Saturday, January 1, 2011

Green Roof Plants - Frost Damage and Photosynthesis

Welcome to 2011.  We look forward to kicking off the new year with interesting articles and discussions about green roofs.

Two of the areas we will be focusing on this year are:

A.  Roofs for permaculture and feeding the world, and
B.  Native wildflower and native plant green roofs irrigated by nature alone (dew, fog, rainfall)

The two are somewhat diametrically opposed as one requires higher nutrient and irrigation input using a variety of non-native food species.  The other focuses on native plant species, their soil organism relationships and natural irrigation in the spirit of water conservation.

Every day is a new educational opportunity for learning about green roof plants.  As we study rooftop permaculture and nature based green roofs we will be trying to first understand the difference in a basic plant physiological process, that of photosynthesis.

There are three basic types of photosynthesis processes that occur in plants and they are termed "C3", "C4", and "CAM".  We will be discussing the differences in future articles but in general, the majority of the world's plants are "C3" plants.

C3 plants conduct photosynthesis directly at and beneath the leaf surface in cells called mesophyll cells.

Frost on Green Roof Plants

In C4 and CAM plants photosynthesis occurs in a different manner with different cells - we will discuss those in future blogs.  Understand now though C4 and CAM plants may use a combination of different cells, some deeper in the plant and plant leaf for photosynthesis.

As mentioned, in C3 plants photosynthesis occurs generally on the leaf surface or just beneath the surface.  Remember, stomata are the openings in the leaf allowing for exchange of gases - intake of CO2 and output of O2 and on the C3 plants stomata can be found widespread across the leaf.

The proximity of the photosynthesis process and numerous stomata on the C3 plant leaves create a situation where the plant's vital photosynthesis process is more exposed to the climate and elements.  C3 plants may sometimes quickly loose water and become desiccated due to hot temperatures or strong winds.  Also the leaf's photosynthesis process and cells may be susceptible to frost damage.

The above photo is of frost on green roof plants.  Examine the frost crystals and you can see they are sharp!  As water vapor freezes before fully evaporating, frost crystals form.  The formation of frost crystals may damage photosynthesis responsible mechanisms within the leaf and injure or kill the plant.

There is a place for all types of plants on green roofs, C3, C4 and CAM.  Understanding the processes and nature of each are important to the green roof designer.

Over the next few months we will be examining many of these plant differences.

Happy New Year and Happy Green Roofing!


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