Enhancement of nutrient absorption and interspecific nitrogen transfer in a Eucalyptus urophylla × eucalyptus grandis and Dalbergia odorifera mixed plantation

Abstract

There is substantial evidence that legume-derived nitrogen (N) is transferred to neighboring nonlegumes in herbaceous mixtures and intercropping systems. However, considering that woody species are key sources and major consumers N, information regarding whether N transfer from leguminous to nonleguminous woody species in mixed plantations was detected. To detect N transfer in a Eucalyptus urophylla × Eucalyptus (E.) grandis and Dalbergia odorifera mixed system, two pot experiments were set up, one with 15N dilution and the other with 15N leaf labeling of Dalbergia odorifera. Seedlings were fertilized with CO (15NH2)2 urea, and the effects on interspecific N transfer and biological N fixation (BNF) efficiency were observed. Results showed that: (1) The values of competition ratio of Eucalyptus urophylla × E. grandis to Dalbergia odorifera (CRED) greater than one indicate that Eucalyptus urophylla × E. grandis was a stronger competitor and had the absolute advantage over Dalbergia odorifera, N application significantly increased the competition ratio of Eucalyptus urophylla × E. grandis to Dalbergia odorifera. An increase in the dry matter yields of Eucalyptus urophylla × E. grandis was observed in the NB treatment (20.36–33.16%), but the dry matter yields of Dalbergia odorifera decreased by 10.02–19.57%. (2) N was transferred from Dalbergia odorifera to Eucalyptus urophylla × E. grandis at rates of 9.60% and 6.50% in the 3 and 6 g pot−1 urea treatments with isotope dilution markers, respectively. N transfer rates of 13.66% and 7.88% were observed in the NB and MB treatments with 15N leaf labeling. (3) Interspecific root interaction increased N use efficiency and increased N2 fixation by Dalbergia odorifera; N fixation increased by 8.51% and 4.34% at the N1 and N2 levels under the NB treatment. The biomass and N use efficiency of Eucalyptus urophylla × E. grandis and Dalbergia odorifera has grown together were effectively improved compared to those of monocultures. The mechanism for our results may depend on interspecific N transfer, i.e., N transfer from Dalbergia odorifera to Eucalyptus urophylla × E. grandis, the stimulation of Dalbergia odorifera BNF and its increased use of atmospheric N sources may improve the exploitation of mixed plantations.