Intraspecific trait variation mediates intercropping productivity under different spatial arrangements

Functional traits have advanced our comprehension of crop-crop interactions and intercropping outcomes. Nonetheless, the role of intraspecific trait variation (ITV) in influencing intercropping productivity across various spatial arrangements has received little attention. This study examined three aspects of crop ITV (i.e., the plastic variation in trait means, trait range, and trait coordination) in a field experiment on maize (Zea mays)-pepper (Capsicum annuum) strip intercropping. We set up different spatial arrangements with maize to pepper row ratios of 2:2 (M2P2), 2:4 (M2P4), and 2:6 (M2P6). Results indicated that M2P4 was the only spatial arrangement to achieve overyielding (mean LER = 1.09, p < 0.05). Intercropped maize consistently exhibited competitive advantages, but pepper displayed significant variability in biomass under different spatial arrangements. Compared to monoculture, intercropping increased the mean values of plant height and leaf area in maize (by 5.83 % and 4.67 % on average, respectively, p < 0.05), but had minimal influence on trait range and trait coordination of maize. However, intercropping significantly increased the mean values of 6 out of the 11 traits (p < 0.05) with a significant decrease in root diameter (p < 0.01), magnified trait range (by 26.5 % - 58.8 %, p < 0.05), and diminished trait coordination (especially M2P2 and M2P6, p < 0.05). Structural equation model analyses showed that plastic variation in trait means benefited the biomass of maize, but an increased trait range and elevated trait coordination favored the biomass of pepper. All three aspects of ITV functioned as effective mediators of the effect of spatial arrangement on crop-crop competition and intercropping productivity. Our findings suggest that intraspecific trait variation has considerable implications for the design of species-diversified agroecosystems.