The effects of different treatments on the quantity,composition and nutrient return of litterfalls were comprehensively analyzed.It was found that fertilization could significantly increase the nutrient return of litterfalls,while weeding could significantly reduce the nutrient return of litterfalls in the mixed Dalbergia odorifera+Santalum album mixed forest.The results showed that tending had a significant promoting effect on the improvement of undergrowth soil nutrients.Fertilization increased the diversity of undergrowth vegetation,while weeding significantly decreased the diversity of undergrowth vegetation.Compared with the control,after fertilization the DBH increment of Santalum album increased by 13.3%,weeding+fertilization increased by 2.64%,after weeding decreased by 11.98%;After fertilization,the Dalbergia odorifera DBH increment was increased by 9.36%,weeding+fertilization increased by 13.83%,weeding increased by 7.77%;Annual total litterfalls compared with the control,fertilization increased by 26.88%,weeding+fertilization decreased by 6.57%,and weeding decreased by 18.00%.In conclusion,fertilization can significantly promote soil nutrients,stand growth,nutrient cycle and understory vegetation diversity in the mixed stand of Dalbergia odorifera+Santalum album.However,Santalum album growth will be greatly damaged by weeding,which may eventually lead to the imbalance of interspecific relationship and the decline of mixed forest growth;fertilization after weeding could not make up for the adverse effect of Santalum album growth caused by the lack of Santalum album host.Therefore,it is very advantageous to apply fertilizer in the mixed stand of Dalbergia odorifera+Santalum album,but it is unfavorable to the stand growth to weeding comprehensively.