| Eucalyptus urophylla is one of the most common plantation species in tropical and subtropical areas of China.It has been widely planted because of its characteristics of rapid growth and high output.However,due to the short cycle operation for a long time,some ecological problems,such as the serious invasion of exotic plants,the reduction of soil water conservation capacity,the decline of woodland fertility,the decrease of biodiversity and the weakening of ecosystem service function,are becoming more and more serious in E.urophylla forest management.Therefore,it is particularly important for E.urophylla plantation management to explore sustainable and ecologically beneficial planting patterns,effectively balance and coordinate wood production and other ecological service functions improvement.In this study,the mixed first-generation E.urophylla and Acacia mangium plantation(MP1),the mixed second-generation E.urophylla and Dalbergia odorifera plantation(MP2)was taken as our object,and the pure first-generation E.urophylla plantation(PP1),the adjacent pure second-generation E.urophylla plantation(PP2)was taken as the control(CK)respectively.Using a combination of field observation and indoor experiments,the study focused on the variation of carbon(C)and nitrogen(N)contents and their components in soil and aggregates after the introduction of nitrogen-fixing trees for long-term mixed planting,as well as the effects of nitrogen-fixing trees on the transformation process of C and N aggregates in E.urophylla plantations.In order to promote the sustainable development of E.urophylla plantations with high carbon sequestration,this study provided an important scientific basis for further understanding the distribution of C and N content and their components in aggregates,and the relationship between soil nitrogen components and soil carbon sequestration.The main results are as follows:(1)Nitrogen fixation tree species significantly increased the carbon and nitrogen content of PP soil and aggregates,and the highest content occurs in the aggregates with grain size <0.25 mm.Soil organic carbon(SOC)in MP1 were extremely significantly increased by 31.53%(p<0.001),45.99%(p<0.001),34.25%(p<0.001),40.08%(p<0.01)and 49.04%(p<0.01)in soil and aggregate particle size with>2mm,1-2mm,0.25-1mm and <0.25 mm compared with that in PP1.There was a significant increase in total nitrogen(TN),the increases were 39.08%(p<0.01),42.66%(p<0.001),40.24%(p<0.001),52.03%(p<0.001)and 30.08%(p<0.001),respectively.SOC in MP2 wereextremely significantly increased by 32.66%(p<0.001),32.92%(p<0.001),45.06%(p<0.01),47.45%(p<0.001)and 40.73%(p<0.001)in soil and aggregates compared with that in PP2.TN in MP2 significantly increased compared with that in PP2.The growth of soil and aggregates in >2mm,1-2mm,0.25-1mm and <0.25 mm were 13.22%(p<0.05),21.69%(p<0.05),28.28%(p<0.01)and 23.55%(p<0.01),respectively.(2)Nitrogen fixation species after a long period of mixed planting significantly increased the C and N components in soil and aggregates including LC-? and LN-?,LC-? and LN-?,RC and RN.Basically,the content of C and N components increases with the decrease of aggregate particle size,shows the highest content in<0.25 mm microaggregate.The recalcitrant index of carbon(RCI)of mixed forests increased significantly compared with that of pure forests,but the recalcitrant index of nitrogen(RNI)showed a downward trend.The results showed that the introduction of nitrogen-fixing trees improved the utilization efficiency of soil and soil aggregates N,reduced the proportion of recalcitrant nitrogen in TN,but increased the proportion of recalcitrant carbon in SOC,and improved the stability of soil organic carbon in eucalyptus plantations.(3)There is a certain Pearson correlation in the C,N components of soil and aggregates between PP and MP,and most of the correlations have reached the significance level.It shows a strong correlation between C and N components,specifically as follows:LC-?and LN-?,LN-?significant positive related;LC-?and LN-?significant positive associated;RIN was significantly positively correlated with RN and negatively correlated with other N components;Soil RC is in positively connection with all nitrogen components,but in negatively connection with RNI.(4)Nitrogen-fixing tree species significantly improved the microbial biomass of eucalyptus plantation soil and aggregates,and the soil hydrolytic enzyme activities involved in the conversion of soil C and N(except for leucine aminopeptidase).The phenol oxidase activity of soil and soil aggregates was significantly increased,but the peroxidase activity did not change significantly.There was a significant positive correlation between Ln(BG),Ln(CB),Ln(BG+CB+BX)and Ln(NAG+LAP),indicating that the change of N conversion caused by the introduction of nitrogen-fixing tree species.It would be the main driving force for soil C conversion,and there was a significant synergistic effect between C and N conversion.(5)This study shows that inter-planting nitrogen-fixing tree species like Acacia mangium or Dalbergia odorifera,may be an effective management measure to improve the soil nutrient quality of Eucalyptus plantations.It is an effective management measure to improve the stability and storage of organic carbon,so as to face the requirement of sustainable development in Eucalyptus plantations. |
PDF Full Text Request