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

Crop cultivar mixtures commonly increase productivity in the short term and stabilize and increase productivity in the long term, but these effects can be highly variable. This may be due to a poor understanding of the underlying mechanisms for such diversity effects. We explored mechanisms for the effects of cultivar mixtures on the temporal stability and intensification of productivity in a seven-year (2016-2022) field experiment with maize in Northwest China. Across all cultivar mixtures over the seven years, grain yield and aboveground biomass increased by 5.6% and 3.6%, respectively, compared to the monocultures, stability increased during the later years (2019-2022). Grain yield intensified by 35% and aboveground biomass by 38%, compared to monocultures. 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 higher in four-and eight-cultivar mixtures than in two-cultivar mixtures, and negatively correlated with the deviation in temporal yield. These results indicated that cultivars with large differences in mean trait values or 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.

作物品种混播体系通常可在短期内提升生产力，长期则可稳定并提升生产力水平，但此类效应的变异性极强。这一现象可能源于学界对这类多样性效应背后的核心机制尚缺乏充分认知。本研究依托中国西北2016-2022年开展的为期7年的玉米田间定位试验，探究了品种混播对生产力时间稳定性与增产效应的作用机制。7年间所有品种混播处理的籽粒产量与地上生物量，较单作处理分别提升5.6%与3.6%；且在试验后期（2019-2022年），生产力稳定性显著提升。相较于单作，籽粒产量的增产强度达35%，地上生物量的增产强度达38%。互补效应（complementarity effects）显著且随时间逐步增强。植物功能性状（functional traits）的均值因混播体系发生改变，其中株高与穗位高性状与互补效应呈显著正相关，而互补效应又与产量的时间稳定性呈正相关。异步性（asynchrony，即不同品种对环境波动的响应差异）在4品种与8品种混播体系中显著高于2品种混播体系，且与产量的时间偏差呈显著负相关。上述结果表明，平均性状值差异较大，或对多样性呈现动态性状响应的品种，可增强互补效应与异步性，进而提升作物的生产力与稳定性。本研究深化了学界对种内多样性（intraspecific diversity）如何助力可持续农业生态系统建设的认知。