| Eucalyptus is one of the major timber species in southern China,Pure forest cultivation of Eucalyptus in large tracts of land can lead to some environmental problem,such as the decline of stand productivity and biodiversity reduction.The introduction of nitrogen-fixing species into Eucalyptus plantation can solve the ecological problems effectively.However,there was a lack of research on the combination of Eucalyptus/ nitrogen-fixing system and nitrogen management for the efficient utilization of nitrogen.Therefore,the study of the way to realize the efficient utilization of nitrogen fertilizer in Eucalyptus-nitrogen-fixing system is beneficial to improve the nutrient status of Eucalyptus plantation and provide scientific basis for the construction of reasonable management mode.With E.urophylla × E.grandis and D.odorifera as materials,potted trails were conducted in greenhouse to study the effects of N fertilization and rhizobia inoculation on growth status,photosynthetic characteristics,biomass accumulation,N nutrient uptake rates,soil microbial biomass and soil enzyme activity under E.urophylla × E.grandis-D.odorifera intercropping system.Aims to elucidate the effect of inoculating nitrogen-fixing bacteria to increase productivity,explore the optimum application of E.urophylla× E.grandis and D.odorifera intercropping system,and analysis the main factors affecting nitrogen absoration in E.urophylla × E.grandis and D.odorifera intercropping system.the main results obtained were as the following:(1)Nitrogen fertilization and inoculation had significant effects on height,ground diameter and biomass accumulation of E.urophylla × E.grandis,N3 level was the optimal treatment in both inoculation mode.Under N3 level,the plant height,ground diameter and biomass accumulation of E.urophylla × E.grandis reached the maximum under AJ treatment.Under JJ treatment,the plant height,ground diameter and biomass accumulation of E.urophylla × E.grandis reached the maximum under N3 level.Effects of JJ treatment on seedling height,ground diameter and biomass of E.urophylla × E.grandis was more significant than that of AJ treatment.Nitrogen application increases the growth of height and ground diameter of D.odorifera,but N3 inhibition the growth,so N2 level was the optimal treatment.With the inoculation mode was AJ,the plant height and ground diameter of D.odorifera seedling reached peak value under N condition was N2,the peak value under JJ mode also was with N2 level.Nitrogen application had a significant effect on the biomass accumulation of D.odorifera,the maximum of biomass showed at N2 level under two inoculation,plant height and biomass under the condition of AJ mode was higher than JJ,the ground diameter under JJ mode was higher than that of AJ,but there were not exist significant difference.(2)Nitrogen fertilization had signification effects on content of chlorophyll,MDA,soluble sugar,soluble protein the activities of NR,CAT of E.urophylla ×E.grandis,which showed a trend of N3>N2>N1>CK,The physiological characters of E.urophylla × E.grandis had different responses to the inoculated strains,among them,chlorophyll and NR activities in leaves of E.urophylla × E.grandis treated with JJ had the maximum,conversely AJ treatment had better effect on soluble sugar and soluble protein content.The soluble sugar,soluble protein of D.odorifera showed a trend of N2>N3>N1>CK,and the activity of NR reached the peak under the nitrogen level of N3.The differences of chlorophyll,soluble sugar and soluble protein were not significant,and activity of NR showed better performance under the condition of JJ.(3)Nitrogen application had a positive effect on the nitrogen absorption and utilization of in E.urophylla × E.grandis,nitrogen application and inoculating nitrogen-fixing bacteria was beneficial to increase the total nitrogen content in soil.Under two inoculation treatment,total nitrogen content,nitrate nitrogen content and ammonium nitrogen content of soil in N3 reached maximum,which was beneficial to the absorption of soil nitrogen by plants.Secondly,the interaction of nitrogen-fixing bacteria and nitrogen application promoted the nitrogen utilization rate E.urophylla × E.grandis.The nitrogen content of each organ and the whole plant of E.urophylla × E.grandis increased with the strength of the supply of nitrogen,which was significantly higher than that of the control group.At the same time,the nitrogen absorption amount of each organ and the whole plant of E.urophylla × E.grandis reached the maximum under the nitrogen condition of N3.Under the influence of nitrogen application,the nitrogen content and nitrogen absorption amount of D.odorifera showed different performance in the two inoculation modes.When inoculated AJ and JJ,the nitrogen content of each organ and the whole plant reached the maximum under the CK and N3 levels,while the nitrogen absorption amount of each organ and the whole plant reached the maximum at N2 and N3 levels.The combination of inoculation and nitrogen application had a positive effect on the nitrogen utilization rate of E.urophylla × E.grandis.Under AJ and JJ inoculation modes,the nitrogen utilization rate of eucalyptus urophylla urophylla reached 41.70% and 43.40% when the nitrogen level was N2.Moreover,the content of total nitrogen,nitrate nitrogen and ammonium nitrogen in soil under JJ treatment were higher than those in AJ treatment,which was the main reason why the nitrogen utilization of E.urophylla × E.grandis in AJ treatment was higher than that of JJ treatment.(4)Nitrogen application had a positive influence on the enzyme activity of rhizosphere soil in E.urophylla × E.grandis-D.odorifera intercropping system.The activity of leucine aminopeptidase(LAP),urease,polyphenol oxidase(PPO)and peroxidase(PER)enhanced with the nitrogen application rate in two rhizobia inoculation treatments.The activity of LAP,urease,PPO and PER reached the maximum at N3 level under AJ mode,the activity of LAP,urease,PPO and PER reached the maximum at N3 level under AJ mode.The effect of JJ is better than that of AJ under the same nitrogen condition.The microbial biomass of rhizosphere soil showed different change under the two inoculation treatments.The peak values of MBC and MBN under AJ treatment appeared in N2 and N1 level,while the peak values of MBC and MBN under JJ treatment appeared in N1 level.According to the results of ANOVA,the MBN content of soil was significant affected by the nitrogen application,inoculation mode and the interaction between them.(5)RDA analysis showed that soil total nitrogen content and root biomass were important environmental factors driving soil enzyme activity,and soil total nitrogen content and root biomass were positively correlated with content of soil MBC and MBN,activity of LAP,PPO,PER and urease.The interpretation amount of ammonium and nitrate nitrogen was second only to root biomass and soil total nitrogen content,and the relationship with soil MBC and MBN,LAP,PPO,PER,Urease activity was also close. |
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