Maximizing Photosynthesis: Here Comes the Sun (with help from beetles, not the Beatles)
Leave no stone unturned! Or sun unused, as the case may be with syntropics. The second tenet, maximizing photosynthesis, is perhaps the simplest. Don’t make the mistake, however, of believing that because it is simple, it is unimportant. Photosynthesis is the most important biochemical process in the world. And yes, that is a hill I will die on. Photosynthesis is what makes this planet livable; it vents oxygen into the air as a byproduct, removes toxic carbon dioxide, and is the bedrock of our food systems. In short, photosynthesis is magic. Luckily for us, it is the type of magic that can be understood and explained. In this upcoming section, I will take you on a journey through photosynthesis, and then explain how this tenet works in agricultural practice.
For some reason, in all my years of learning science, I have always been taught photosynthesis in October. This has led to me thinking about photosynthesis as a haunted house of sorts. Photosynthesis begins with a tiny particle of light hitting a leaf. Or as I like to think about it, a very excited kid entering a haunted house. The kid has a ton of energy when entering the haunted house, and may put up a brave front. However, as soon as it is time to enter the haunted house, the kid loses his bravery and becomes scared and apprehensive. He becomes, in essence, a different person (or at least a different haunted house customer). The same thing happens when light hits a leaf. Just as the haunted house scares the kid into a different person, the leaf transforms the light particle into a chemical particle. But how does this process happen?
All light particles have energy…kind of like a kid waving his hands in the air in excitement. Kids can’t run into the outside walls of the haunted house and get in though; they need to find a door. Light does too. On a leaf, this door is called a reaction center, and they are equipped with special, microscopic parts of plants called an antenna system. Just like a scary banner proclaiming a haunted house would draw in kids, an antenna system captures light and draws it into the reaction center of the leaf. The reaction part of the leaf is the same as an entrance room in a haunted house. When the light particle hits the leaf, this energy excites other particles in the leaf, very tiny particles called electrons. Imagine the hand-waving kid running into the haunted house, and then suddenly stopping in terror, only to have an ax-wielding actor run at him. Viewed from a photosynthetic point of view, that actor has absorbed the kid’s energy. Or in a leaf sense, the electron has observed the energy of the light particle. Now, the electron (or ax-wielding murderer) has all the energy. Where does she go from here? To other rooms of course! All who enter the haunted house must be scared. These customers the ax-wielder is scaring are not light particles, however. That kid got scared in room one and left. No, these customers are the hardier teenagers, who stuck it out past the entrance and are milling in rooms on one side of a hallway. Or, in a leaf, these are hydrogen atoms, hanging out on one side of the internal barrier near the reaction center. The ax-wielder moves from room to room, looking for someone to scare, and these teenagers flee across the hallway, to rooms on the other side. In a leaf, that ax-wielder becomes an electron, moving through a series of reactions in the electron transport chain. As the electron moves from station to internal station in the leaf, the energy it carries is used to move electrons from one side of the barrier to the other. Just as the teens prefer to be on the less scary side of the hallway, and are forced into the other side by our lovely ax-murder, the hydrogen atoms prefer to be outside the barrier and are forced inside by the energy of the electron.
As the ax-wielder comes to the end of the hallway, she is exhausted. The hallway is pretty long, and she has been sprinting after way-ward teens all night. What she needs, is a ride. Then, how lucky! At the last room, a designated ax-wielder picker-upper is here to sweep her up and away to her next engagement. Similar to the ax-wielder picker-upper at the end of the hallway, the electrons have an electron acceptor that they go to after the end of the electron transport chain. But what happens to the teenagers (or hydrogen atoms)? They are still trapped on the other side of the hallway and are desperate for a way out. They search and search, and at long last find a door. It will not open. Becoming gradually more and more frantic, the teens bang on the inside of the door, their voices hoarse and strained, the hands bruising as they push with desperate force. It will not open. Tears, snot, blood from broken fingernails as they claw at the unmoving barrier in front of them; the smell of despair is tangible. It will not ope…opps, jk. It opened. The owners of the haunted house were waiting until a crowd of people was walking by, hoping to pique the interest of other customers by demonstrating just how scary the haunted house truly is. The teens pour through the door, streaming out into the night. The owners’ scheme has worked. Other people, seeing the terror, know that this is a good haunted house, and get in line. By waiting until other customers were nearby before opening the door, the owners have made more money.
In photosynthesis, the “door to the outside” is called a hydrogen pump. The hydrogen atoms, just like the scared teens, really want to be back outside the barrier they were forced across. The hydrogen pump provides a way out, and just like the owners harness the teens to make more money, the cell harnesses the energy of the hydrogen atoms streaming through the pump to make energy in the form of ATP, by forcing an additional phosphate onto a molecule that only has two phosphates. A phosphate is a group of atoms. ATP is a common form of energy currency in cells, much like cash is in society. Plant cells then use ATP (along with other things like carbon dioxide) to make food for themselves. And in the process, food for humans! But it all comes from one little particle of light.
That is precisely why farmers are so concerned with plants getting the right amount of light-too little light, and the plant will die, just as a haunted house would with no customers. In syntropy, this means that plants must be selected very carefully. If plants had to compete with others for light, it will be harder for them to grow, just as a haunted house would find it harder to attract customers if there was another haunted house in the area.[1] In order to avoid that, syntropic managers must always think about the light requirements of different plants and must avoid planting together plants that would compete. In practice, this sounds simple, but it often involved complication planning and preparation. This is also part of the tenet “stratification”, which will be discussed next week. In the meantime, I hope that you all look at plants a little differently, after having learned of the complexities it takes to make energy from sunlight. After all, if you had a haunted house inside you, I’d bet you’d be super uncomfortable. And they do this complicated process every single time the light shines on a leaf. So please, say “thank you” to a plant today.
With appreciation for haunted houses,
Ajah Eills
[1] Hautier, Y., Niklaus, P.A. and Hector, A., 2009. Competition for light causes plant biodiversity loss after eutrophication. Science, 324(5927), pp.636–638.
