Background Phosphorus (P), iron (Fe) and zinc (Zn) are essential elements for plant growth and development, but their availability in soil is often limited. Intercropping contributes to increased P, Fe and Zn uptake and thereby increases yield and improves grain nutritional quality and ultimately human health. A better understanding of how intercropping leads to increased plant P, Fe and Zn availability will help to improve P-fertilizer-use efficiency and agronomic Fe and Zn biofortification.Scope This review synthesizes the literature on how intercropping of legumes with cereals increases acquisition of P, Fe and Zn from soil and recapitulates what is known about root-to-shoot nutrient translocation, plant-internal nutrient remobilization and allocation to grains.Conclusions Direct interspecific facilitation in intercropping involves below-ground processes in which cereals increase Fe and Zn bioavailability while companion legumes benefit. This has been demonstrated and verified using isotopic nutrient tracing and molecular analysis. The same methodological approaches and field studies should be used to explore direct interspecific P facilitation. Both niche complementarity and interspecific facilitation contribute to increased P acquisition in intercropping. Niche complementarity may also contribute to increased Fe and Zn acquisition, an aspect poorly understood. Interspecific mobilization and uptake facilitation of sparingly soluble P, Fe and Zn from soil, however, are not the only determinants of the concentrations of P, Fe and Zn in grains. Grain yield and nutrient translocation from roots to shoots further influence the concentrations of these nutrients in grains.
Photosynthesis in non-foliar organs plays an important role in crop growth and productivity, and it has received considerable research attention in recent years. However, compared with the capability of photosynthetic CO fixation in leaves, the distinct attributes of photosynthesis in the non-foliar organs of wheat (a C species) are unclear. This review presents a comprehensive examination of the photosynthetic characteristics of non-foliar organs in wheat. Compared with leaves, non-foliar organs had a higher capacity to refix respired CO , higher tolerance to environmental stresses and slower terminal senescence after anthesis. Additionally, whether C photosynthetic metabolism exists in the non-foliar organs of wheat is discussed, as is the advantage of photosynthesis in non-foliar organs during times of abiotic stress. Introducing the photosynthesis-related genes of C plants into wheat, which are specifically expressed in non-foliar organs, can be a promising approach for improving wheat productivity.
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