Abstract
BackgroundThe 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.ResultsN 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.ConclusionsOur 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.
Highlights
The mixing of Eucalyptus with N2-fixing trees species (NFTs) is a frequently successful and sustainable cropping practice
15N atom % in both species were detected (Fig. 2a and b), we found that N transfer occurred from D. odorifera to E. urophylla × E. grandis at a rate of 14.61%, which was equal to 150.62 mg of N transfer from D. odorifera to E. urophylla × E. grandis (Fig. 2c and d)
Our results showed that interspecific rhizosphere effects significantly improved N uptake and promoted the development of E. urophylla × E. grandis, but the effect on D. odorifera in the intercropping systems was limited, possibly because the root exudates by Eucalyptus had an allelopathic effect on D. odorifera [37]
Summary
The mixing of Eucalyptus with N2-fixing trees species (NFTs) is a frequently successful and sustainable cropping practice. Eucalyptus is widely planted in the tropics and subtropics and is one of the most important fast-growing trees for pulp and paper as well as the biorefinery industries [2], in subtropical China and throughout the world. While Eucalyptus is considered to have a high commercial value, its drawbacks include high levels of nitrogen (N), phosphorus and water consumption with successive rotations, all of which decrease productivity [4]. This phenomenon occurs because N availability is often a factor limiting Eucalyptus growth [5], and additional N input may be required to ensure high and sustainable stand production. Ecological mechanisms that occur in natural ecosystems to sustain productivity should be utilized [10], and the slight drop in productivity could be worth the reduced fertilizer costs if the difficulties of implementing mixed plantations are overcome by forest managers [1, 9]
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