Do junipers really "drink" water through their foliage?

[Clicio]

they work well enough that we haven’t gone extinct yet.

Well said.
Yet.

 

[Gabler]

Well said.
Yet.

I’m told I have a dark sense of humor, but I’d rather appoach death laughing than crying.

 

[Baku1875]

Another thing is - there is no barrier stopping the water drops formed on needles during misting, from falling onto the soil in the pot. I bet the soil gets moist as well, so it is also a point of water intake. The soil can even get wet, depending of the actual duration of misting.

https://www.researchgate.net/figure/Juniper-daily-averaged-transpiration-and-soil-moisture-content-0-to-08-m-thtot_fig5_341910054

In this study, transpiration rates are compared to soil moisture content, in the bottom left chart, soil moisture peaks in late Spring, and transpiration is almost at zero. June to early autumn, transpiration skyrockets despite drier soil. So it seems that Junipers drink most of the water that they need from February to may and can transpire as much as they need to regulate temperature from May to autumn. Transpiration ZEROS out before soil moisture bottoms out, implying that the tree is one step ahead of drier conditions.

The study also mentions the group dynamics of juniper woodlands, and mature juniper trees taking advantage of shaded areas' moist soil with their horizontal roots.

Something tells me that juniper survival has nothing to do with foliage chugging water, rather, it has to do with foliage controlling water loss ahead of dry conditions and having forest group adaptations as well as root adaptations to survive drought.

 

[haidij]

The main effect of watering foliage is to reduce transpiration (the evaporation of water from leaves which accounts for up to 90% of trees' water usage). This means the tree doesn't require as much water via its roots in the first place. This is why you bag up or mist cuttings, which have no roots initially.

 

[leatherback]

The main effect of watering foliage is to reduce transpiration (the evaporation of water from leaves which accounts for up to 90% of trees' water usage). This means the tree doesn't require as much water via its roots in the first place. This is why you bag up or mist cuttings, which have no roots initially.

I would be curious to know what this conclusion is based on. It is not what I concluded after a deep dive into literature a few months back.

 

[leatherback]

Some more reading @Clicio

Experimental cloud immersion and foliar water uptake in saplings of Abies fraseri and Picea rubens - Trees

Key message Frequent cloud immersion events result in direct uptake of cloud water and improve plant water potentials during daylight hours in saplings of two dominant cloud forest species. Abstract In ecosystems with frequent cloud immersion, the influence on plant water balance can be...

link.springer.com

In ecosystems with frequent cloud immersion, the influence on plant water balance can be important. While cloud immersion can reduce plant water loss via transpiration, recent advances in methodology have suggested that many species also absorb water directly into leaves (foliar water uptake). The current study examines foliar water uptake and its influence on daily plant water balance in tree species of the endangered spruce–fir forest of the southern Appalachian Mountains, USA. These mountain-top communities are considered relic, boreal forests that may have persisted because of the benefits of frequent cloud immersion. We examined changes in needle water content, xylem water potentials, and stable isotope values in saplings of the two dominant tree species, Abies fraseri and Picea rubens before and after a 24 h period of experimental cloud immersion. Both species exhibited foliar water uptake following immersion, evidenced by substantial changes in stable isotope values of extracted needle water that reflected the composition of the fog water. In addition, total needle water content improved 3.7–6.4 % following experimental submersion and xylem water potentials were significantly greater (up to 0.33 MPa) in cloud-immersed plants over control plants. These results indicate that foliar water uptake may be an adaptive strategy for utilizing cloud water and improving overall tree vigor in these most southerly distributed boreal species.

Redirecting

doi.org

Foliar water uptake (FWU) is the main mechanism used by herbaceous plants in arid areas to absorb small amounts of precipitation. It has an important ecological and hydrological effect for alleviating plant drought stress. However, it is unknown whether woody plants can absorb water through the leaves when water absorption via roots is insufficient. This study explored whether FWU exists and the FWU conditions in semi-humid rock mountainous areas. Isotopes were labeled to detect FWU under different soil water content (SWC) gradients (3.9–6.5%, 6.5–9.1%, 9.1–15.6%, 15.6–20.8%, and 20.8–26.0%) and different precipitation gradients (1 mm/h, 5 mm/h, 10 mm/h, and 15 mm/h) in simulated precipitation experiments with indoor potted plants. The results showed that FWU occurred in each treatment if the SWC ≤ 21.9% no matter the precipitation amount. Water absorption via FWU increased with the increase of precipitation intensity but decreased with the increase of SWC. The greatest ratios of FWU were 2.77% and 9.52% of precipitation intensity of 1 mm/h and 15 mm/h, respectively, in the 3.9–6.5% treatment. The precipitation absorbed by the leaves can be transported to the xylem or root system along the water potential gradient of leaves–branches–roots. The precipitation with reverse migration in branches and roots increased with the increase of the water potential gradient of leaves–branches–roots. These findings suggest that Platycladus orientalis can uptake water through roots and leaves, effectively alleviating drought stress. This study provides new insights into water use patterns and water migration in trees.

https://doi.org/10.1002/eco.2240

Fog, dew and cloud-borne mist are sources of water to vegetation in many ecosystems. The importance of fog as a water source has been documented well beyond ecosystems where plants experience fog for extensive periods over the course of the day (e.g. cloud forests); however, relatively little is known regarding the roles of fog and foliar water uptake in ecosystems such as coastal freshwater wetlands that do not experience fog for extensive periods over the course of the day. Coastal freshwater wetland ecosystems lie on the forefront of climate change-associated stressors that threaten freshwater supplies to vegetation. Considering the potential impact of climate warming on diminishing coastal fog regimes, an improved understanding of the ecophysiological benefits of fog immersion to the vegetation in these ecosystems is critical for understanding the response of these ecosystems to global climate change. Herein, we investigate the potential for foliar water deposition from fog to act as a direct freshwater subsidy to four tree species (Taxodium distichum (L.) Rich., Nyssa aquatica L., Nyssa biflora Walter and Liquidambar styraciflua L.) that are common in coastal freshwater wetlands. All four species showed the capacity for foliar water uptake across the leaf/needle surface, with a ca. 5–10% increase in leaf water content after a 3-h submersion experiment. Stable isotopes of water provided strong evidence for foliar water uptake in all four species and for bark water uptake in T. distichum after a 24-h fogging experiment. Fog exposure also resulted in several ecophysiological benefits to the saplings, including significant improvements in pre-dawn water status and net photosynthesis.

 

[Clicio]

Some more reading @Clicio

Experimental cloud immersion and foliar water uptake in saplings of Abies fraseri and Picea rubens - Trees

Key message Frequent cloud immersion events result in direct uptake of cloud water and improve plant water potentials during daylight hours in saplings of two dominant cloud forest species. Abstract In ecosystems with frequent cloud immersion, the influence on plant water balance can be...

link.springer.com

In ecosystems with frequent cloud immersion, the influence on plant water balance can be important. While cloud immersion can reduce plant water loss via transpiration, recent advances in methodology have suggested that many species also absorb water directly into leaves (foliar water uptake). The current study examines foliar water uptake and its influence on daily plant water balance in tree species of the endangered spruce–fir forest of the southern Appalachian Mountains, USA. These mountain-top communities are considered relic, boreal forests that may have persisted because of the benefits of frequent cloud immersion. We examined changes in needle water content, xylem water potentials, and stable isotope values in saplings of the two dominant tree species, Abies fraseri and Picea rubens before and after a 24 h period of experimental cloud immersion. Both species exhibited foliar water uptake following immersion, evidenced by substantial changes in stable isotope values of extracted needle water that reflected the composition of the fog water. In addition, total needle water content improved 3.7–6.4 % following experimental submersion and xylem water potentials were significantly greater (up to 0.33 MPa) in cloud-immersed plants over control plants. These results indicate that foliar water uptake may be an adaptive strategy for utilizing cloud water and improving overall tree vigor in these most southerly distributed boreal species.

Redirecting

doi.org

Foliar water uptake (FWU) is the main mechanism used by herbaceous plants in arid areas to absorb small amounts of precipitation. It has an important ecological and hydrological effect for alleviating plant drought stress. However, it is unknown whether woody plants can absorb water through the leaves when water absorption via roots is insufficient. This study explored whether FWU exists and the FWU conditions in semi-humid rock mountainous areas. Isotopes were labeled to detect FWU under different soil water content (SWC) gradients (3.9–6.5%, 6.5–9.1%, 9.1–15.6%, 15.6–20.8%, and 20.8–26.0%) and different precipitation gradients (1 mm/h, 5 mm/h, 10 mm/h, and 15 mm/h) in simulated precipitation experiments with indoor potted plants. The results showed that FWU occurred in each treatment if the SWC ≤ 21.9% no matter the precipitation amount. Water absorption via FWU increased with the increase of precipitation intensity but decreased with the increase of SWC. The greatest ratios of FWU were 2.77% and 9.52% of precipitation intensity of 1 mm/h and 15 mm/h, respectively, in the 3.9–6.5% treatment. The precipitation absorbed by the leaves can be transported to the xylem or root system along the water potential gradient of leaves–branches–roots. The precipitation with reverse migration in branches and roots increased with the increase of the water potential gradient of leaves–branches–roots. These findings suggest that Platycladus orientalis can uptake water through roots and leaves, effectively alleviating drought stress. This study provides new insights into water use patterns and water migration in trees.

https://doi.org/10.1002/eco.2240

Fog, dew and cloud-borne mist are sources of water to vegetation in many ecosystems. The importance of fog as a water source has been documented well beyond ecosystems where plants experience fog for extensive periods over the course of the day (e.g. cloud forests); however, relatively little is known regarding the roles of fog and foliar water uptake in ecosystems such as coastal freshwater wetlands that do not experience fog for extensive periods over the course of the day. Coastal freshwater wetland ecosystems lie on the forefront of climate change-associated stressors that threaten freshwater supplies to vegetation. Considering the potential impact of climate warming on diminishing coastal fog regimes, an improved understanding of the ecophysiological benefits of fog immersion to the vegetation in these ecosystems is critical for understanding the response of these ecosystems to global climate change. Herein, we investigate the potential for foliar water deposition from fog to act as a direct freshwater subsidy to four tree species (Taxodium distichum (L.) Rich., Nyssa aquatica L., Nyssa biflora Walter and Liquidambar styraciflua L.) that are common in coastal freshwater wetlands. All four species showed the capacity for foliar water uptake across the leaf/needle surface, with a ca. 5–10% increase in leaf water content after a 3-h submersion experiment. Stable isotopes of water provided strong evidence for foliar water uptake in all four species and for bark water uptake in T. distichum after a 24-h fogging experiment. Fog exposure also resulted in several ecophysiological benefits to the saplings, including significant improvements in pre-dawn water status and net photosynthesis.

Absolutely sensational @leatherback , thanks for posting!

 

[Bonsai Nut]

I've collected yamadori junipers with next to zero roots and with regular foliage misting they survive and grow new roots.

Just backing up what PaulH said. It is considered best practice when collecting junipers to only mist the foliage - and only at night when the stomata are open. They close their stomata during the day to reduce moisture loss. You want to avoid overwatering the soil because a newly collected tree will have minimal/stressed roots, and it is easy to make the mistake of keeping the soil too wet - and rotting new roots before the roots can establish themselves.

I believe this is also considered the best way to start juniper cuttings.

 

[Clicio]

Just backing up what PaulH said. It is considered best practice when collecting junipers to only mist the foliage - and only at night when the stomata are open.

I have been avoiding misting at night because I'm afraid of fungal issues, @Bonsai Nut . Wet foliage is prone to fungi, right? Am I being too cautious?

I believe this is also considered the best way to start juniper cuttings.

That's interesting! I'll surely try it out!

 

[Bonsai Nut]

I have been avoiding misting at night because I'm afraid of fungal issues, @Bonsai Nut . Wet foliage is prone to fungi, right? Am I being too cautious?

That's interesting! I'll surely try it out!

Typically in California the humidity is so low you don't have fungal problems except during wet cool winter weather. But it can happen.

I suppose if you don't mist during the day, it allows the foliage to dry during the day, which reduces the risk. Plus you could always treat for fungus prophylactically.

 

[PowerTap]

Another thing is - there is no barrier stopping the water drops formed on needles during misting, from falling onto the soil in the pot. I bet the soil gets moist as well, so it is also a point of water intake. The soil can even get wet, depending of the actual duration of misting.

It turns out that most plants get watered when it rains, and it rains on the foliage, where the tree takes a drink, then runs to the ground, where the tree takes a drink. If a tree doesn't gather water at the foliage, it's dependent on not being crowded out by other ground plants with their own root systems.

 

[Baku1875]

Just backing up what PaulH said. It is considered best practice when collecting junipers to only mist the foliage - and only at night when the stomata are open. They close their stomata during the day to reduce moisture loss. You want to avoid overwatering the soil because a newly collected tree will have minimal/stressed roots, and it is easy to make the mistake of keeping the soil too wet - and rotting new roots before the roots can establish themselves.

I believe this is also considered the best way to start juniper cuttings.

I thought the stomata open in the day (photosynthesis needs Co2) and close at night....

But after an interesting read, I learn that this is not always the case!

Night‐time conductance in C3 and C4 species: do plants lose water at night?

Abstract. Significant night‐time stomatal conductance and transpiration were found for 11 out of 17 species with a range of life histories (herbaceous annual, p

academic.oup.com

"It is generally accepted that for C3 and C4 plants stomatal closure minimizes transpirational water loss (E) at night when there is no opportunity for carbon gain. However, there is increasing evidence that some species maintain substantial stomatal conductance (g) and E at night. Arabidopsis, Betula, Brassica, Chrysothamnus, Fraxinus, Picea, Rosa, Sarcobatus, and Tilia all have substantial night‐time g, based on gas exchange measurements"

G and E are stomatal conductance and transpirational water loss.

There is also a caveat
"The lack of significant night‐time g and E in pinyon‐juniper woodland species was associated with very low daytime rates and may have reflected late‐season water stress in these conifers."

so water stress led to CLOSED stomata at night, BUT in a bonsai garden habitat with sufficient water, and during open stomata/high photosynthetic periods of transpiration day activity for Junipers (May-September), a case can be made for misting to protect against night time transpiration(which could ultimately damage foliar mass and ruin the plant's chances), especially for recently styled or repotted plants.

Otherwise, the juniper's excellent protective measures against water loss kick in and it locks down the stomata.

Then looking at the final list and 'verdicts', night-time g and E as a No meaning that it will not open stomata at night to a greater degree than daytime opening.

So compared to other plants in the study, Junipers are fairly 'stomata retentive' lol...

Species

Habitat

Photosynthetic pathway

Life history

Night‐time g and E

Juniperus osteosperma	Pinyon‐juniper woodland	C3	Tree	No
Pinus monophylla	Pinyon‐juniper woodland	C3	Tree	No

TLDR- night time misting is likely to be scientifically on point as a protective practice for collected or compromised junipers during high transpiration months as it does not compromise or slow day time photosynthesis, while protecting against night time water loss and leaf damage. That is basically the 'case against misting', it prevents Co2 from getting in and reduces photosynthetic rates, but if it adds a protective benefit at night...win/win situation.

 

[nuttiest]

HAHA I just sprayed the whole backyard down because of this thread - so junipers are sure to have a night drink. My junipers have been looking so scruffy in this months-long drought.

 

[n8]

Here is the photo from the day I got it.

You have the best pictures, amigo.

My only input is anecdotal: Like Paul, I have collected a few junipers with very few roots, pried out of a crack in the granite. The key to keep them alive those first two years is mist.

 

[caffeinated]

Generally, the stomata open during the day for transpiration and gaseous exchange. They need to be able to take in the CO2 for photosynthisis to happen and the transpiration helps to cool the plant. They close at night.


What triggers stomata to open?

Stomata open in response to blue light to facilitate gas exchange between the plant and the atmosphere. This response is key to terrestrial plant life, as gas exchange is necessary not only for photosynthesis but also for water uptake from the roots.

Blue Light Regulation of Stomatal Opening and the Plasma Membrane H+-ATPase

Recent progress of the blue light signaling pathway in guard cells highlights its regulation of H[+] -ATPase activity.

www.ncbi.nlm.nih.gov

Stoma - Wikipedia

en.wikipedia.org

 

[haidij]

I would be curious to know what this conclusion is based on. It is not what I concluded after a deep dive into literature a few months back.

Most text books talk about transpiration as a key process for trees (and the one which causes by far the most water use) but here are some good ones I have used:

• Vogel, S. (2012) The Life of a Leaf. Chicago, USA: The University of Chicago Press
• Ennos, R. (2016) Trees: A complete guide to their biology and structure. London, UK: Natural History Museum
• Thomas, Peter A. (2014) Trees: Their Natural History. Cambridge, UK: Cambridge University Press

I also reference this on my website with links to source articles:

The water system of a tree

One of the first topics you come across when starting to study trees is the question of how they manage to lift water all the way to the leaves at the top of th

bonsai-science.com

Watering bonsai trees

They say that a lack of watering is the number one reason that newbies kill their bonsai trees. It is quite a surprise when you first learn about the hobby to f

bonsai-science.com

Foliar Feeding

Some products advise spraying them on the leaves of your trees - a process known as foliar feeding. At first glance this makes no sense, as plants synthesise ev

bonsai-science.com

Attached are a couple of pages from Thomas talking about transpiration. There are different estimates depending on the tree and where you look but transpiration is supposed to comprise 80-95% of total water use by trees. So minimising this by increasing humidity at the leaf surface will have a major effect on total water use.

 

[Clicio]

Most text books talk about transpiration as a key process for trees (and the one which causes by far the most water use) but here are some good ones I have used:

• Vogel, S. (2012) The Life of a Leaf. Chicago, USA: The University of Chicago Press
• Ennos, R. (2016) Trees: A complete guide to their biology and structure. London, UK: Natural History Museum
• Thomas, Peter A. (2014) Trees: Their Natural History. Cambridge, UK: Cambridge University Press

I also reference this on my website with links to source articles:

The water system of a tree

One of the first topics you come across when starting to study trees is the question of how they manage to lift water all the way to the leaves at the top of th

bonsai-science.com

Watering bonsai trees

They say that a lack of watering is the number one reason that newbies kill their bonsai trees. It is quite a surprise when you first learn about the hobby to f

bonsai-science.com

Foliar Feeding

Some products advise spraying them on the leaves of your trees - a process known as foliar feeding. At first glance this makes no sense, as plants synthesise ev

bonsai-science.com

Attached are a couple of pages from Thomas talking about transpiration. There are different estimates depending on the tree and where you look but transpiration is supposed to comprise 80-95% of total water use by trees. So minimising this by increasing humidity at the leaf surface will have a major effect on total water use.

Thank you, @haidij .
Very interesting articles, glad you posted them.

 

[leatherback]

Foliar Feeding

Some products advise spraying them on the leaves of your trees - a process known as foliar feeding. At first glance this makes no sense, as plants synthesise ev

bonsai-science.com

Attached are a couple of pages from Thomas talking about transpiration. There are different estimates depending on the tree and where you look but transpiration is supposed to comprise 80-95% of total water use by trees. So minimising this by increasing humidity at the leaf surface will have a major effect on total water use.

But this does not state that the main effetc of wetting will be reduction of transpiration. The OP asked about water uptake by the tree through means otgher than the roots.

 

[Baku1875]

But this does not state that the main effetc of wetting will be reduction of transpiration. The OP asked about water uptake by the tree through means otgher than the roots.

A lot of the assumptions of stomatal mechanisms are being turned on their heads in the past 10 years. The study I ran across last night in my prior post indicated that the generalization that stomata simply 'close at night' is wrong, and that certain species will actively regulate stomatal opening based on root water availability, active growth status, and leaf humidity in TANDEM!

I just skimmed through this other study just now, and there's a lot of nuggets in here, one of the keys being ABA, abscisic acid, actively being able to control stomatal closure and that it can be rapidly synthesized IN the leaf tissue, and its bioavailability can also be modulated by drought conditions in the soil changing the pH of sap flow.

"Several recent reports have overcome this challenge, by
showing that abscisic acid (ABA), which is known to close stomata
by inducing solute loss from guard cells, is rapidly synthesized de
novo within leaves in response to reduced air humidity (Xie et al.,
2006; Bauer et al., 2013; McAdam et al., 2016b)."
Wilkinson & Davies (1997)
showed that xylem sap pH increased during drought, and that
increased sap pH caused stomatal closure regardless of drought –
perhaps by helping to sequester leaf ABA in the apoplast due to its
behavior as a weak acid. "

Page 12 This part supports moisture intake through stomata.....
Stomatal sensitivity to
ABA is modulated by changes in humidity experienced during
growth (Pantin et al., 2013b). Increased leaf osmotic pressure can
sustain stomatal opening during soil drought [presumably to allow ambient humidity INTAKE] (Turner et al., 1978),
and conversely, reduced hydraulic conductance at low water
potentials can enhance stomatal closure during drought

There is a hydropassive and hydroactive response.

Soil drought alters sap pH which increases stomatal sensitivity to ABA leading to closure to further preserve water and prevent transpiration, which goes AGAINST the passive response of stomatal opening in higher humidity.

This override implies plant ability to 'calculate' an appropriate stomatal opening based on ambient humidity, soil moisture, and growth status. The study from Ucdavis also states that ABA dynamics and stomatal responses differ greatly between seedless, angiosperm and gymnosperms (conifers).

https://buckleylab.ucdavis.edu/wp-content/uploads/sites/511/2021/09/buckley-2019-stomata-water-tansley-1.pdf

This is the next study that I want to take a look at, because it actually highlights gymnosperm stomatal mechanisms relative to ABA

Grantz DA, Linscheid BS, Grulke NE. 2019. Differential responses of stomatal
kinetics and steady state conductance to abscisic acid in a fern: comparison with a
gymnosperm and an angiosperm. New Phytologist 222, 1883–1892.

 

[haidij]

But this does not state that the main effetc of wetting will be reduction of transpiration. The OP asked about water uptake by the tree through means otgher than the roots.

Vogel's 'Life of a Leaf' has an in-depth explanation of transpiration and water loss through leaves which I'd recommend for lots of detail (chapter 5 'Leaking Water').

In this, he says" For some plants, 97 percent of the water they absorb—almost entirely as liquid entering their roots—just . . . well, it just disappears into thin air, almost all through their leaves. Rather than diffusing in through the stomata as does CO2, water vapor diffuses out, often in prodigious amounts. Trees manage to suck the stuff out of the soil, even out of fairly dry soil, and they then lift it up to their leaves. Then they simply allow almost all that water to evaporate out into the atmosphere. We’re talking about big-time hydraulic heroics: a large tree may lift as much as 110 gallons, or 500 liters, every day." And later he also says that "only if the relative humidity is 100 percent will water not be lost."