Mixed plantations with N-fixing tree species maintain ecosystem C:N:P stoichiometry: Implication for sustainable production

Plant mixtures can enhance soil quality and optimize ecosystem carbon (C), nitrogen (N), and phosphorus (P) (C: N:P) stoichiometry to support sustainable production; yet this hypothesis has not been thoroughly examined in mixed plantations containing N-fixing tree species (N-fixers). Introduced N-fixers are often used as alternatives to N fertilization in forest plantations but may potentially disrupt the ecosystem C:N:P stoichiometric balance. Here, we compared the effects of N fertilization (100 kg N ha-1 year-1) and the introduction of an N-fixer (Dalbergia odorifera) into Eucalyptus plantations on the C:N:P stoichiometry across soil, microorganisms, enzymes, and leaves and roots. The experiment was organized into a randomized complete block design (n = 5) and lasted five years. N fertilization generally caused an imbalance in ecosystem C:N:P stoichiometry except for the microbial biomass C:N ratio. Introduced the N-fixers decreased the soil C:N ratio and increased the C:P and N:P ratios, whereas the other pools of C:N:P stoichiometry remained unchanged. Two meta-analyses further verified these findings, reinforcing the idea that mixed plantations with N-fixers, as a substitute for N fertilization, can help maintain ecosystem C:N:P stoichiometry to support sustainable production. Comparing the effects of N fertilization and introduced N-fixers using structural equation modeling approach underscored the importance of plant-microbial interactions in maintaining the balance of ecosystem C:N:P stoichiometry. This, in turn, can provide government and policymakers with compelling evidence for a nature-based solution for sustainable plantation management.