Seasons and Sefton

In temperate regions such as the UK, our ecosystems experience seasonal dynamic fluctuations, as our moderate climate slowly fluctuates throughout the year. These fluctuations follow an annual trend, with many species of tree blossoming in spring before shedding their leaves in an impressive colourful autumn display leaving just bare branches through the winter days. In sync with this, animals appear to breed as temperatures increase yet hibernate through cooler days.

For those of you living in Liverpool, student or otherwise, it is well known that Sefton park is one of the most popular places to visit for its aesthetic beauty. I have lived in Liverpool for 4 years and have always been intrigued by the ecosystems it has to offer. Here I have documented how the park changes throughout the year by capturing photos at four different occasions between September 2016 and May 2017:

September 2016
November 2016
March 2017
May 2017

The science behind these changes is fascinating. One of the most noticeable differences observed in the park can be seen in the trees, specifically in how their leaves reflect the fluctuating seasons. Throughout the winter months, trees enter a period of dormancy in order to survive the low temperatures. However, despite their stark dormant appearance, deep within their branches they are actually busy maintaining themselves through respiration and enzyme synthesis and preparing for the coming spring.

As spring approaches, these trees begin to bud leaves and flowers, a change brought about in response to an increase in temperature and light availability. Throughout the summer months, different shades of green dominate the park. It is the photosynthetic pigment chlorophyll which gives leaves their vibrant green colour. This pigment enables plants to absorb energy from sunlight, specifically, it absorbs light in the blue and red portions of the electromagnetic spectrum while reflecting the near-green portion, therefore producing the vivid shades of green we see throughout the summer.

The breakdown of chlorophyll in the autumn reveals carotenoids in the leaves causing them to change from green to yellow/orange and creating a variety of colour throughout the park. Eventually, leaf abscission occurs.
Leaf abscission refers to the controlled process by which trees shed their leaves. This occurs from the Abscission zone (at the base of the leaf’s stem). Abscission zone cells differentiate in early plant growth and are able to respond to a number of environmental stressors and plant hormones. When light levels start to reduce and chlorophyll is degraded, levels of the plant hormone auxin decrease which in turn increases sensitivity in the abscission zone to another hormone ethylene. When the plant is exposed to ethylene cell wall-degrading enzymes such as cellulase and polygalacturonase are activated and abscission occurs.The trees then enter dormancy and the process repeats itself. There is a clear seasonal regulation of growth. And, it’s not only trees which follow this cycle, other flowering plants also respond to changes in seasons and sunlight which, in turn, allows many insects and mammals to thrive building a complex and beautiful ecosystem around these plants.

The images included in this article provide a visual representation of how our planet constantly changes. Sefton provides city dwellers with the ability to witness these changes first hand throughout the year – and we can guarantee you a mystical view on whatever day you decide to visit.

Take home message: Next time you take a trip to Sefton, have a look at the forever changing ecosystems and think about the biological processes occurring beneath the visual changes.

Post by: Alice Brown:

References
http://www.journals.uchicago.edu/doi/abs/10.1086/283724?journalCode=an
https://link.springer.com/chapter/10.1007%2F978-94-011-4453-7_45#page-1
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1087143/pdf/plntphys00512-0027.pdf
http://postharvest.tfrec.wsu.edu/pages/PC2000F
http://scienceline.ucsb.edu/getkey.php?key=1110
https://www.ncbi.nlm.nih.gov/pubmed/17737985

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