Soil legacy effects of forage mixture and environmental stress enhance drought resistance in subsequent plants

Soil legacy effects arising from the individual or collective effects of environmental stress and plant diversity on subsequent plant growth because of modification of soil properties remain poorly understood. To address this, a two-phase experiment comprising regulation and feedback phases was performed. The aim is to examine how soil legacies generated by single or combined drought and salt stresses, alongside monoculture versus mixed planting of forage species, affect the growth and drought tolerance of subsequent maize (Zea mays L.). In the regulation phase, the four common forage species were cultivated under four distinct monoculture regimes and one mixed-species treatment. These plants were subjected to three stress conditions: drought, salt, and combination of drought and salt, with the objective of screening species-specific responses to these stresses. During the subsequent feedback phase, maize was grown in soils conditioned during the previous phase, under both well-watered and drought-stressed conditions. Key growth parameters were measured to assess the legacy effects. The results revealed that when drought stress was applied during the regulation phase, the mixed-species treatment yielded significantly higher aboveground and root biomasses than the monocultures, demonstrating a clear over-yielding effect. The aboveground biomass in mixtures reached 5.79 t∙hm⁻², close to the 5.81 t∙hm⁻² observed in non-stressed monocultures, underscoring the compensatory role of species complementarity in maintaining biomass production under stress. In the feedback phase under non-stress conditions, a significant interaction was observed between the prior plant diversity and the stress type applied during the regulation phase, which subsequently influenced maize biomass. Under drought conditions in the feedback phase, the soil legacy derived from mixed-species planting significantly enhanced the maize aboveground biomass, root biomass, and root-to-shoot ratio, improving the overall drought adaptive capacity of the crop. In summary, mixed planting fosters increased plant diversity, which results in a more resilient soil environment. The legacy effect of this environment can effectively buffer subsequent crops, such as maize, against the detrimental effects of abiotic stresses, such as drought. These findings offer valuable theoretical and practical insights for enhancing crop resilience in semiarid regions by optimizing planting strategies that leverage positive soil legacy effects.