Seedling growth and light

[sloth]

Maybe a bit of an odd one, my wife and I disagree about how light affects plant growth. I think a seed growing with shorter days will grow taller than a seed growing with longer days while it still has energy in the seed store, then growth will simply slow down; due to less light, giving a plant of x height after a month. She thinks the seed with longer, brighter days wouldn't need to put energy into growing tall in search of light, and so would be thicker and bushier but shorter after a month than 'x'.

I reckon it's light intensity rather than hours of light which affect plant height.

Before I ramble anymore, what say ye?

[Gnome]

I would reckon that the temperature is a more deciding factor than light levels for growth. Once the seed has emerged the amount of degree days( or hours) will decide the rate of growth and yield.

 

A plant grown at 20oC for five hours daylight should show the same growth as one grown at 10oC for 10 hours daylight for example.

 

The fact that in the summer we have longer days usually means we have higher temps this then gives the impression that it is the light that is doing the magic. In the winter the light levels can be still high on good days but if the temperature isn't high enough there will be little photosynthesis as the enzymes etc. won't be able to metabolize.

 

This is a very generalised answer as it would depend on what type of plants you are growing and in what location as C3 and C4 plants have different responses to light levels. Wheat crops v Maize crops.

 

The leaf angle and shape will also determine how much solar energy the plant can utilise. Once light reaches a certain intensity there will be no further benefit to the plant.

 

The rainforest regions are in areas where the daylength is fairly stable all year round and the temperature is warm and humid. Due to weather systems and leaf canopy in the jungle the light levels are not as intense as the desert regions of the world but plants still thrive.

 

I hope that makes sense and hope more learned people can clarify this.

 

 

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[sloth]

Makes a lot of sense, thank you

[daltontrees]

I suspect the answer to this is not simple at all. Perhaps fpor some species the use of seed energy reserves to gain height quickly is a life-or-death adaptation whereas in others the ability to develop photosynthesising capacity very quickly from very little energy reserves (tiny seeds) is everything.

 

Generally growth rate (and I don't mean height, I mean total leaf area) is proportional to temperature but can be inhibited or boosted by respiration which is not so simply proportional to temperature. On top of that there are diurnal cycles that happen, once initiated, regardless of actual light and temperature.

 

To quote from "The physiology of flowering plants" -

 

"... it has scarcely been possible evaluate the effect of any one factor on photosynthesiswithout specifying the status of other factors. The rate of photosynthesis is affected by irradiance, CO2 concentration, temperature, plant water stsus, wind speed and the degree of stomatal opening.The effect of varying any one of these factors depends on the value of the others."

 

So, growth rate is affected by (i) photosynthesis and (ii) the species strategy for converting seed reserves into leaf area, height and other physical attributes. The first is complex, see quote above. The second is complex too and dependent largely on species characteristics. And some plants are predisposed to commence germination at lower temperatures than others and to thrive on short day lengths, and in the case of woody plants to initiate bud-burst at different day lengths. Again I expect it is to do with the circumstances for optimum survival and competition in which the species evolved.

 

So you and your mussus are both right. You could try it next spring, all you need is some pots, a ruler, a thermometer, a sheet of graph paper, some seeds of a variety of species planted in pots every few days.