Abstract
Methods in sunfleck research commonly employ the use of experimental leaves which were constructed in homogeneous light. These experimental organs may behave unnaturally when they are challenged with fluctuating light. Photosynthetic responses to heterogeneous light and leaf macronutrient relations were determined for Cycas micronesica, Glycine max, and Zea mays leaves that were grown in homogeneous shade, heterogeneous shade, or full sun. The speed of priming where one light fleck increased the photosynthesis during a subsequent light fleck was greatest for the leaves grown in heterogeneous shade. The rate of induction and the ultimate steady-state photosynthesis were greater for the leaves that were grown in heterogeneous shade versus the leaves grown in homogeneous shade. The leaf mass per area, macronutrient concentration, and macronutrient stoichiometry were also influenced by the shade treatments. The amplitude and direction in which the three developmental light treatments influenced the response variables were not universal among the three model species. The results indicate that the historical practice of using experimental leaves which were constructed under homogeneous light to study leaf responses to fluctuating light may produce artifacts that generate dubious interpretations.
Highlights
The conversion of light energy into biomass through plant photosynthesis has been aggressively studied for decades
Cycad leaves, developed in homogeneous shade conditions of 62% light exclusion, exhibited minimum and maximum net CO2 assimilation (Pn) in fluctuating light that was similar to the leaves that developed in heterogeneous shade of 62% light exclusion (Figure 1)
The shade leaves from the homogeneous light treatment required five sequential light flecks to reach the maximum Pn, but the leaves from the heterogeneous light treatment reached maximum Pn after only three light flecks
Summary
The conversion of light energy into biomass through plant photosynthesis has been aggressively studied for decades. A continually changing PPFD occurs due to factors such as ephemeral cloud cover, atmospheric conditions that define the extent of diffuse light, the movement of leaves, the size and stratification of canopy foliage gaps, and the changes in angle of the solar beam throughout a photoperiod [1,2,3]. This chronically changing PPFD places the photosynthetic machinery under conditions that do not conform to the experimental methods in studies which employ constant. The improvement of crop performance should include the study of steady-state photosynthetic capacity, and the photosynthetic traits that define leaf performance in fluctuating light [7,8]
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