Abstract
Background and AimsShading by an overhead canopy (i.e. canopy shading) entails simultaneous changes in both photosynthetically active radiation (PAR) and red to far-red ratio (R:FR). As plant responses to PAR (e.g. changes in leaf photosynthesis) are different from responses to R:FR (e.g. changes in plant architecture), and these responses occur at both organ and plant levels, understanding plant photosynthesis responses to canopy shading needs separate analysis of responses to reductions in PAR and R:FR at different levels.MethodsIn a glasshouse experiment we subjected plants of woody perennial rose (Rosa hybrida) to different light treatments, and so separately quantified the effects of reductions in PAR and R:FR on leaf photosynthetic traits and plant architectural traits. Using a functional–structural plant model, we separately quantified the effects of responses in these traits on plant photosynthesis, and evaluated the relative importance of changes of individual traits for plant photosynthesis under mild and heavy shading caused by virtual overhead canopies.Key ResultsModel simulations showed that the individual trait responses to canopy shading could have positive and negative effects on plant photosynthesis. Under mild canopy shading, trait responses to reduced R:FR on photosynthesis were generally negative and with a larger magnitude than effects of responses to reduced PAR. Conversely, under heavy canopy shading, the positive effects of trait responses to reduced PAR became dominant. The combined effects of low-R:FR responses and low-PAR responses on plant photosynthesis were not equal to the sum of the separate effects, indicating interactions between individual trait responses.ConclusionsOur simulation results indicate that under canopy shading, the relative importance of plant responses to PAR and R:FR for plant photosynthesis changes with shade levels. This suggests that the adaptive significance of plant plasticity responses to one shading factor depends on plant responses to the other.
Highlights
Phenotypic plasticity in plants is their ability to change their phenotype according to the environmental conditions in which they grow (Bradshaw, 1965; Schlichting, 1986; Sultan, 2000)
An example of analysing the complex consequences of plant plasticity for plant performance is analysing the effects of phenotypic plasticity to shading caused by leaves on plant photosynthesis, which is an important plant performance measure
The objective of this study was to quantify the extent to which plastic responses to different shading factors interact in determining plant photosynthesis under different levels of canopy shading
Summary
Phenotypic plasticity in plants is their ability to change their phenotype according to the environmental conditions in which they grow (Bradshaw, 1965; Schlichting, 1986; Sultan, 2000). Plants grow in dynamic vegetation stands with other growing plants where they shade one another creating a light environment that varies considerably in time and space. This canopy shading entails multiple factors including reductions in photosynthetically active radiation (PAR) and changes in spectral composition especially reductions in the red (655–665 nm) to far-red (725–735 nm) ratio (R:FR) in addition to other spectral changes (Smith, 1982). Reductions in PAR induce plastic responses such as decreasing leaf photosynthetic capacity and respiration rate, changing leaf anatomy, increasing leaf photosynthetic nitrogen, increasing specific leaf area and increasing the fraction of assimilates partitioned to the leaf (Gulmon and Chu, 1981; Lichtenthaler et al, 1981; Walters et al, 1993; Evans and Poorter, 2001; Baird et al, 2017). Reductions in by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited
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