Mixed Decomposition Effects Of Leaf Litter Of Eucalyptus Urophylla×e.Grandis And Five Tree Species And Their Effects On Soil Nutrients

Eucalyptus is the main timber species in South China.It has been widely planted in South China due to its advantages of rapid growth,high economic value and wide application.However,Long-term continuous planting of eucalyptus has caused a series of environmental problems of soil fertility decline,forest productivity degradation,environmental pollution and biodiversity loss,it can be effectively avoided through the mixed transformation of eucalyptus pure forest or the construction of mixed forest,and the selection of tree species is the key to the construction and transformation of mixed forest.Since litters are the main source of soil nutrients in forest land,introducing other tree species to form mixed forest with eucalyptus can change the composition and quantity of litters,regulate litter decomposition,improve soil nutrient status of forest land,and enhance the self-fertilizing capacity of forest land.Therefore,it is necessary to study the decomposition rate,element release rules and the feedback of soil fertility during the mixed decomposition of litters from eucalyptus and other tree species.In this study,the leaf litters of 6 main planted tree species of Eucalyptus urophylla×E.grandis(Eug),Acacia crassicarpa(Ac),Castanopsis hystrix(Ch),Michelia macclurei(Mm),Magnolia sumatrana var.glauca(Ms)and Mytilaria laosensis(Ml)in Guangxi were taken as the research objects,through the decomposition experiment in the field for 180 days,the mixed decomposition treatment of the leaf litters composed of Eug and other 5 tree species was compared with the single decomposition treatment of the leaf litters of Eug.And it analyzed the decomposition rate,element release regularity of mixed leaf litters and the feedback situation of the soil chemical properties systematically,which it aims to further reveal the effects of leaf litter mixing on decomposition processes and soil nutrient availability,and to provide the reference for a better understanding regularity of nutrient cycling in mixed forest land and selection of tree species in construction and modification of mixed forests related to Eug.The main research results of this study are as follows:(1)After 180 days of decomposition,the dry matter remaining rate of the leaf litters of Eug was higher than that of the mixed leaf litters.Among the mixed leaf litters,the highest was Eug×Ch,and the lowest was Eug×Ms.The negative exponential attenuation model showed that the distribution of decomposition coefficient k of each leaf litter was opposite to the dry matter remaining rate.The time for 50%decomposition(t_0.5)of each leaf litters ranged from 0.288 to 0.430years,and the time for 95%decomposition(t_0.95)ranged from 1.190 to 1.787 years.The decomposition rate of mixed leaf litters was higher than that of Eug,and the mixed leaf litters of Eug and Ms were the most obvious.Moreover,the synergistic effect was observed in mixing decomposition of leaf litters of Eug and Ch,Ms,and other mixed leaf litters decomposition only have a simple additive effect.Correlation analysis showed that the decomposition coefficient(k)of leaf litters was significantly positively correlated with the initial total nitrogen(TN)content,and significantly negatively correlated with the initial C:N ratio.(2)After 180 days of decomposition,the organic carbon(OC)content of most mixed leaf litters was lower than that of Eug,and the OC content of Eug×Ms decreased the most(6.58%).The total nitrogen(TN)content of Eug×Ac was significantly increased by 29.93%compared with that of Eug.The total phosphorus(TP)content of Eug×Ac and Eug×Ms increased by 12.97%and 9.73%compared with that of Eug,respectively,however Eug×Mm decreased by 12.43%.The C:N of Eug×Ac and Eug×Ms were 24.67%and 18.00%lower than that of Eug,respectively.There was no significant difference in C:P and N:P between mixed leaf litters and Eug.(3)The remaining rates of OC and N in all leaf litters were the highest in Eug×Ch,and the lowest in Eug×Ms.The P remaining rate in Eug was higher than that in all mixed leaf litters,and the lowest in Eug×Ms.The synergistic effect of C release was 33.3%and 50.0%of the decomposition time of Eug×Ac and Eug×Ms,respectively.The antagonistic effect and synergistic effect of C release were 33.3%and 16.7%of the decomposition time of Eug×Ml.The synergistic effect of N release was 16.7%,66.7%and 33.3%of the decomposition time of Eug×Mm,Eug×Ms and Eug×Ml,respectively.The antagonistic effect and synergistic effect of N release were 16.7%and 33.3%of the decomposition time of Eug×Ac,respectively.The synergistic effect of P release was 16.7%and 50.0%of the decomposition time of Eug×Ch and Eug×Ms.The antagonistic effect of P release was 33.3%of the decomposition time of Eug×Ml.Correlation analysis showed that the N and P remaining rates of leaf litters were significantly negatively correlated with the initial TN content,positively correlated with the initial C:N ratio,and the N remaining rate was negatively correlated with the initial N:P ratio.(4)Soil p H,soil organic carbon(SOC)and soil total phosphorus(STP)were not significantly different between Eug and mixed leaf litters during the process of decomposition,while soil total nitrogen(STN)under all mixed leaf litters was higher than that of Eug,with the highest increase(2.65%)in Eug×Ml.Soil C:N,C:P and N:P were not significantly different between Eug and mixed leaf litter.The soil ammonium nitrogen(SAN)and nitrate nitrogen(SNN)under the mixed leaf litters were increased compared with that of Eug,while the soil available phosphorus(SAP)had no significant difference with that of Eug.The SAN of Eug×Mm(9.76%)and Eug×Ms(5.73%)was significantly higher than that of Eug.The SNN of Eug×Mm increased the most(46.81%).