How Conifers Stay Evergreen

Conifers such as spruce and pine, essential symbols of the festive season, are adapted to thrive in some of the planet’s harshest conditions. Found predominantly in boreal forests, these trees withstand freezing temperatures and intense sunlight, maintaining their green needles year-round. Recent research, published in Trends in Plant Science, sheds light on their survival mechanisms, particularly unique adaptations in photosynthesis.

Photosynthetic adaptations during winter

Photosynthesis, the process plants use to convert light energy into chemical energy, typically follows a conserved mechanism. However, conifers exhibit distinct strategies that allow them to endure winter extremes. Two critical adaptations have been identified by researchers at Umeå University and collaborators:

1. Spillover mechanism

In winter, conifers alter the structure of their thylakoid membranes, which house Photosystem I (PSI) and Photosystem II (PSII) – the protein complexes involved in photosynthesis. Typically separate, these complexes move closer together during cold seasons, enabling a process termed "spillover." This interaction allows excess light energy to be safely dissipated, protecting the photosynthetic machinery from damage caused by excessive sunlight during freezing conditions.

2. Alternative electron flow

Conifers also use alternate pathways for electron transport during photosynthesis, involving specialized proteins called flavodiiron proteins. These pathways help maintain the balance of the photosynthetic process and prevent system overload, which can occur when light intensity is high, and temperatures are low.

Structural differences with flowering plants

Conifers differ from flowering plants in their photosynthetic composition. For instance, they lack certain light-harvesting proteins found in angiosperms. These structural variations, coupled with their unique adaptations, contribute to their dominance in boreal ecosystems. However, this specialization may come at a cost – conifers are less competitive in more temperate regions where water, nutrients and favorable temperatures are abundant.

Ecological implications

Conifers' remarkable adaptations ensure their survival and ecological dominance in boreal forests, which are critical carbon sinks and biodiversity reservoirs. Understanding these mechanisms may aid in predicting forest responses to climate change. In the long term, such insights could inform strategies for developing crops resilient to extreme weather, potentially mitigating the impact of global climate challenges.

“All together this can explain why conifers are the dominant species in boreal forests, thriving where few others can, perhaps at the expense of advantages during less challenging conditions; few conifers, if any, grow where water, nutrients and temperature conditions are all favourable”

Dr. Pushan Bag

Reference: Bag P, Ivanov AG, Huner NP, Jansson S. Photosynthetic advantages of conifers in the boreal forest. Trends Plant Sci. 2024:S1360138524003005. doi: 10.1016/j.tplants.2024.10.018

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