Interspecific interactions regulate plant reproductive allometry in cereal-legume intercropping systems

1. Calling for ecological principles in agriculture has gained momentum. Intercropping systems have long been designed with the objective of optimizing resource use efficiency by growing two, or more, annual crop species in the same field. However, optimization criteria for their design are lacking. Notably, it is still unknown whether and how species performances are maximized during both the vegetative and reproductive phases given the sensitivity of reproductive allocation rules to resource limitation. Interestingly, ecological theory provides expectations regarding putative invariance of plant reproductive allometry (PRA) under non-limiting conditions for plant growth. Here we examined whether and how PRA changes in response to plant-plant interactions in intercropping systems, which represents a major inquiry for both ecological theory and the understanding of the functioning of intercropping systems.
2. We built and analyzed a unique dataset of 28 field cereal-legume intercropping trials from various climatic and management conditions across Western Europe. PRA were quantified in both mixing and single-species situations.
3. Management conditions significantly influenced PRA of the different components of the cropping systems. Deviations to PRA expectations were greater for legumes when grown in mixture, which explains their success in mixtures. The response for cereals was similar in direction but less pronounced in magnitude, and was more significant under limiting resource conditions.
4. Synthesis and applications. PRA matters in crop species in the same way as it does in wild species, suggesting the existence of universal biophysical constraints that cannot be broken by artificial selection. However, contrary to theoretical expectations about an overall invariance of PRA, our meta-analysis highlighted taxon-specific and context-dependent effects of plant-plant interactions on PRA. A systematic exploration of deviation to PRA expectations appears as a relevant tool to assist the management of intercropping systems through the choice of species and genotypes to use and the type of agricultural practices to apply. In turn, such a dialog between agronomy and ecology is a unique opportunity to challenge the validity domain and robustness of major ecological laws