Let's Talk Stomata

[markyscott]

Recently I saw this info related to transpiration rate and water loss differences between juvenile growth and mature scale needles on junipers:

" ...The morphological differences between awl-shaped juvenile needles and scalelike adult needles in junipers is linked to a suite of physiological traits that favors establishment of juveniles and persistence of adults (Miller et al. 1995). Juvenile foliage requires less energy to produce, and its characteristics of high rates of CO2 assimilation and transpiration and lower investment of biomass and nitrogen per unit area enhance establishment and early growth. However, high rates of CO2 uptake and transpriation cause high rates of water loss, which are not sustainable for the adult tree in the dry native envionment of junipers of eastern and western North America. Therefore, the conservative use of water and nitrogen resources associated with adult scalelike foliage is a successful stress-tolerant strategy of the adult trees. (From Michigan Trees, A Guide to the Trees of the Great Lakes Region, Barnes and Wagner, 2004)

Have any of you found ornamental juniper cultivars that retain juvenile needle growth when older to have higher water needs?

Scott

 

[Poink88]

No answer to your question but the quoted article is great.

I've read the same and it went further to use the analogy of a car. Lower gear is equated to juvenile leaves...gives a starting boost to the tree (car) but is not efficient for sustained growth. Adult foliage is the equivalent of higher gear....not as powerful but much more efficient and suited for sustained growth (cruising speed). A slow down (repotting, major pruning, etc.) may trigger the plant to "shift down" to match the new condition.

Very interesting actually.

 

[edprocoat]

You say Stomata, I say Stomato.....

ed

 

[daygan]

Good quote. It is helpful to understand what exactly causes the tree to alter its foliage 'architecture'. Sorry, I can't give you any experiential input, but I do think that it may be, more often, that persistence of juvenile foliage in mature trees would be a result of receiving more water, and/or experiencing less environment-induced transpiration, such that there is less demand to transition to a tighter, more sustainable foliage architecture.

Of course, it also makes sense that there might be trees with genetic variation that inhibits transition to mature foliage, in which case they would need more water to counterbalance greater transpiration. I suppose you're looking for anecdotal evidence to support the claims.. There was a thread a few months ago about someone's juniper that had reverted to juvenile foliage where some similar concepts were discussed... let me see if I can find it...

 

[Vance Wood]

Good quote. It is helpful to understand what exactly causes the tree to alter its foliage 'architecture'. Sorry, I can't give you any experiential input, but I do think that it may be, more often, that persistence of juvenile foliage in mature trees would be a result of receiving more water, and/or experiencing less environment-induced transpiration, such that there is less demand to transition to a tighter, more sustainable foliage architecture.

Of course, it also makes sense that there might be trees with genetic variation that inhibits transition to mature foliage, in which case they would need more water to counterbalance greater transpiration. I suppose you're looking for anecdotal evidence to support the claims.. There was a thread a few months ago about someone's juniper that had reverted to juvenile foliage where some similar concepts were discussed... let me see if I can find it...

You have to remember that a lot of research on trees is only the appearance of cause and effect. We really don't know anything further than that and lacking any better indications we tend to look things like this as a fact. I am not saying it's not so, I am simply saying what I am saying.