while not actual scientific papers/experiments, it is some more personal experiences:
http://www.islandnet.com/~tmalcolm/aquacult.html
"Aquatic Utricularia love warmth! However for a variety of reasons such as algal and bacterial blooms at high temps, and dormancy, the best range would be from between 20-25°C. Below 18°C, and the plants begin developing turions. I have experimented with U. macrorhiza, and have found that temperature and not photoperiod is the key factor to turion production. My personal experiences with other temperate species suggest the same. I would think that tropical species would do poorly indeed below 18°C, and would perhaps die at 15°C."
An I hesitate to post this one, because I am firmly NOT a believer in (man-made) global warming!
but..ironically it does kinda prove my point!
(it seems warmer average temps, from year to year, are causing trees to break dormancy earlier..for the sake of this thread, we will ignore the topic of WHY global temps are increasing!
totally different topic!
but..regardless of the reason, its obvious that warmer temps earlier in Spring = earlier dormancy break and flowering..photoperiod is unchanged.
has to be ONLY the temp doing it! the photoperiod CANT change!
http://www.audubonnaturalist.org/feat0600.htm
and more:
http://www.blythe.org/nytrans...._Plants
Ah! here is some good info..
this says photoperiod is more important when *entering* dormancy..and warmer temps are more important when breaking dormancy:
"DAYLENGTH
The main environmental signal which triggers the onset of dormancy is daylength. For most temperate woody plants, long days promote vegetative growth and short days trigger dormancy. As days begin to get shorter in later summer growth slows, and eventually a dormant bud develops. You may recall from an earlier biology class that it is actually the length of the night that is critical, not the length of the day. Short nights stimulate growth, long, uninterrupted nights stimulate dormancy. Daylength of course is a very reliable environmental signal since it is perfectly stable from year to year and trees will not be tricked into growing longer because of an abnormally warm fall. Daylength then is the primary trigger that results in the changes in growth regulator production which in turn results in dormancy development. The growth regulator abscisic acid (ABA) apparently plays a role in dormancy development and has been found to build up to high levels in the fall.
INFLUENCE OF TEMPERATURE
Decreasing temperatures also play a role in dormancy development. Short days cause the plant to enter pre-dormancy (and maybe even true-dormancy). It is believed by some researchers that cool temperatures are needed for the plant to enter true-dormancy. Whatever the specific case, dormancy in many temperate woody plants develops more quickly when short days occur in combination with cool temperatures.
INFLUENCE OF WATER AND NUTRITION
Both water supply and mineral nutrition also interact with dormancy induction. Water stress will deepen dormancy and if severe enough will result in a resting bud and defoliation in some trees. High mineral nutrition can result in delaying dormancy. This is particularly true with the mineral nitrogen. High levels of nitrogen should never be given to plants in late summer or early fall since they may actually flush and resume growth. For the deepest dormancy, nurserymen will reduce day length, reduce temperatures, cut back on fertilization and mildly water stress plants.
RELEASE FROM DORMANCY
RELEASE FROM DORMANCY
Temperate woody plants once in true-dormancy require chilling to enter post-dormancy. Temperatures above freezing and in the range of 2° to 4° C are considered best. The amount of accumulated hours at these temperatures varies but is typically between 500 and 2,000 hours. Often species or seed sources form more northern climates require more hours but this is not a perfect rule. Fruit growers and nursery managers will often keep track of these so called chilling hours so they know when their trees have entered post-dormancy.
RELEASE FROM DORMANCY
Some researchers believe that during short days in the fall ABA builds up to high levels and induces dormancy. Chilling may be responsible for the breaking down of ABA. Until enough hours have accumulated to remove the inhibitory effect of ABA the plant will not break bud. At the same time when the soil begins to warm promoters of growth such as gibberellin and cytokinins build up signaling the bud to resume growth.
RELEASE FROM DORMANCY
Once adequate chilling has occurred and the plant is in a post-dormant condition, warm temperatures and increasing day lengths are required for normal shoot expansion. Warm temperatures are probably the most critical environmental factor at this point. Trees of the same species growing in the north will break bud later than the ones growing in the south. However, research has also shown that plants kept under warm temperatures but short day lengths broke bud later than plants kept in warm temperatures and long daylengths."
http://www.cnr.vt.edu/dendro/forestbiology/htmltext/chapter6.htm
So what does all this say? we need BOTH!
well..we knew that already.
well..it also says that photoperiod *triggers* dormancy..and cold temps *keep* dormancy..which makes sense..
all plants go into dormancy very slowly..over a period of 2 or 3 months..so you need that photoperiod to begin the process, then cold completes the cycle and the plant enters true dormancy..short photoperiod without following cold wont be true dormancy..(the indoor bonsai..they night have started to think about dormancy, but didnt get the conditions necessary to complete the job..)
and conversly, just instant cold without long preparation (photoperiod and coolere temps) also wouldnt work..(like instantly sticking your VFT into the fridge in July!
so..to KEEP and hold a true dormancy, once the process has begun, you need to maintain the cold temps..(bringing us back to mid 40's for the VFT!
to *trigger* dormancy in the first place, you need decreased photoperiod..(and cooler temps? probably..)
which bring us (well..me anyway) full circle..
give Cps a good natural cool crisp autumn, keep them outdoors straight through late October, so they naturally, slowly, go dormant..then..once its TOO cold for them outdoors (if you live in the north) bring them indoors, and KEEP them cold all winter!
(45 degrees average!
)
*whew*..
