Monday, 22 December 2014

Fagus sylvatica

Just a wee taste of summer today as we are in the shortest days of winter. This is the common beech, Fagus sylvatica, photographed at the end of April 2014. The leaves are expanding from their tiny concertina form through the heavily folded young leaves to the fully expanded mature form. Looking at this photograph, I can feel the sunshine and the anticipation.

At the other end of the year, the photograph below shows the same plant with the leaves in their winter form. Although they are now crisp and entirely dried out, they are equally attractive with bronze colouring and a neat pattern of veination.

Merry Christmas, wherever you all are!

Wednesday, 10 December 2014

How dark is it?

I've been trying to measure light intensity to get a clearer idea of how much variation there is in different plant growing environments. I'm going to take measurements in a number if different situations and list them here just for interest.

To understand how the photos were taken please see the page on measuring light intensity with a digital camera.

Some measurements:

March in Cambridge:
1/80th second exposure

December in Cambridge:
1.3 second exposure

Night time, with street lights,
in December in Cambridge:
30 second exposure

Indoors, after dark. 
8 second exposure

Saturday, 6 December 2014

Euphorbia and frost tolerance.

This is a Euphorbia plant showing plant frost tolerance at its best.When I took this photo the temperature was about -3 degrees C and everything around was very frozen, including my fingers. 

Some plants are able to tolerate a lot of freezing, and when the weather warms up, they carry on exactly as before, and looking as if nothing had happened. This Euphorbia is a good example. 

Some plants are not frost tolerant at all. I discovered this first-hand once when my plant growth room became confused by a heatwave outside and turned into a freezer inside. For a few hours the Kalanchoe plants inside looked like frozen versions of themselves, but when the room warmed up again they turned to mush. 

As I understand it, this is because the water in their cells had frozen into shards of ice and punctured the cell walls. In their normal state, plants are like massive structures made entirely from water-filled balloons. The little balloons are the tiny plant cells. If a plant has no frost tolerance mechanism, then in a good freeze, the ice shards will pop all of the little balloons that make up a plant's structure. When the water thaws again there is no structure to hold the plant up, and the whole thing just melts down to mush. 

Some plants, like the Euphorbia above, have mechanisms to prevent the cells from being popped. Scientists call these processes "cold acclimation". 

Summarised in a recent-ish paper (Hannah et al., 2005), it seems that plants are invoking a whole lot of different schemes to keep their cells safe during the coming frost. Plants are turning the expression of hundreds of different genes on or off, or up or down. Consequently, a whole range of activities in the plant are altered. Growth changes, and the cell walls are adjusted to make them more able to withstand the different challenge of cold weather. Salts and water are moved around to different locations in the plant. As I understand it, this is for safer storage of the water, as it might puncture cell walls if it was allowed to freeze in the wrong place, or in the wrong way. Lastly the production of antioxidants goes up, though I'm not clear on why that is or what it does. 

The real message for me is that cold acclimation is not just one single technique, or even five different techniques used by five different families of plants. It is a hugely complex system with many different layers of activity going on. 

The other interesting point is that these processes seem to occur when the plant starts to feel a bit chilly, in preparation for the actual freeze to come. This means that if we take a frost tolerant plant from a warm place, and plunge it into freezing temperatures without warning, then it might not be nearly so happy about the situation. There's a warning in that for those of us who buy plants from warm shops and take them straight home to the garden. 

So there we are. That's a little foray into the world of cold acclimation. As the winter weather ramps up this year, we will know that apparent inactivity of our garden plants is really just a graceful front. The plants have it all going on inside, as they get ready to glide effortlessly through another winter. 

Monday, 1 December 2014

Plants, light intensity and the camera

 Gardening and photography have rather a lot in common, in that they are both very dependent the availability of good light.

Plants grow best when they have plenty of light and cameras produce their best photographs under the same sort of conditions. If there is not enough light, plants become yellow and elongated, and cameras produce photos that are fuzzy or too dark.

In gardening there is always a lot of discussion of the business of "enough light" but rarely any clear definition of what constitutes "enough". There are phrases like "full sun" and "partial shade" but these refer to the number of hours in the day during which a given area of the garden will be bathed in the maximum available sunshine. This takes no account of the strength of sunshine available, which may vary significantly depending on the time of year and the location of the garden.

So here's a question: Can we measure the intensity of sunlight using a digital camera? I don't mean with a level of accuracy that runs to the nearest photon. What's needed here is just accuracy sufficient to support meaningful discussion of gardening conditions between people who may live in very different parts of the world. For example, could a gardener in Egypt describe his gardening conditions to a Canadian gardener by using his digital camera to take measurements of light intensity?

I've been experimenting with this a bit and here's one of my first attempts.

This photo was taken at the end of spring (29th March) with the following parameters:

1/80th second exposure

The photograph below was taken with the same camera, lens, and location, but on the first day of December, of the same year. 

1.3 second exposure

So can we calculate the difference in light intensity based on these parameters? To make it easier I have taken the second photograph using the manual setting on the camera, and I have set the ISO and aperture to the same levels as in the first photograph. 

I had to use a tripod to take the photograph, as the only paramater I wanted to vary was the exposure length. I ended up needing quite a long exposure, which would have introduced a lot of camera shake without a tripod. 


The answer is - Yes! It's actually pretty easy to make a direct comparison of light levels using a camera. However, it really helps if the same model of camera and lens is used to measure both samples, and it really very much helps if the camera has a manual mode to enable some parameters to be kept constant between both tests. 

The bottom line though, is that if you want to talk gardening with your distant friends, even friends who may currently be in a different season (perhaps Australia versus UK) or in a different latitude (e.g. Northern Scotland versus Botswana) then it's pretty easy to do it. 

I don't think we need to worry about expressing light intensity in Lux, or photons or anything tricky like that. As gardeners we could probably stick to expressing it in seconds of camera exposure time, on the understanding that all other parameters are kept the same between our location the location for comparison. 

The next question is to ask how this works with different models of camera, but that is a whole other thing. A question for another day I think. 

An add-on - 

MaryWilliams @PlantTeaching on Twitter has suggested that this work might also be done using a smart phone app. I've had a quick look online and it seems that there are already a number of light meter apps available. If you try this, please do write and let me know how it goes. I will compile the results from different locations. 

Good luck!