New Discussion on Boysen-Jensen's Photosynthetic Response Curves Under Plant Canopy and Proposal of Practical Equations for Monitoring and Management of Canopy Photosynthesis

The name of Peter Boysen-Jensen brightly shines in the history of plant biology, especially as one of pioneering researchers studying the actions of plant hormones during phototropic responses as reviewed elsewhere (Pennazio, 2002; Enders and Strader, 2015), although the significance of some key experiments are questioned today (Yamada et al., 2000). Apart from plant growth regulation by light and/or plant hormones, Boysen-Jensen has two wellacknowledged contributions to photosynthetic studies, namely, a series of study on the photosynthetic assimilation and the study on the plant canopy structure. As reviewed elsewhere (Hirose, 2005), Boysen-Jensen have pointed out that the increase in dry mass reflects the photosynthetic assimilation of carbon dioxide (Boysen-Jensen, 1918; Boysen-Jensen and Müller, 1929a; 1929b), and he also deeply studied the photosynthesis under plant canopy structure in which the leaves of self and non-self origins are layered and compete for light (Boysen-Jensen, 1929; 1932). The most important factors to be discussed when relating the structural feature of plant canopy and functioning photosynthesis might be the utility of light at different positions within the canopy structure, as photosynthetic rate must be a function of light availability on site. The concept on the competition for light within plant community proposed by Boysen-Jensen is now the basis for understanding the eco-physiological behaviors of plants such as temperature-responsive onset of vegetation growth under competitive inter-species canopy (Dunnett and Grime, 1999).