We all know that Sempervivum are tough plants given the right conditions, which leads to the question, what are the right conditions?
To answer this question there have been many experiments done with these tough plants to find out how they grow. My goal here is to explain some of the findings so we may understand our Sempervivum better. Heat, light, temperature all factor into how semps breathe, take in nutrients and grow. So my first post will be some definitions and some basic simplified plant physiology explanations, and I will edit and add to this post as time allows
Before I start I just want to say I am not a plant biologist, just a gardener who likes to know how things work so If someone more knowledgeable knows something thats not correct, feel free to point it out. The goal here is to help everyone understand their plants better. Feel free to tree mail me with opinions, changes or corrections!
Some definitions to start:
Stomata are the tiny pores in plant leaves that allow for gas exchange. They are usually found on the underside of plant leaves.
Photosynthesis is the process by which plants and other things make food. It is a chemical process that uses sunlight to turn carbon dioxide and water into sugars the cell can use as energy. A byproduct of photosynthesis is oxygen.
There are 3 ways that plants can convert light and CO2 into the sugars and carbohydrates needed to grow, but for our Sempervivum, only 2 of these ways are of interest to us. Here is a basic very simplified explanation of each.
C3 photosynthesis is the pathway that most plants use. C3 plant take open their stomata during the day, take in CO2. Using light energy they split off the hydrogen atoms from a H20 or water atom and combine the hydrogen and carbon dioxide into the sugars and carbs needed for growth. They give off oxygen as a byproduct. If there is a shortage of CO2 or water growth stops. This type of photosynthesis uses alot of water, because having the stomata open all day during the hot part of the day, causes the plant to lose alot of water due to evaporation. Most lawn grass and trees use this type of photosynthesis.
Crassulacean Acid Metabolism or CAM photosynthesis is what most succulents including Sempervivum use(most of the time). It differs from C3 in that CAM plants open their stomata take in CO2 at night and the cool parts of the day and store it in special cells. This allows them to close their stomata during the heat of the day to conserve water. The CO2 is stored in special cells as an acid, which is broken back down and the CO2 used during the day for C3 photosynthesis. It prevents water loss during the day, which allows CAM plants to be much more water efficient, but because they only take in CO2 at night and the very first part of the day, once it is used up growth stops, or they may open their stomata back up later in the afternoon to take in more CO2, so in general CAM plants are much slower growing. How much CO2 is used and when stomata are opened and closed for CAM plants to take in more CO2 are dependent on temperature, daylength and light levels. CAM photosythesis allows succulent plants to function is desert and alpine conditions with hot dry days and cool nights where other plants would wither and die.
As a final thought plants do have respiration. Plant cells still need oxygen to breathe just like you and I and when they breathe they give off CO2, but these amounts are much smaller than the photosynthetic process of converting CO2, water and light into sugar and giving off O2 in the process.
