Among plant traits, plant secondary metabolites such as tannins mediate plant–herbivore interactions but also have after‐life effects on litter decomposition and nutrient cycling. We propose that niche construction mechanisms based on positive plant–soil feedback (PSF) could influence the evolution of tannin production.By modelling the flow of nitrogen (N) and carbon (C) through plants and soil in a spatially explicit context, we explored the relative contribution of herbivory and positive PSF as drivers of tannin evolution. We assumed soil N to be contained in labile and recalcitrant compartments, the latter made of tannin–protein complexes from which plants can absorb nutrients via associations with mycorrhizal fungi.In infertile environments and for plants with low biomass turnover rates, we show that when tannins modify soil properties locally, positive PSF alone can drive their evolution. We further predict the existence of positive coevolutionary feedback between associations with mycorrhizal fungi with a decaying ability and tannins, possibly triggered by the evolution of the latter as protection against herbivores. In line with our theoretical results, empirical evidence suggest that tannins are mostly present in plants with low tissue turnover, associated with mycorrhizal fungi able to decay organic matter and inhabiting infertile environments.Synthesis. Our model proposes that the evolution of tannin production can be triggered by positive plant–soil feedback, provided that tannins promote the local N retention and that mycorrhizal fungi associated with plants are able to absorb N from tannin–protein complexes. In our model, tannin production evolves only in infertile ecosystems, in agreement with field observations. Our findings highlight that the strength of niche construction depends on the ecological context, hence that global ecological properties constrain local eco‐evolutionary dynamics.