Differential responses and mechanistic controls of soil phosphorus transformation in Eucalyptus plantations with N fertilization and introduced N2-fixing tree species

Introducing N-2-fixing tree species into Eucalyptus plantations could replace nitrogen (N) fertilization to maintain high levels of N consumption and productivity. However, N enrichment may exacerbate phosphorus (P) limitation as Eucalyptus robusta Smith is extensively planted in P-poor tropical and subtropical soils.We conducted a field experiment in a pure plantation of Eucalyptus urophylla x grandis to investigate the impacts of N fertilization and introduced an N-2-fixing tree of Dalbergia odorifera T. Chen on soil P transformation.Nitrogen fertilization significantly enhanced soil occluded P pool and reduced the other P pools due to acidification-induced pH-sensitive geochemical processes, lowering Eucalyptus leaf P concentration with higher N : P ratio. By contrast, introduced N-2-fixing tree species did not change soil pH, labile inorganic P pool, and Eucalyptus leaf N : P ratio, even enhanced organic P pools and reduced occluded P pool probably due to altering microbial community composition particularly stimulating arbuscular mycorrhiza fungal abundance.Our results revealed differential responses and mechanistic controls of soil P transformation in Eucalyptus plantations with N fertilization and introduced N-2-fixing tree species. The dissolution of occluded P pool along with organic P accumulation observed in the mixed plantations may represent a promising future to better manage soil P availability.

Automated summary

Introducing nitrogen-fixing tree species into Eucalyptus plantations can maintain high levels of nitrogen consumption and productivity, but may exacerbate phosphorus limitation. A field experiment was conducted to investigate the impacts of nitrogen fertilization and introducing a nitrogen-fixing tree species on soil phosphorus transformation in a pure Eucalyptus plantation. Nitrogen fertilization significantly increased the occluded phosphorus pool and reduced other phosphorus pools, while introducing the nitrogen-fixing tree species did not change soil pH or the nitrogen:phosphorus ratio in Eucalyptus leaves.