Grassland phases as ecological buffers: Reducing invasive weeds even under drought-induced stress in cropping systems

Agricultural systems are increasingly vulnerable to biological invasions and climate extremes, particularly drought, which can disrupt competitive balances and favor invasive weed establishment. Ecological strategies such as integrating temporary grassland phases into crop rotations offer potential to enhance system resilience, yet their long-term effectiveness under drought stress remains poorly quantified. A 12-year field experiment in western France was used to evaluated five rotational systems differing in the duration (3 or 6 years) and nitrogen fertilization of grassland phases within annual crop rotations. Weed invasion patterns were assessed using hierarchical statistical models, and an integrative drought stress index was developed to capture both the intensity and duration of water deficits over time. The influence of grassland management on invasive weed richness, temporal dynamics, drought sensitivity, and weed carryover between phases was examined. Invasive weed richness increased linearly with the proportion of annual crops, while systems with prolonged, well-fertilized grasslands exhibited significantly reduced invasion pressure—even under drought. Grassland phases buffered the effects of climate stress and minimized weed persistence across years, particularly when nitrogen inputs were adequate. Conceptualizing the system as a dynamic source–sink model revealed that crops serve as invasion sources, while well-managed grasslands act as ecological sinks that suppress invaders over time. These findings highlight the value of spatial–temporal diversification as a nature-based solution to reduce weed invasion in a changing climate. Incorporating extended grassland phases into rotations can strengthen agroecosystem resistance to invasive species and reduce dependency on chemical control strategies, contributing to the design of more sustainable and climate-resilient agricultural landscapes.