Cultivar mixtures increase stability and productivity over time through asynchrony and complementarity

Crop cultivar mixtures commonly increase productivity in the short term and stabilize or enhance productivity in the long term. However, these effects can be highly variable, likely due to limited research that has experimentally addressed intraspecific diverse effects over time and simultaneously explored their underlying mechanisms. We explored the effects of cultivar mixtures on the temporal yield stability and crop productivity trends in a 7-year (2016–2022) field experiment with maize in Northwest China. Further, we investigated the mechanisms underlying the enhanced productivity and temporal stability, which may be attributed to complementarity effects and asynchrony derived from functional trait dissimilarity among the maize cultivars in the mixtures. Across all cultivar mixtures over the 7 years, grain yield and aboveground biomass increased by 5.6% and 3.6%, respectively, compared to the monocultures. To investigate changes in temporal yield stability over the 7 years, we calculated stability using 3-year rolling windows. Our results showed that temporal yield stability in cultivar mixtures increased during the later years (2019–2022), compared to the monocultures. Over the 7 years, grain yield and aboveground biomass outperformed monocultures by 35% and 38%, respectively, compared to the first year. Complementarity effects were strong and increased over time. The mean values of functional traits changed in response to mixtures, leading to plant height and ear height traits correlating positively with complementarity effects, which were correlated with temporal yield stability. Asynchrony, or variation in the responses of cultivars to environmental fluctuations, was negatively correlated with the temporal deviation in yield. These results, for the first time, indicated that large differences in mean trait values among cultivars, or those that express dynamic trait responses to diversity, can increase complementarity effects and asynchrony, producing more productive and stable crops. This increases our understanding of how intraspecific diversity might contribute to sustainable agroecosystems.