Artifleck: The Study of Artifactual Responses to Light Flecks with Inappropriate Leaves

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.

The effect of rapidly changing light on the rate of photosynthesis in largetooth aspen (Populus grandidentata)

Net photosynthesis by largetooth aspen was measured at each of four levels of irradiance, 3.4, 8.2, 22.6 and 73.1 W m−2 (0.4–0.7 μ), and during interchange of equal periods of these same levels. The periods between interchange ranged from about 0.2 to 300 s. All measurements were made between 17 and 19 °C; ventilation rate across leaves was equivalent to 1.5 m s−1. Photosynthesis was lower during interchange of long periods; depending on the irradiance levels selected, shorter periods led to increases in photosynthesis of up to 50%. Sometimes a recovery in photosynthesis occurred with the longest periods. The greatest changes were observed when one irradiance sequence was well below saturation level and the other was at or above saturation. Measurements of light regimes in three forest types showed that, during moderate winds at least, fluctuations with periods of between 0.1 and 100 s are commonplace. However, the effects of fluctuating irradiance on net photosynthesis may be important for growth and regeneration only where canopy height and spacings result in bright light flecks on other wise dark forest floors.