Broad leaved , evergreen flora experience in the temperate realm of the man face quite a challenge come winter metre . freeze temperatures , want of water , and often intense sun can claim quite a toll on sustenance tissue paper . These are likely just some of the reasons why , comparatively speaking , extensive give evergreen plant are a rare happening in temperate zone . By far the most popular mathematical group of plant in this family are theRhododendrons .
Many a Rhodo buff has said that they can tell how cold it is outdoors by expect atRhododendronleaves . Indeed , as temperature drop , the leaves of these evergreen plant bush frequently droop and draw in up like green cigars . These folio movements do seem to be tie to the weather but their triggers and function have been the source of a lot of debate . Certainly not allRhododendrons are stale hardy but those that are seem to benefit from reorienting their parting . Why does this hap ?
In the past it has been suggested that leaf reorientation may have something to do with abridge snow load . If the leaves were to remain horizontal , this could cause enough snow buildup to break off branches . The fact that a considerable amount of icing and C. P. Snow can accumulate on branch regardless of leafage position , and largely without harm , seems to suggest that this is not the case . Others have suggest that it could be a way to reduce water loss . As the folio sag and curl , they are hypothetically increase the humidness around their leave and thus reducing their chance of desiccation .
This seems somewhat far fetched for a few reasons . For starters , Rhododendronsimply do not open their stomate during the colder months . By stay fresh them close , there is no net transferral of water into or out of the leaf . Also , their thick , waxy cuticle keeps water within the leaf from evaporating out as well . Finally , leaf loll and curling happens long before the ground freeze and therefore does n’t seem to be triggered by a lack of weewee in the surroundings .
The take theories on this phenomenon seem to deal more with military issue at the cellular grade . The first of these has to do with the sensitive photosynthetic machinery inside the chloroplasts . Leaf drooping may actually be a response to increase light . Though we generally do n’t think about photosynthesis in the winter calendar month , evergreen plant plant in reality experience the highest light intensity of the year during this sentence menses . Throughout the growing time of year , they are generally shadow by the overstory . However , once the canopy leaves decrease , thing alter .
Because the plant are , for the most part dormant , the photosystems within the chloroplasts have no way of dissipate the energy from the incoming sunlight . Photosystem II is especially vulnerable under such scenario . Experiments have render that foliage that were forced to stay horizontal during the winter experienced permanent sunshine damage and photosynthesized substantially less than leaves that were allow for to droop once favorable temperature returned . The thought is that by positioning the leaves vertically , the plants are reducing the amount of verbatim visible light hitting them throughout winter and therefore reducing the potential for promiscuous price .
These experimentation also let out something else about the changes in leaf position when it comes to Supreme Headquarters Allied Powers Europe . As it wrench out , curling made no difference of opinion in protect the leaves from clean damage . It would seem that drooping and curling are responses to two unlike types of environmental stress . So , why do the foliage curl ?
The solvent to this doubt is physical and one that has gained a mickle of inquiry attention in the field of cryogenics . When survive tissue freeze , ice crystal build up to the point that they can rupture cell membrane . This is only exacerbate if the tissues thaw out quickly . Anyone that has ever tried to freeze and then thaw leafy vegetables know what I am talking about .
To advantageously preserve tissues via freezing , they must freeze quickly , which reduces the size of the ice crystals that can take form , and then thaw out slowly . Researchers found thatRhododendronleaves immobilize completely at temperature below -8 degrees Celsius ( 17.6 degree Fahrenheit ) , temperatures that come on a regular basis throughout the range of temperate Rhodo species . Again , experiment were able to demo that flat leaf thaw much more rapidly than curled leaves . This is because a coil foliage exposes far less Earth’s surface area to the thaw sun than does a unconditional leaf . As such , curled leave do n’t thaw out as fast and thus are able to void much of the damaging effect of daily freeze - thawing cycles .
Though these are all components of the Rhodo foliage puzzle , there is still much work to be done . What we do fuck is that leaf droop and folio curling are two separate demeanor responding to unlike environmental pressures . Indeed , it appears that these two traits seem to be tied to cold hardiness in the genusRhododendron . What the exact triggers are and how they get the changes in shape and orientation , as well as the mechanics of winter survival at the cellular level are topics that are going to require further study . Until then , I call up it ’s dependable to say that we can appreciate and , to some degree , rely on the spot forecasting abilities of these wonderful shrub .
SOURCES :
Featured Photo : Hanna Sorensson , CC BY - SA 2.0,Flickr.com
“ Why Do Rhododendron Leaves Curl ? : A physiologic ecologist looks at the significance of temperature - sensitive folio trend in rhododendron , ” Erik Tallak Nilsen , Arnoldia , ( Arnold Arboretum , Harvard University , 1990 )
“ Seasonal and diurnal foliage front of Rhododendron maximum L. in counterpoint irradiance environments , ” Erik Tallak Nilsen , Oecologia65 , 296–302 ( 1985 ) .
“ Does Winter Leaf Curling Confer Cold Stress Tolerance in Rhododendron?”Journal of the American Rhododendron Society(E.T. Nilsen and A.Tolbert , Va. Tech )
