I thought this was an interesting read.
http://www.intechopen.com/books/abiotic-stress-in-plants-mechanisms-and-adaptations/stomatal-responses-to-drought-stress-and-air-humidity
I’ve also been googling on this topic. I’m wondering, in particular, what happens when a xerophyte or other desert species is crossed with relatives that inhabit regions of continuously high humidity.
For example, Harkness (1977) cross the arid-growing Rosa persica with R. rugosa. “…the seedlings from that cross try to make leaves from the seedling stem at intervals of 3 or 4 mms, and their effort exhausts them before they are very high.” It is easy to blame this on unspecified “incompatible genes”, but that doesn’t explain the failure. It would be interesting to compare the number of stomata per cm. of the parents and the hybrids.
http://bulbnrose.x10.mx/Roses/breeding/Persica/PERSICA.HTML
Desert plants may open their stomata during the night to avoid excessive water loss. A species found on the seashore or in a swamp would probably have more stomata per unit area. Also, we should recall that water lost by transpiration can reduce the temperature of the leaves. Maybe this is useful, sometimes.
Most of what I’ve found regarding Roses deals with greenhouse varieties, rather than species. And what I’ve found about desert plants does not include roses, though one report mentions Prunus armeniaca of the Rosaceae.
High relative humidity (RH>85%) reduces the life of cut roses, compared with moderate RH (60%). The reduction ranges from 10-80%, according to variety.
Roses grown at high RH have more stomata on their leaves, though the increase (relative to moderate RH) differs among varieties.
Some of the differences in response to varying relative humidity are correlated with the concentration of abscisic acid in the leaves.
In some combinations, grafting can increase abscisic acid concentration in the leaves (e.g., Mandarina onto Apache).
Rose cultivars also differ in their ability to close their stomata at night, resulting in differences in nocturnal transpiration (e.g., Madelon has high nocturnal transpiration, Sonia has low.)
http://www.plant-dynamics.nl/UserFiles/File/pdf/roos.pdf
A side-line of research: patchy stomatal conductance.
Researchers found that under some conditions, patches of stomata may oscillate in synchrony. All the stomata in a region surrounded by veins will operate together, but separately from other parts of the leaf.
http://booksc.org/book/18279723
Finally, a study of xerophytes grown under arid conditions (no Rosa species were mentioned):
“Stomatal apertures of seventy-eight species of xerophytes grown under arid conditions were greater at night than during the day. Most stomata were closed during the day, and especially during the hottest period. Many stomata opened at night, especially in the presence of dew or mist. Nocturnal opening did not occur at low relative humidities.”
http://onlinelibrary.wiley.com/store/10.1111/j.1469-8137.1970.tb02438.x/asset/j.1469-8137.1970.tb02438.x.pdf;jsessionid=827F10DBCB9C38071899EF293CF6DD7D.f04t01?v=1&t=ib2d5ozj&s=b5ffe7be4fe36dce9ba5c88da668e501366dac83
Another study of xerophytes.
http://booksc.org/book/5970203
Given that stomata are only one part of a very complex system, and extrapolating from stomata to the whole plant, I wonder if anyone has yet developed a model for respiration, transpiration, osmosis, root permeability, photosynthesis, photorespiration etc.
That’s a tall order.
The item I mentioned about patchy stomatal conductance discussed the fact that some phenomena may fall between the usual methods of analysis. Specifically, calculations based microscopic observations of stomata were contradicted by calculations based on whole-leaf respiration. In other words, the stomata of a single leaf may not all open or close at the same time, under uniform conditions.
Differences in relative humidity lead to differences in the number of stomata per unit of area in the leaves of greenhouse roses. That’s phenotypic plasticity. But this sort of plasticity may not be universal among species that are adapted to different habitats. As Lechowicz observed, “Patterns of plasticity in functionally important traits among closely related species can be quite disparate. What appears to be adaptive plasticity for one species, may well be maladaptive or selectively neutral for another.”
http://www.bgu.ac.il/BIDR/events/plast/plast-abst.htm
So, what happens when related species that are adapted to widely different habitats are hybridized? If the normal plasticity of one parent is suppressed by the other, then an abnormal plasticity may result. That looks (to me) like what happened with the R. persica x R. rugosa hybrids. Unable to increase the number of stomata per leaf, the hybrids compensated by producing too many leaves, too quickly.