Introduction of Dalbergia odorifera enhances nitrogen absorption on Eucalyptus through stimulating microbially mediated soil nitrogen-cycling

  Background  There is substantial evidence that Eucalyptus for nitrogen (N) absorption and increasing the growth benefit from the introduction of N-fixing species, but the underlying mechanisms for microbially mediated soil N cycling remains unclear.

  Methods  We investigated the changes of soil pH, soil water content (SWC), soil organic carbon (SOC), total N (TN), inorganic N (NH₄⁺-N and NO₃⁻-N), microbial biomass and three N-degrading enzyme activities as well as the biomass and N productivity of Eucalyptus between a pure Eucalyptus urophylla × grandis plantation (PP) and a mixed Dalbergia odorifera and Eucalyptus plantation (MP) in Guangxi Zhuang Autonomous Region, China.

  Results  Compared with the PP site, soil pH, SWC, SOC and TN in both seasons were significantly higher at the MP site, which in turn enhanced microbial biomass and the activities of soil N-degrading enzymes. The stimulated microbial activity at the MP site likely accelerate soil N mineralization, providing more available N (NH₄⁺-N in both seasons and NO₃⁻-N in the wet-hot season) for Eucalyptus absorption. Overall, the N productivity of Eucalyptus at the MP site was increased by 19.7% and 21.9%, promoting the biomass increases of 15.1% and 19.2% in the dry-cold season and wet-hot season, respectively.

  Conclusion  Our results reveal the importance of microbially mediated soil N cycling in the N absorption on Eucalyptus. Introduction of D. odorifera enhances Eucalyptus biomass and N productivity, improve soil N availability and increased soil C and N concentration, which hence can be considered to be an effective sustainable management option of Eucalyptus plantations.