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

1. Calls for the application of ecological principles in agriculture have
gained momentum. Intercropping systems are designed by growing two, or
more, annual crop species in the same field, aiming for a better resource
use efficiency. However, assembly rules for their design are lacking.
Notably, it is unknown whether 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 can inform both
ecological theory and the understanding of the functioning of
intercropping systems. 2. We analyzed a dataset of 28 field cereal-legume
intercropping trials from various climatic and management conditions
across Western Europe. PRA was quantified in both mixing and
single-species situations. 3. PRA was positively impacted in specific
management conditions, leading to a greater increase in yield for a given
increase in plant size. Variations in PRA were more beneficial for legumes
grown in unfertilized mixtures, which explains their use as a key
component in actual intercropping systems. The response for cereals was
similar but less pronounced in magnitude, and was greater under resource
limiting conditions. Focusing on intercropping conditions, hierarchical
competition (indicated by biomass difference between intercropped species)
appears as a strong driver of the reproductive output of a given species.
4. Synthesis and applications. PRA behaves in crop species in the same way
as it does in wild species. However, contrary to theoretical expectations
about an overall invariance of PRA, we highlighted taxon-specific and
context-dependent effects of plant-plant interactions on PRA. This
systematic deviation to PRA expectations could be leveraged to cultivate
each species up to its reproductive optimum while accounting for the
performance of the other, whether farmer’s objective is to favor one
species or to reach an equilibrium in seed production. Sowing density and
cultivar choice could regulate the biomass of each component, with
specific targets derived from allometric relationships, aiming for an
optimal reproductive allocation in mixtures.21-Jul-2021