Impacts of near-natural management in eucalyptus plantations on soil bacterial community assembly and function related to nitrogen cycling

Eucalyptus trees have been widely planted in China as commercial timber, which has caused severe soil erosion and water deficiency. Near-natural management by mixing eucalyptus with nitrogen-fixing tree species has been used in plantations to alleviate these problems. In the present study, we investigated the changes in soil microbial community and function in eucalyptus plantations mixed with nitrogen-fixing trees and with different rotation histories (first and second generation) using Illumina MiSeq. of 16S rRNA gene, coupled with Functional Annotation of Prokaryotic Taxa (FAPROTAX) and Quantitative Microbial Element Cycling (QMEC) analyses. Both management systems (mixed with nitrogen-fixing trees and with different rotating time) increased the soil bacterial alpha-diversity. The plantations with different management histories formed different bacterial communities and potential functional structures. Mixing with nitrogen-fixing trees increased the abundance of Actinobacteria involved in the nitrogen cycle and the abundance of K-strategy bacteria (Acidobacteria, Verrucomicrobia, Chloroflexi) in both first- and second-generation plantations. Functionally, the expression of nitrogen-fixing (nifH) and nitrification genes (amoA1 and hao) increased and that of denitrification genes (nirk2, nirk3, nirS1 and nosZ2) decreased in plantations mixed with nitrogen-fixing trees. The soil pH, soil water content and bacterial biomass were the key factors driving bacteria community and functional structures. The strategy of mixing eucalyptus with nitrogen-fixing trees can increase the efficiency of nitrogen cycling by accelerating the nitrogen-fixing and nitrifying process while inhibiting the denitrifying process. The results highlight the importance of mixing eucalyptus with nitrogen-fixing trees for soil microbes and provide useful information on the management of eucalyptus plantations in the future. Read the free Plain Language Summary for this article on the Journal blog.

Automated summary

Mixing nitrogen-fixing tree species with eucalyptus can improve the efficiency of nitrogen cycling in soil while mitigating soil erosion and water deficiency. Different management histories resulted in distinct bacterial communities and functional structures in the plantations. Mixing with nitrogen-fixing trees increased the abundance of nitrogen-fixing Actinobacteria and K-strategy bacteria, and inhibited denitrification.