It just occured to me that I had no clue about how trees “know” it’s time to grow leaves, flowers, etc…in the spring. Light? Temperature? Something else?
I always thought it was sustained temperature, but after a certain cycle had also occurred.
I am not a botanist.
Depends on the species.
As far as breaking dormancy, in some it’s day length, in some it’s temperature, in some it’s the amount of water in the soil, in some it’s a simple count of the number of days since the trigger for them to shed their leaves. In most species it’s a combination of several cues, for example they need a day length in excess of 8 hours *and *temperatures above freezing. Either on on its own won’t work.
Perhaps surprisingly, temperature is the least common trigger, but that makes sense. It would be fatal for a plant to expose its growth apexes by producing new leaves in response to a few warm days in late winter or autumn, only to be hit by a hard frost the following week. It’s much safer for a plant to reshoot only when the temperatures are certain to remain above freezing, and the only way to be sure of that is to either wait for the ground to thaw fully or wait for a specified period of time.
Flowering in most temperate species is primarily day length dependent. However here too there are usually other factors which will suppress the response, such as a lack of nutrients or water. Basically if the plant is healthy , it will flower when the length of day:night is correct. If it’s not healthy it can suppress the response. For tropical and subtropical species the cues are much more variable, and depend on soil moisture, temperature and damage in addition to day length.
Trees, after experiencing a minimum number of hours of cold, a chilling requirement, during a process called Vernalization - the acquisition of a plant’s ability to flower or germinate in spring season by exposure to the prolonged cold of winter - are signaled to begin growing by Spring’s warming days. They are not triggered by quality of light, nor the lengthening of the days, but rather the warming that the brighter, warmer days bring on.
Some herbaceous plants do depend on photoperiodic response, the lengthening of the days. They do this with a light sensitive pigment called Phytochrome, which is destroyed by light and is accumulated during the plant’s dark cycle.
When the phytochrome no longer accumulates in sufficient quantities, the night being too short for more to accumulate, this phenomenon allows plants to “sense” the lengthening of the days and flower (examples snapdragons, spring bearing strawberries.)
This sentence “They are not triggered by quality of light, nor the lengthening of the days, but rather the warming that the brighter, warmer days bring on.”, doesn’t quite make sense, meant that there is no particular springtime spectrum of light involved that brings about the break in dormancy, and there is no photoperiodic response for deciduous trees. The number of warm days needed, like Blake said, is dependent on the particular species.
Cite. Seriously, can you provide a reference for this, because it directly contradicts the word of some of the most eminent plant physiologists in the world.
Compare for example:
"The buds of plants expand, flowers are formed and seeds germinate in the spring - but how do they recognise spring? If warm weather alone were enough, in many years all the plants would flower and all the seedlings would start to grow during Indian Summer, only to be destroyed by the winter frost. The same could be said for any one of the warm spells that punctuate the winnter season.
<Snip several sub-chapters dealing with the multiple factors that break dormancy, including endogenous inhibitors, day length, soil moisture, temperature (both air and tissue) and so forth.>
There does not seem to be any common mechanism by which dormancy is induced or broken. This fact, although it considerably multiplies the problems of the plant physiology is, is certainly in keeping with our sense of evolutionary history. Dormancy became advantageous to plants relatively recently, when the seeds began to spread into a variety of different ecological domains, Presumably dormancy evolved independently on many groups of plants, each of which found its own solution separately among the survivors, often in a different way."
Peter H. Raven 1998. “external Factors and Plant Growth” in “Biology of Plants 6th ed.”
So can we please have some evidence for your bold claim that dormancy is never broken by day length, and is only ever broken by increase in temperature.
I await your response with eagerness.
Really? Can we have a cite for this? Because
“bud break of Celtis, Quercus and Fagus growing in warm climates is induced in early spring by increasing daylength.”
Rolf Borchert, Kevin Robertson, Mark D. Schwartz and Guadalupe Williams-Linera, 2005
“Phenology of temperate trees in tropical climates” International Journal of Biometeorology
and
“exposure to a 13-h photoperiod induced bud break of dormant apical buds in
saplings and cuttings [of potted saplings of Plumeria rubra] in January, whereas plants maintained in the natural day length of < 11.7 h remained dormant. Photoperiodic
control of endo-dormancy of vegetative buds in stem succulents is thus supported by field observations and experimental variation of the photoperiod. At low latitudes, where annual variation of day length is less than 1 h, bud dormancy is induced and broken by variations in photoperiod of less than 30 min.”
ROLF BORCHERT and GUILLERMO RIVERA, 2000. “Photoperiodic control of seasonal development and dormancy in tropical stem-succulent trees”. Tree Physiology
So can we have some evidence for this repeated claim that “there is no photoperiodic response for deciduous trees”, since it flatly contradicts the most eminent plant physiologists published in the best journals.
I am very interested in reading more of this, Blake.
Am curious to learn what mechanism might be responsible for the photoperiodic response. Could it be phytochrome? I want to read more of the first article, all of the species mentioned I am familiar.
But at any rate, no one can deny some years trees leaf out later than others, and this can be easily be correlated with temperatures. After all, does the daylength progression vary from spring to spring? Here where the cherries are plentiful, some years when we get an early spring in the form of a sufficiently long streak of above average temperatures, the trees come out of dormancy earlier than average putting them at particular risk for any late frosts. If the weather stays cold, the trees will wait - regardless of daylength.
I must say though this is a tropical tree, does not grow in the temperate zones.
Thanks Blake, am curious about learning more, esp the first link, would like to read the article.
Nothing to do with the case.
So you made these absolute claims that trees only ever break dormancy in response to temperature, and that they never ever break dormancy in response to day length.
And when you are asked to provide evidence, you can provide none. As I thought, you have no idea what you are talking about.
Suffice it to say, the references prove that you are absolutely wrong. Trees break dormancy in response to multiple factors. Most individual trees break dormancy in response to multiple factors. It is indisputably not just temperature as you claim. Photoperiod plays a role, as does the time since the inducement of dormancy, soil moisture and various other factors.
But of course I said all this in my first post.
What I claim is that if the trees have had a sufficiently long dormant period, and then subjected to a sufficiently warm spell, things will start to grow. Your second reference is for one single plant, your first reference is a general statement that provides no specifics whatsoever. It does not prove anything.
Where have you honestly been all your life Blake that you have not observed the variance of spring, and how warmth plays a role? What highfalutin scientific paper can you refer to that demonstrates what can be easily observed year after year - that the woodlands come out of dormancy depending on the warmth of the weather? Since your posts drip with accusation and bbq tone, I kindly suggest you put some of the studies aside once in a while, and actually get outside and see what the heck is going on with the trees and the weather. The photoperiod/daylength is the same every April1st, Blake. Every year it is the same, save for a mere fraction. Yet any given year on that date, the woodlands will be responding to the temps they’ve been exposed to in previous days/weeks, some years they will be further ahead than other years, some further behind - and why there is a variance of this progression - regardless of the day length. I am not saying that there are not other minor factors that come into play but they play a minor role compared to warmth.
Soil moisture content is also a trigger, as Blake noted above. This may be strongly correlated with temperature history each spring, but that doesn’t mean that the plants are actually sensing the temperature. To differentiate between the two possible mechanisms, you need the laboratory experiments.
Is my understanding right in that some species measure day length and others measure night length? (In practice this only matters when artificial light or other very unusual disruptions are around).
Can I say I’m more interested in the battle between Blake and the lone cashew than the actual answer. What would be even better is if one is a sock puppet for the other.
This is all completely and utterly wrong.
The fact that he is completely unable to provide references for any of this nonsense, and the fact that it is directly contradicted by the references I have provided is really all that needs to be said.
If anyone else wants to discuss this subject, I’m more than happy to do so. But I’m through with the lone cashew on this topic.
Willful ignorance can not be fought.
Are you saying that temperature is not a factor also? Because you included it in your previous post:
So, both of your are saying temperature is a factor along with other factors (multiple simultaneous) - but cashew is completely and utterly wrong.
Please explain.
Here’s some research showing variability in average flowering time correlated with temperature:
I think it’s pretty obvious that there are a variety of factors. Seeds underground can’t tell how long the day is, and yet they sprout in the spring, so that must be temperature-driven (although I’m fascinated by someone’s claim that they actually count the days). But, as several have noted, trees that put out leaves during a warm spell in December will likely be sorry.
A semi-related topic that occurs to me is the Creationist/ID mantra, “What good is half an eye.” The various responses of plants to light show that even the most primitive forms of sensitivity to light can give an evolutionary advantage.
Not even close. Cashew is saying that temperature is the *only *factor for *all *trees. He is saying that nothing else matters. He is saying that day length has no effect whatsoever, that all that a tree needs to break dormancy is the correct temperature regime.
That is a load of horseshit. Temperature is *one *factor for a *minority *of tree species in a *limited *area. Temperature is not the sole factor for any species. It is certainly not the sole, or even primary, factor for all species. And even for most of those species in which it is a factor, it isn’t a factor over most of their rnage.
His claim that “if the trees have had a sufficiently long dormant period, and then subjected to a sufficiently warm spell, things will start to grow” is horseshit.
If some individual trees, in some species, in some locations, have had a sufficiently long dormant period, and then subjected to a sufficiently warm spell, nothing will happen unless those trees also experience the correct day length, or the correct number of days since the induction of dormancy or the exposure to triggers, or sufficiently high soil moisture or multiple other causes.
In no sense is what he claims true. It is completely and utterly wrong, which is why he is unable to produce even a single reference to support his claims, and why every reference I have provided states outright that he is incorrect.
When Prof Raven says outright “It is not, and can not be, just temperature” and some anonymous contributor on the internet says “It is always just temperature”, where do you think the truth lies?