How do conifers keep their green needles over the boreal winter?
During boreal winter most trees shed their leaves. However, conifers such as Christmas trees keep their green needles intact. Scientists believe that a phenomenon called sustained quenching offers photoprotection and enables their survival, but its precise molecular and physiological mechanisms are not understood. Researchers have now found that the photosynthetic apparatus is wired in a special way which allows pine needles to stay green all year long.
In winter, green chlorophyll molecules harness light energy, but that energy cannot be used in the photosynthetic machinery as very low temperature halts most biochemical reactions. However, in early spring, even as temperatures are low, there is plenty of sunlight. The excess light energy can damage the photosynthetic machinery’s proteins. Under normal conditions, the two photosystems, the two functional units where light energy is absorbed and converted into chemical energy, are kept apart from each other to prevent a shortcut and allow efficient photosynthesis. According to a study published in Nature Communications, a team of researchers found that in winter, the two photosystems are brought in physical contact with each other through reorganisation of the structure of the thylakoid membrane, where the two photosystems are located. Photosystem II donates energy directly to photosystem I and this short-cut mode protects the green chlorophyll and the needles when conditions become harsh.