2 Fine Adaptation

While the main aspects of photosynthesis are the same in all plants, every plant adapts its leaves and its photosynthetic machinery to specific environmental conditions.

The photosynthetic machinery is located inside the leaf cells. The leaf structure protects the photosynthetic machinery from the surrounding environment, but this protection is limited. Since the photosynthetic machinery collects energy from sunlight, it must be exposed to the sun and cannot be shaded. Also, since this machinery must collect carbon dioxide from the air, it cannot be fully protected from wind or dry weather. Some components of the machinery are also sensitive to temperature changes.

Sunlight intensity changes regularly and cycles throughout the day and the year. Wind, temperature and humidity also change, sometimes in an unexpected way. But, most of the time, those changes are expected and can be easily predicted. The range of atmospheric condition that we experience is generally defined by the climate area in which we are located. This climate areas could be, for example, mediterranean, tropical, continental, subarctic etc.

Figure 2.1: Variation of environmental conditions in 2016 in Düsseldorf. [data from http://www.ecad.eu]

To thrive, a plant must manage two different and connected aspects of adaptation:

• Every plant must adapt its leaves and photosynthetic machinery dynamically to ever changing sunlight intensity, air temperature and humidity during the day.

• Every plant species must adapt and finely tune its photosynthetic components in a stable and persistent way to have them performing best at the range of environmental condition that the plant is likely to encounter. Namely the climate or microclimate under which that species evolved.

Figure 2.2: World climate area. Source: Wikipedia.
Attribution: By Waitak at en.wikipedia Later version(s) were uploaded by Splette at en.wikipedia. GFDL or CC-BY-SA-3.0

We scientists at CEPLAS are studying the stable and persistent kind of adaptation. The one that causes every plant species to evolve small structural modification to its photosynthetic machinery in order to perform best in a defined range of sunlight intensity, temperature and humidity.

2.1 Why studying persistent adaptation

We study fine persistent adaptation of photosynthesis for a simple reason – crop plants are often grown in environments and regions that are different from the one in which they evolved. If we understood how crop plants adapted to environment in which they evolved, we would know how they could adapt and grow successfully in a new environment and under new condition. Adaptation and optimization of photosynthesis is considered a path toward growing healthy crop plants with less water and less fertilizers.

To understand adaptation, let’s imagine photosynthesis as a combustion engine² There are many combustion engines, the main concept is similar for all the engines, but every type of combustion engine is adapted and tuned for a specific purpose. You would not move an F1 car engine in a city car, a city car engine in a truck and a truck engine in an F1 car, none of those combination looks like a good idea. And it is too easy to say that one of those engines is better than the others. Every type combustion engine is adapted for a specific purpose and for specific conditions. One should at least know the purpose and the range of conditions for which that engine is optimized.

So does photosynthesis. There are many adaptations of photosynthesis. Photosynthesis is optimized in every plant species for the environmental conditions which that plant has met during evolution and that it is likely to meet in the future. You would not move a model of photosynthesis from one plant species to the other… Or would we?

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2. Photosynthesis is not the same as a combustion engine. If possible, photosynthesis is the opposite of a combustion engine. Whatever an engine “burns”, photosynthesis “unburns”. Our combustion engines today burn very recent and very old products of photosynthesis. Besides comparing photosynthesis to an engine is reductive and it does not convey the wonder that we feel when we observe living organisms. But right now, comparing photosynthesis to a combustion engine can help us understanding adaptation.↩