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Key message: Legume/nonlegume intercropping systems equipped with moderate nitrogen (N) application and PGPR inoculation could be exploited in eucalyptus growing areas and degraded land as an ecologically sustainable system to avoid excessive fertilization and enhance nitrogen use efficiency. Hazardous nitrogenous fertilizers in eucalyptus monocultures are challenging for the balance between eucalyptus wood production and ecological service functions. To assess whether plant growth-promoting rhizobacteria (PGPR) inoculation coupled with N application may improve plant growth by increasing biomass, photosynthesis, soil nutrient supply, and nutrient uptake capacity in the intercropping system. A pot experiment was performed to evaluate the synergistic effects of N application and N-fixing PGPR on growth, physiological parameters, N accumulation and nitrogen use efficiency (NUE) in intercropped Eucalyptus urophylla × Eucalyptus grandis (E. urophylla × E. grandis) and Dalbergia odorifera (D. odorifera). N fertilization positively influenced the plant height, dry matter yield, photosynthetic characteristics, N accumulation and nitrate reductase activity of E. urophylla × E. grandis under both inoculations. The growth and physiological traits of D. odorifera improved under the N2 (6 g N pot−1) application level. E. urophylla × E. grandis inoculated with Rhizobium japonicum IOC 113-2 showed higher values for plant height, biomass accumulation, N accumulation and photosynthesis with N fertilization, but the growth and physiological parameters of D. odorifera responded differentially to different inoculation treatments. The results demonstrated that an appropriate N supply in combination with N-fixing PGPR inoculation of legumes could increase nutrient absorption, NUE and yield advantages in intercropped E. urophylla × E. grandis and D. odorifera; thus, this method could be recommended as an alternative planting system under N-limited conditions in agroecosystems. [ABSTRACT FROM AUTHOR]

Background: The mixing of Eucalyptus with N2-fixing trees species (NFTs) is a frequently successful and sustainable cropping practice. In this study, we evaluated nitrogen (N) transfer and conducted a proteomic analysis of the seedlings of Eucalyptus urophylla × E. grandis (Eucalyptus) and an NFT, Dalbergia (D.) odorifera, from intercropping and monocropping systems to elucidate the physiological effects and molecular mechanisms of N transfer in mixed Eucalyptus and D. odorifera systems. Results: N transfer occurred from D. odorifera to Eucalyptus at a rate of 14.61% in the intercropping system, which increased N uptake and growth in Eucalyptus but inhibited growth in D. odorifera. There were 285 and 288 differentially expressed proteins by greater than 1.5-fold in Eucalyptus and D. odorifera roots with intercropping vs monoculture, respectively. Introduction of D. odorifera increased the stress resistance ability of Eucalyptus, while D. odorifera stress resistance was increased by increasing levels of jasmonic acid (JA). Additionally, the differentially expressed proteins of N metabolism, such as glutamine synthetase nodule isozyme (GS), were upregulated to enhance N competition in Eucalyptus. Importantly, more proteins were involved in synthetic pathways than in metabolic pathways in Eucalyptus because of the benefit of N transfer, and the two groups of N compound transporters were found in Eucalyptus; however, more functional proteins were involved in metabolic degradation in D. odorifera; specifically, the molecular mechanism of the transfer of N from D. odorifera to Eucalyptus was explained by proteomics. Conclusions: Our study suggests that N transfer occurred from D. odorifera to Eucalyptus and was affected by the variations in the differentially expressed proteins. We anticipate that these results can be verified in field experiments for the sustainable development of Eucalyptus plantations. [ABSTRACT FROM AUTHOR]