DOI: 10.5061/dryad.9ghx3ffhv
title: Interspecific interactions regulate plant reproductive allometry in cereal-legume intercropping systems

description: 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
description: We collected a set of experiments that compared different species
 and cultivars under intercropping and sole-cropping conditions under a
 variety of management practices in 9 locations in five European countries
 (France, Denmark, Italy, Germany, and the United Kingdom). The experiments
 covered 28 environments (location × year), of which 15 were managed as
 organic farming and 13 as conventional farming, with a total of 34
 intercropping situations (environment × species) and 62 sole-cropping
 situations.<br> Since the experiments were not completely factorial,
 i.e. not all factors (cultivars, N fertilization, sowing density) were
 combined, we analyzed a total of 159 and 219 experimental units under
 intercropping and sole-cropping situations, respectively. In the
 experiments, 53% and 47% of the intercropped species were winter and
 spring crops, respectively. The mean temperature over the crop cycle (from
 sowing to harvest) ranged from 6.8-11.3 °C for winter crops and 12.3-15.1
 °C for spring crops. Cumulative rainfall ranged from 278-713 mm for winter
 crops and 60-366 mm for spring crops. The set of
 experiments included annual cereal-grain legume intercrops and their
 corresponding sole crops, with i) barley (Hordeum vulgare L.), durum wheat
 (Triticum turgidum L.) and soft wheat (Triticum aestivum L.) as the
 cereals (only Poaceae), and ii) faba bean (Vicia faba L.) and pea (Pisum
 sativum L.) as the legumes (Fabaceae). The cross between crop species and
 cropping seasons resulted in five intercropping combinations: two spring
 intercrops (barley-faba bean and barley-pea) and three winter intercrops
 (durum wheat-faba bean, durum wheat-pea and soft wheat-pea). In all
 experiments, the two intercropped species were sown and harvested at the
 same time, with sowing dates ranging from March 11 to May 03 for spring
 crops and October 25 to December 15 for winter crops.
 To assess reproductive effort and allometry, all experiments
 measured at least three variables: grain yield (t.ha -1 ) at harvest,
 total aboveground biomass (t.ha -1 , including grains, flowers, pods and
 ears) at maturity, and actual plant density (plant.m -2 ). Plant density
 was used to convert per-ha variables into per-capita variables (i.e.
 g.plant-1).