Abstract
Published evidence indicates that nearly 60% of blueberry-producing countries experience yield instability. Yield is a complex trait determined by genetic and environmental factors. Here, using physiological and biochemical approaches, we tested the hypothesis that yield instability results from year-to-year environmental variation that limits carbon assimilation, storage and partitioning. The data indicate that fruit development depends primarily on the daily production of non-structural carbohydrates by leaves, and there is no accumulation of a starch buffer to allow continuous ripening under conditions limiting for photosynthesis. Photosynthesis was saturated at moderate light irradiance and this was mainly due to stomatal and biochemical limitations. In a dynamic light environment, photosynthesis was further limited by slow stomatal response to increasing light. Finally, labelling with 13CO2 at specific stages of fruit development revealed a relatively even distribution of newly assimilated carbon between stems, roots and fruits, suggesting that the fruit is not a strong sink. We conclude that a significant component of yield variability results from limitations in photosynthetic efficiency that are compounded by an inability to accumulate starch reserves in blueberry storage tissues in a typical northern European environment. This work informs techniques for improving agronomic management and indicates key traits required for yield stability in such environments.
Highlights
In fruit trees, photosynthesis and whole plant carbohydrate partitioning impact greatly on yield, and any factor that disrupts these processes may lead to fruit abortion and yield losses (Zhang et al, 2005; Teo et al, 2006; Gauci et al, 2009; Osorio et al, 2014)
The data indicate that fruit development depends primarily on the daily production of non-structural carbohydrates by leaves, and there is no accumulation of a starch buffer to allow continuous ripening under conditions limiting for photosynthesis
Yield-limiting factors may be related to adverse environmental conditions and insufficient pollen load, or to reduced carbohydrate reserves that result in competition between sink organs (Gauci et al, 2009)
Summary
Photosynthesis and whole plant carbohydrate partitioning impact greatly on yield, and any factor that disrupts these processes may lead to fruit abortion and yield losses (Zhang et al, 2005; Teo et al, 2006; Gauci et al, 2009; Osorio et al, 2014). Most species increase their photosynthetic capacity in environments with high versus limiting light availability, and mild versus extreme temperatures (Demmig-Adams et al, 2017) Environmental factors such as temperature have significant influence on carbon partitioning between different organs (Hancock et al, 2014; Pastenes et al, 2014; SalazarParra et al, 2015). In addition to environmental effects, photosynthetic capacity and carbohydrate partitioning are influenced by the competitive ability of a sink organ to import photoassimilates – a characteristic known as sink strength (Herbers and Sonnewald, 1998) Such regulation of photosynthesis by demand involves the activation of photosynthetic genes and is orchestrated by signals associated with the balance between carbohydrate production in leaves and its utilization in sink tissues (Foyer and Paul, 2001; Demmig-Adams et al, 2017). High sink strength enhances photosynthesis, whereas low sink strength leads to higher carbohydrate accumulation in leaves and subsequent feedback downregulation of photosynthesis (Demmig-Adams et al, 2017)
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