The energy crisis has caused growers to become more energy efficient and grow at colder temperatures. Victor Boekestein of Reflect4Business looked into the existing scientific literature to see what is already known about cold-resistant varieties and colder growing. Below is a summary of what he researched. For example, who knew that 'anti-freezing proteins' existed?
One possible way to reduce the need to heat greenhouses is to use cold-resistant plants. In this area, genetic modification has already made some progress, Victor discovered.
The group of greenhouse plants most studied for vegetable cultivation consists of several tomato varieties. Depending on the species, with the help of genetic modification, resistance to lower temperatures could be increased by facilitating an increase in the activity of anti-oxidative mechanisms, a study back in 2021 (Cold acclimation and prospects for cold-resilient crops) showed.
Stress factors such as lower temperatures increase the production of reactive oxygen, researchers saw in 2014. In excessive quantities, this can lead to cell damage in plants. Anti-oxidative mechanisms ensure that these oxygen atoms are bound in a harmless way, preventing them from reacting. Another mutant was able to reduce plant cell damage by increasing the activity of the enzyme Superoxide dismutase (SOD) (an example of an anti-oxidative mechanism).
Overcoming teething problems
Light-related damage could also be reduced by increasing the activity of the mechanism of Non-photochemical quenching (NPQ). It should be countered, however, that this modification also produced fewer and smaller tomatoes with fewer seeds, researchers noticed in 2011. So, for now, there are still some teething problems to overcome, notes Victor.
Another example concerns genetic modification to produce anti-freezing proteins, which bind ice crystals so they cannot damage cells. This could achieve a reduction in electrolyte loss of up to 60 percent, researchers wrote in 2021. Electrolytes help plants conserve their mineral balance and support certain essential processes such as photosynthesis and respiration.
For a more concrete picture of what is possible, look at a model plant like Arabidopsis. This plant could be modified such that it could survive a temperature of -8°C (4°C lower than normal).
Another method involves micro-organisms. Arbuscular mycorrhizal fungi (AMF) are the most well-known micro-organisms. These organisms grow on the roots of plants, where the plant provides nutrients, and the AMF provides antioxidants and certain hormones. Those hormones can enhance growth and photosynthesis under less optimal conditions.
Other micro-organisms are rhizobacteria. These also grow on the roots of plants, but they can increase chlorophyll concentration and nutrient uptake, among other things. This ensures better growth of these plants. In addition, they increase the activity of anti-oxidative mechanisms. In tomatoes, for example, symbiosis with Pseudomonas Vancouverensis and Pseudomonas Fredericksbergensis produces less membrane damage. It also increased the concentration of proline and increased the activity of anti-oxidative mechanisms, researchers shared in 2021 following research.
Side effects of colder greenhouse
The side effects of a colder greenhouse should also be considered, Victor believes. He came across studies addressing this even before the outbreak of the energy crisis. Lower greenhouse temperatures have side effects, which can (partially) negate some of the positive effects of a colder greenhouse.
A first side effect of a colder greenhouse is a reduction in water and nutrient uptake. This leaves more water and increases humidity, which can cause problems with diseases such as Botrytis. Using less water can reduce the risk. The amount of nutrients should also be adjusted to reduce uptake. Humidity can be further controlled with ventilation and (just) enough heating to prevent condensation.
The second side effect flows from the first, researchers wrote in 2015. A colder nutrient soil increases the risk of root rot caused by Pythium, Rhizoctonia, and Thielaviopsis. This will require the application of fungicides, which, however, work more slowly due to the colder soil.
Slowing down the life cycle
A third side effect is somewhat more positive. A colder greenhouse slows down the life cycle of many insects and mites. Researchers saw this in studies back in 2020 and 2015. So in the early stages of plant growth, less treatment will be needed. It will then be more convenient to introduce pollinators later as well, although bumblebees can fly as early as 6°C. During the warmer spring, on the other hand, insects can make their appearance quickly, so the respite is short-lived.
The final side effect plays into the temperature difference. A colder greenhouse provides a smaller temperature difference (between day and night temperatures), so plants cannot grow as quickly. This is, therefore, where genetic modification can help.
The effect of colder greenhouses can lead to a reduction in energy consumption, saving money. This can be achieved by making plants more resistant to colder temperatures. This can be done using genetic modification and diversifying the micro-organisms which live in the nutrient soil. In the latter case, it can also help protect the plants from diseases using rhizobacteria. The effectiveness of this method depends a lot on the plant and the micro-organism.
The colder greenhouse also comes with unforeseen costs in the form of increased risk of diseases and reduced growth. In contrast, the colder greenhouse also provides unforeseen benefits in the form of less water use and fewer insects in the early life stage of plants.