• Question: Why do plants wither in Winter and not create a protective barrier or something?

    Asked by chloedownes to Amelia, Clem, Izzy, Sarah on 12 Mar 2014.
    • Photo: Isabel Webb

      Isabel Webb answered on 12 Mar 2014:

      In winter, days get shorter and so plants can’t photosynthesise for as long in the day and so can’t make as much energy. It is also colder, and so their chemical reactions happen slower.

      Plants have three options:
      1. try and survive
      2. use energy to try and keep warm
      3. sacrifice their leaves, but use less energy all winter

      It is possible that plants tried the first two at some point in evolution, but that the plants using the third option survived better and so this is what stuck and this is what plants use today.

      Some plants – evergreen ones like Christmas trees – survive all year with their leaves. They have several strategies for this. One is to have needle-like leaves – this reduces the amount of heat-loss by decreasing the amount of leave exposed to the air (in the same way we wear coats and scarves to protect ourselves from cold air).

    • Photo: Amelia Frizell-Armitage

      Amelia Frizell-Armitage answered on 12 Mar 2014:

      You know this is a really good suggestion! However, it would cost the plant a lot of energy to try and grow a protective barrier around it every winter and get rid of this in summer, so this is probably why they don’t do it! It costs the plant less just to lose its leaves and re-grow them ready for spring time.

      However, plants that live in places that are cold all year round like the Arctic do grow a protective barrier! These plants have a fine layer of hairs covering their body which act a bit like a woolly blanket. These hairs can be very long and look like fur see here: http://www.arcticphoto.com/results.asp?image=RC.0154-05&imagex=1&searchnum=0001
      Because it is cold all year round these plants don’t have to worry about shedding and re-growing their blankets, they just have them all the time.

      Some plants that grow in very cold places like the Arctic grow very close to the ground and have very small leaves. This way they manage to trap a layer of warm air around themselves, which in a way acts like a protective barrier but the plant doesn’t have to make it. This is really clever as the plant can save energy and stay warm! The other advantage of being small is that during the winter months the plants are covered by a blanket of snow. Snow is very insulating and being covered in a blanket of it would keep you very warm.

    • Photo: Clemence Bonnot

      Clemence Bonnot answered on 12 Mar 2014:

      Withering is not the only protection again cold that plants have! A lot of plant do not wither.
      Some plant have made the evolutionary choice to live only a short year from spring to autumn. This way their is no need for them to survive all along winter without energy. In the form of seeds they easily pass winter because seeds are very resistant to cold, drought, too much water and just wait the good conditions to germinate.
      Other plant spent winter dormant as a bulb and regrowth from it as soon as sun come out (you have a lot of example of these right now – a lot of daffodils around!)
      In evergreen trees antifreeze is produced by the cells to prevent sap and cellular content to freeze and consequently to break the cells and the vessels of the plants. http://www.forest.fi/smyforest/foresteng.nsf/allbyid/443D3309C379693AC2257C63003D0C79?OpenDocument

      So technically plants have internal barrier or more resistant form to to fight against cold !

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