Carbon source–sink limitations differ between two species with contrasting growth strategies

Abstract

Understanding how carbon source and sink strengths limit plant growth is a critical knowledge gap that hinders efforts to maximize crop yield. We investigated how differences in growth rate arise from source–sink limitations, using a model system comparing a fast‐growing domesticated annual barley (Hordeum vulgare cv. NFC Tipple) with a slow‐growing wild perennial relative (Hordeum bulbosum). Source strength was manipulated by growing plants at sub‐ambient and elevated CO2 concentrations ([CO2]). Limitations on vegetative growth imposed by source and sink were diagnosed by measuring relative growth rate, developmental plasticity, photosynthesis and major carbon and nitrogen metabolite pools. Growth was sink limited in the annual but source limited in the perennial. RGR and carbon acquisition were higher in the annual, but photosynthesis responded weakly to elevated [CO2] indicating that source strength was near maximal at current [CO2]. In contrast, photosynthetic rate and sink development responded strongly to elevated [CO2] in the perennial, indicating significant source limitation. Sink limitation was avoided in the perennial by high sink plasticity: a marked increase in tillering and root:shoot ratio at elevated [CO2], and lower non‐structural carbohydrate accumulation. Alleviating sink limitation during vegetative development could be important for maximizing growth of elite cereals under future elevated [CO2].

Genotypic variation in source and sink traits affects the response of photosynthesis and growth to elevated atmospheric CO2

“…This result suggests that genotypes with the higher constitutive sink capacity also had greater sink plasticity. In fact, studies reported a close correlation between adaptation to CO 2 enrichment and higher sink plasticity (Atwell, Kriedemann, & Turnbull, ; Burnett et al, ; Dahal et al, ; Kikuchi et al, ). However, to our knowledge, the genotypic covariation between sink strength and plasticity was never pointed out, in particular for traits involved in different phenological phases.…”

“…However, an increase in photosynthesis under e‐CO 2 was not systematically associated with an increase in grain yield (Ainsworth, ; Hasegawa et al, ; Kobayashi et al, ; Leakey et al, ; Long, Ainsworth, Leakey, Nösberger, & Ort, ; Long et al, ; Wang et al, ). One of the main hypotheses to explain this observation is that not only C source capacity but also C sink capacity drives crop production, and that either source or sink capacity alone cannot explain e‐CO 2 impacts on yield (Burnett, Rogers, Rees, & Osborne, ; Körner, ; Ludewig & Sonnewald, ; Sonnewald & Fernie, ).…”

Crops, Nitrogen, Water: Are Legumes Friend, Foe, or Misunderstood Ally?

“…These points fit well the 20-year-old observation by Hardwick [98], that rates of photosynthesis tend to follow seed development in grain legumes, rather than the reverse. Coupled with evidence that enhanced N transport to seeds promotes growth, and that the carbon:N ratio of phloem sap of legumes is generally conserved, it is reasonable to propose that engineering an enhanced ability to store N in seeds could well enhance rates of carbon fixation by legumes, a variant of the well-known, and increasingly well-elucidated, sink limitation of photosynthesis (Box 2) [99][100][101]. Box …”

The Role of Sink Strength and Nitrogen Availability in the Down-Regulation of Photosynthetic Capacity in Field-Grown Nicotiana tabacum L. at Elevated CO2 Concentration

“…The effects of the sink-source relationship in photosynthesis for plants grown under elevated [CO 2 ] conditions has been previously studied, most of the time in enclosed environments such as greenhouses, growth chambers and open-top chambers and often with potted plants (e.g., von Caemmerer and Farquhar, 1984; Arp, 1991; McConnaughay et al, 1993; Farage et al, 1998; Ainsworth and Rogers, 2007; Burnett et al, 2016). The use of pots can restrict the growth of sinks organs, like roots (Arp, 1991), and thus be a poor surrogate for understanding impacts of elevated [CO 2 ] on field crops.…”