Pigment contents, leaf structure and light response of photosynthesis in sun and shade leaves

Shade plants have to cope with much less light than sun plants. In the sun, investment into high photosynthetic capacity is paid back as carbon gain; in the shade, it would be wasted. Sun plants have longer palisade cells, often several layers of palisade parenchyma, and therefore thicker leaves as well as a markedly higher weight per unit leaf area. Do these adaptations suffice to achieve higher photosynthetic capacity? Or do sun plant cells even have higher chlorophyll and protein contents than shade plant cells on a volume basis (proxy: mass basis)?

In addition to higher light intensities, leaves in sunny sites are exposed to higher temperatures, dryer air and higher wind speeds. Consequently, they loose more water by transpiration than leaves in the shade, so that sunny sites also require some adaptations to drought. The same is true for sun leaves of forest trees; however, water relations of leaves in the top of tall forest trees, are complicated further because they have to pull up their water over much longer distances than shade leaves further down in the canopy. 

How different are typical sun and shade plants in all these respects? How much plasticity can be expected, that is, how well can sun plants adapt to shade and shade plants to sun? And by comparison, how different are sun and shade leaves of the native light adaptation expert, beech (Fagus sylvatica)? And what role does the relative drought of sunny sites play?

In this course, chlorophyll (a,b) and carotenoid contens of sun and shade leaves are measured by quantitative photometry. Leaf mass per area (LMA), the reciprocal of specific leaf area, is determined from leaf area and mass. LMA is the best indicator for light adaptations and is one of the most important parameters for scaling photosynthesis from individual leaves to entire forest canopies. The anatomy of sun and shade leaves is compared by microscopy of leaf cross sections (e.g. leaf thickness, fraction of palisade parenchyma, cell wall and cuticula thickness). Light response curves of photosynthesis and transpiration of sun and shade leaves are measured by XLAB staff; photosynthesis is measured as CO2 uptake and transpiration as H2O-release by infrared gas analysis using contemporary equipment.

This course is suited for students from grade 10 on and can favorably be combined with the other plant physiological courses. 

Duration: 1 day
Number of Praticipants: max. 20