Abstract
More efficient resource use, especially nitrogen (N) in agricultural fields could considerably reduce the losses and spillover effects on the environment. Cereal-legume mixtures can lead to more efficient uptake of growth-limiting resources, and increase and stabilize yields, due to the variation in functional traits that facilitate partitioning of niche space. Here we identify crop mixtures with functional traits that facilitate optimal N resource use in two selected cereal-legume mixtures by using the multi-dimensional trait space concept. Combinations of pea-barley and faba bean-wheat crops were grown in the field as pure cultures and mixtures in Central Sweden, during two years with contrasting weather. The ecological niche space was defined via the n-dimensional hypervolumes represented by N pool, tiller/branch number, shoot biomass, and grain yield functional traits. Regressions and correlations allowed quantifying the relations between functional traits and plant N pools. Differences in trait space were not a result of crop mixing per se, as similar hypervolumes were found in the pure culture and mixture-grown crops. Instead, the trait space differences depended on the cultivar identities admixed. Furthermore, cereals increased their efficiency for N uptake and therefore benefitted more than the legumes in the mixtures, in terms of accumulated N and grain yields. Tiller and shoot biomass production in cereals was positively correlated to N pool accumulation during the season. Resource acquisition through increased N uptake in the mixture was associated with a reduced overlap in niche-space in the mixtures, and initial seed N pools significantly contributed to within-season N accumulation, shoot and tiller production.
Highlights
The results presented for each crop included each of the three cereal cultivars grown in pure culture and with one legume cultivar
There was an effect of cultivar identity on hypervolume size in all crop species (p ≤ 0.001 in both barley and wheat, faba bean; p = 0.008, and for pea; p = 0.025)
We use trait hypervolumes to measure the overlap of ecological niche spaces in plant phenotypes (Blonder, 2018; Diaz et al, 2016) in pea-barley and faba bean grown at different crop mixing levels, to contrast species and cultivars differing in their N use
Summary
The use of cereal-legume crop mixtures can be associated with many benefits; for example, increased yield (Li et al, 2001; Ramirez-Garcia et al, 2015) and yield stability of the cereal-grain legume mixtures (Lauk and Lauk, 2008; Raseduzzaman and Jensen, 2017), improved grain quality and more efficient use of nutrient and water resources compared with the corresponding pure cultures (Li et al, 2006).more efficient resource use is one key attribute that practitioners of mixed cropping intend to achieve, through the explo ration of different resource niches (Bedoussac et al, 2015; Brooker et al, 2015). The use of cereal-legume crop mixtures can be associated with many benefits; for example, increased yield (Li et al, 2001; Ramirez-Garcia et al, 2015) and yield stability of the cereal-grain legume mixtures (Lauk and Lauk, 2008; Raseduzzaman and Jensen, 2017), improved grain quality and more efficient use of nutrient and water resources compared with the corresponding pure cultures (Li et al, 2006). The increased efficiency in resource use is attributed to the enhanced field level heterogeneity and positive in teractions that could result from the mixing of different crop cultivars (intraspecific diversity) or two or more crop species (interspecific di versity) at the same time (Mansion-Vaquie et al, 2019). To mechanis tically link the plant community responses and crop mixing to the properties of the involved species and cultivars, their functional traits can be studied
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