Abstract
In the current context of climate change, tree–crop combinations in agroforestry systems are suggested to mitigate water and heat stresses, particularly in semi-arid environments of the Mediterranean area. In this framework, a 3-year trial was conducted at the French National Research Institute for Agriculture, Food and the Environment (INRAE) in Mauguio (Southern France) in order to investigate the response of twenty-five durum wheat genotypes under a yearly pruned (AF) and a never-pruned alley olive orchard (AF+), in comparison with an open field without trees (control, C). The grain yield of wheat was markedly reduced in both the agroforestry systems AF (average −43%) and AF+ (−83%), according to the shading level. Among the yield components, the plant density at harvest was enhanced in AF (+22%) and AF+ (+3%), although with a significant reduction in the number of grains per spike (−37% in AF and −62% in AF+), and the number of spikes per plant (−32% in AF and −52% in AF+). The thousand-grain weight (TGW) and harvest index (HI) were slightly higher under moderate shade (AF; +12% vs. C) and severe shading (AF+; +6%). Plant biomass and spike size were significantly reduced in both agroforestry systems, while the flag leaf–spike distance (last internode) increased in AF. It was concluded that the moderate shading conditions of AF may create a sustainable agricultural system, and the wide intraspecific variability suggested a large scope for screening suitable genotypes, helping to produce ideotypes to implement agroforestry-oriented breeding programs.
Highlights
In the Mediterranean region, durum wheat yields and quality are increasingly affected by several abiotic constraints, notably spring/summer heat stress and drought, which are expected to intensify in the near future according to the International Food Policy Research Institute (IFPRI) prevision [1].The available climate models have predicted a probabilistic negative impact of climate change on wheat phenology and yield [2,3,4]
With regard to the grain quality, this study found an increase in protein content when the level of shading was increased, in agreement with similar studies [10,15,16], which was probably due to better remobilization of N in plant tissues and the generally negative correlation with grain yield; the size-exclusion high-performance liquid chromatography (SE-HPLC) used to investigate the protein composition highlighted that the %UPP was higher under full sun conditions
Durum wheat cultivation within the narrow alleys of olive orchards is an extreme continuous shading system that is suitable for highlighting the drawbacks and advantages of silvoarable models, whose reintroduction in the Mediterranean area is considered strategic due to climate change and land use
Summary
Grown in rows or as scattered trees, the olive trees have been intercropped with cereals, legumes, vegetables, and fodder crops for centuries, providing multiple products, such as grains, fruits, and fuel, for the maintenance of local communities. These ancient low-density orchards account for 70% of the current Mediterranean olive groves and are mainly located in the hilly, marginal, and rural areas [6,7]. A gradual abandonment of these olive groves has been documented in the last few decades due to their low productivity [8], the introduction of cereals and legumes intercropping and the implementation of suitable agroforestry practices might improve their productivity and sustainability
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