Waterlogged Pereskiopsis (Personal & Literary observations)

hookahhead · March 17, 2014

Recently it has come to my attention that pereskiopsis seem to be the exception to the rule of limited water. The published research appears to confirm there is a significant difference in plant physiology between wet or dry conditions (See Post #11 of this thread).

Over the past 2 months I have kept these two containers very wet. Neither of the large rectangular containers have drain holes in the bottom, and at times I have had water just sitting in there. The plants seem to love it. I have one other setup like this that I forgot to take pictures of, but will tomorrow. Those plants are doing just fine as well.

However I know that this can lead to salt accumulation and anaerobic conditions so I redesigned a little. The white lid hopefully will reflect some of the light back onto the plants. The new tub has drain holes, and is elevated to allow better air flow between cells. The cups are plastic yogurt containers. The white powdery stuff is DE.

Edited May 7, 2014 by hookahhead

watertrade · March 17, 2014

I have for a long time have sworn that the best pereskiopsis are grown in a tropical wet. Which is probably consistent with their native climate. The only time I have had trouble is just as you say, when anaerobic environment develops. And when it's cold. But in the growing months, I keep them wet and let them dry to damp between waterings.

Edit : I also think the wet environment contributes to 'orange rot' fungi in grafted pereskiopsis, so care should be taken, And it probably would be a good idea to let them dry out every now and then too.

Edited March 17, 2014 by watertrade

hookahhead · March 17, 2014

That's certainly a good point about orange rot water trade. The scions would not fare well in humid conditions. However, the scions are a fair distance from the wet feet of the perskiopsis. Also it is winter for me since I am in the US, therefore my the air in my house is fairly dry. Airflow is another important thing to consider when inhibiting rot. The conditions inside my grow closet are no where near tropical and most of my pots are dry within 3-4 days.

Edited March 17, 2014 by hookahhead

Optimystic · March 17, 2014

I've been more often rooting my pereskies in cups with shallow water/nutes... i start them off with kelp water to root... the key is remove

the bottom leaves and remove any leaves that fall into the water.... so long as that is done they can root and swim for two months or

more.. they get too tall after a bit eh... once they get going they drink (what doesn't evaporate) up 1.5 inches of water in about 7-10 days,

so i check about once a week...they naturally dry themselves out when its warm enough... they retain more leaves when this method is done

in clear cups where light can pass through....

then i dry them out for a few hours to a day, stabilize them with packing peanuts, trim to fit in the dome, and graft to them while they're still in the cups! I just got done with all my runts and many little graft pups and well I was able to easily fit 50 grafts in a standard 1020 tray... (25cm by 50cm) which I think it pretty awesome especially with limited space to work with

Im glad to see that someone else uses the yogurt cups! those look more like pudding cups here but i've been using both though

i've weened myself off the pudding... I throw the tips i've trimmed into those pudding cups and they serve as backup stock.... and if

they don't get enough light they turn into grafting experiments, usually thinner sized stalks I use if I have tiny runts to graft

I really like that idea with the grafts... gave me an alternative to repotting all my older grafts while giving them more root space....

they're kinda top heavy tho... hopeully i'll be able to balance them out lol I think I can make it work in a large pot only filled 2/3 of the way...

I'll try it out with a few of the smaller grafts from the end of 2013 and see how things work out... many have roots already growing out

of the bottoms but since they're styro I can just rip the bottoms off and situate them in soil.... (BINGO)

I think for tricho scions, you really can't go wrong with humidity (perhaps bridgesii exception), at least here in Tejas where its damn near impossible to duplicate their "wet season" in the middle of our summers... definitely gonna be worth some experimenting here... when its hot here I intententioally overwater so theres some drizzle in the bottom of the tubs but its usually evaporates in a day... I also like the tubs so as to water them from the bottom up...

I don't know how I didn't think of something like that! lol spring is just starting here and since I don't have a tarp covered hoophouse

for now i've been fretting about how to manage with all these top heavy grafts in little cups LOL

with a tweak or two, this may just turn out to be my hot summer solution... I can't resist putting a few in the ground tho

Edited March 17, 2014 by Spine Collector

mutant · March 17, 2014

Pereskiopsis root in water! its supposed one of the first cacti

hookahhead · March 17, 2014

@Spine Collector, they do love the extra root space. A plant can only get as big as it's root system allows. I like this method because it allows me to pack them in close like using a seedling tray, but gives them way more room leg room. One thing you could do to help support them is add some fish tank or similar small gravel to the top 1/4 of the cup, to provide some stabilization. You could also do something like is used in MJ cultivation, a "screen of green"

http://www.sanniesshop.com/scrog-growing.html

Right now my potting mix is 1/4 coarse sand, 1/4 coco-coir, 1/4 perlite, 1/4 home worm castings by volume. However I would like to experiment with this idea using a media like crushed limestone, molar clay and other ingredients similar to soiless/mineral mixes for lophs. Then Ebb/Flow or maybe DWC hydroponic system. However, that is honestly to much for me to screw with at the moment. It is easier to just dump some water or casting tea in and be done.

Edited March 17, 2014 by hookahhead

hookahhead · April 24, 2014

So far these plants are doing great. Notice the nodes are tight and the leaves are are huge, thick, dark green and healthy looking. They look much better than most of mine that are in normal pots. I have been keeping things fairly wet. I typically add enough water to where I can actually seethe water level rising from the bottom of the container. Lately I have been watering every 2-3 days, as the soil has already dried a bit by then. Plants are cool. They absorb some lightwaves, suck up a bit of water, and presto-changeo a carbon dioxide molecule becomes a sugar. The sugar is rapidly converted to starch and stored as fuel for later. Of course it's a tad more complex for cacti.

hookahhead · April 28, 2014

Every person is unique, and therefore every garden is unique. As we spend time tending to them we learn what works best for each of us. So far this is working out nicely for my needs. It's compact, low maintenance, and I'm seeing some nice growth. :shroomer:

Here's the one I set up in the OP

This one has been going for a couple months now. The larger trichos were variously aged grafts that I transplanted from clay pots.

1-9-14

Today!

After all, necessity is the mother of all invention. :wink:

10-12-13

3-31-14

Edited April 28, 2014 by hookahhead

Philocacti · April 28, 2014

Great work man

hookahhead · April 29, 2014

Here is another one that has been chugging along for a bit (the one to the right is from the previous post). Of course for me, the biggest advantage of this method is everything is recycled/free. As you can see, you can pretty much make one of these out of whatever junk you can find.

1-6-14

Today!

Alright, I'm sure everyone already knows perskiopsis can handle a lot water, but the bottom of this one is looking a bit more like soup than soil :wacko:

Admittedly, this is an extreme case; I try to keep the soil damp, not exceesively saturated as this shows. I would definitely let this dry out a bit (2-4 days) before watering again. I have tried checking these with a generic moisture meter, but it doesn't seem to be very accurate.

Additional pictures of the grafts can be found in #396 of nitrogen's Connoisseur hybrids tread.

However, I wasn't aware dragon fruit are excellent swimmers too! (I removed them before taking the pictures above...didn't want to ruin the surprise.)

Clearly my indoor lighting isn't strong enough to keep them from stretching, and I have had a few get a little out of control. I honestly didn't want anymore of these, however I have a tough time killing/tossing a healthy plant... So I simply shoved them in here because they didn't take up any space that way. Out of sight, out of mind.

What the hell? These things were literally sitting in water a pool of water only a few minutes before the pictures. They have been in these conditions for at least 2 months now, but still no signs of rot. :scratchhead:

Don't take my word for it though, try it for yourself!

Edited May 7, 2014 by hookahhead

hookahhead · May 6, 2014

I'm sure you've all seen this equation before...

6CO₂ + 6H₂O C₆H₁₂O₆ + 6O₂

As you can see, it takes 6 CO₂ AND 6 H₂O molecules to yield a single sugar molecule.

Therefore, a plant must uptake significant amounts of each for vigorous/optimal growth.

Now this is kind of interesting...

Leaf and Stem CO₂ Uptake in the Three Subfamilies of the Cactaceae
Park S. Nobel and Terry L. Hartsock
Plant Physiology, Vol. 80, No. 4 (Apr., 1986), pp. 913-917

Net CO₂ uptake over 24-hour periods was examined for the leaves and for the stems of 11 species of cacti representing all three subfamilies. For Pereskia aculeata, Pereskia grandifolia, and Maihuenia poeppigii (subfamily Pereskioideae), all the net shoot CO₂ uptake was by the leaves and during the daytime. In contrast, for the leafless species Carnegiea gigantea, Ferocactus acanthodes, Coryphantha vivipara, and Mammillaria dioica (subfamily Cactoideae), all the shoot net CO₂ uptake was by the stems and at night. Similarly, for leafless Opuntia ficus-indica (subfamily Opuntioideae), all net CO₂ uptake occurred at night. For leafy members of the Opuntioideae (Pereskiopsis porteri, Quiabentia chacoensis, Austrocylindropuntia subulata), at least 88% of the shoot CO₂ uptake over 24 hours was by the leaves and some CO₂ uptake occurred at night. Leaves responded to the instantaneous level of photosynthetically active radiation (PAR) during the daytime, as occurs for C₃ plants, whereas nocturnal CO₂ uptake by stems of O. ficus-indica and F. acanthodes responded to the total daily PAR, as occurs for Crassulacean acid metabolism (CAM) plants. Thus, under the well-watered conditions employed, the Pereskioideae behaved as C₃ plants, the Cactoideae behaved as CAM plants, and the Opuntioideae exhibited characteristics of both pathways.

"Adult plants of each species were maintained in environmental chambers with day/night air temperatures of 25/15 C. A PAR of 800 umol m-2 s-1 on a horizontal surface and averaging 500 umol m-2 s-1(determined with a LiCor LI-190S quantum sensor) in the planes of the leaves or the stems considered was provided for 12 h each d (70%by Sylvania 60-W warm-white fluorescent lamps and 30% by Sylvania 300-W cool-beam tungsten lamps). The water vapor concentration was 10 g m-3 and the CO2 level was 350 ,ul/l by volume. Plants were routinely watered twice weekly with 1/20 Hoagland solution No.1(10) so that the soil water potential in the root zone was always above -0.5 MPa (measured with Wescor PT51-05 soil thermocouple psychrometers)."

I have uploaded the article to dropbox

Despite being nearly 30 years old, it still has some useful insights!

Pereskiopsis do not behave like "normal" cacti (CAM).
You may want to leave you light on a little longer.
Keep your leaves at all cost.
They immediately respond to light.
They like to be "well-watered"

Here's one a little more recent

. They even had several species of pereskiopsis in the study!

Photosynthetic Pathway Variation in Leafy Members of Two Subfamilies of the Cactaceae.pdf

Patterns of 24‐h CO₂ exchange and diel fluctuations in tissue acid concentrations were measured in leafy and leafless shoots of 10 species in the Pereskioideae and eight species in the Opuntioideae (Cactaceae). The species were selected to represent a range of phylogenetic histories. Leafy shoots of all species in the Pereskioideae exhibited C₃ patterns of gas exchange, and net CO₂ exchange of leafless stems in all but one species was negative during the day and night. Although nighttime CO₂ uptake was not observed in shoots or stems of any of the pereskioid taxa, tissue acidity increased at night to a small degree in leaves of six species and stems of five species, indicative of low levels of CAM‐cycling. In contrast, in leafy shoots of nearly all species in the Opuntioideae, CO₂ uptake occurred during the day and the night. Gas‐exchange rates were typically greater during the day. As is typical of CAM, nighttime maximal water use efficiency often greatly exceeded daytime values. Tissue malic acid concentrations increased overnight in leaves and stems of all eight opuntioid species. Examination of the data from a phylogenetic perspective illustrates evidence of low levels of CAM scattered among the primarily C₃ members of the more ancestral Pereskioideae. Furthermore, such consideration of the taxa in the more derived Opuntioideae (comparing the genera from most ancestral to most derived, that is,Austrocylindropuntia → Quiabentia → Pereskiopsis → Cylindropuntia) revealed that CAM became increasingly less important in the leaves of the various taxa, whereas this water‐conservative pathway of photosynthesis became increasingly more important in the stems. The results of this study indicate that members of the Pereskioideae should be restricted to moister habitats or must restrict the timing of growth to wet seasons, whereas the observed combinations of the C₃ and CAM pathways in the opuntioid taxa should prove beneficial in conserving water in the sporadically arid tropical and subtropical habitats of these plants.

"University of Kansas under the following environmental conditions: photosynthetic photon flux density (PPFD) of 500–700 mmol m-2 s-1 at shoot height during a 14-h photoperiod, 30/20 C day/night air temperatures, and 40%/ 55% day/night relative humidities (RH). Plants were watered only after the soil in their pots had thoroughly dried. A commercial greenhouse fertilizer was added to the water weekly. All plants were well established, growing vigorously, and often flowering when used for the measurements described below. Plants were always kept well watered during all measurements.

This is section from the results discusses pereskiopsis specifically...

"Patterns of net CO2 exchange for whole shoots (including leaves) and leafless stems of the four species of Pereskiopsis were similar, and thus, diel patterns of gas exchange for only Pereskiopsis diguetii are presented here (fig. 6). Maximal rates of net CO2 uptake of the leaves greatly exceeded those of the stems. Rates of daytime CO2 uptake in leafy shoots were higher than those measured at night (fig. 6), except similar amounts of CO2 uptake were observed day and night in Pereskiopsis porteri (table 5). In all species of Pereskiopsis, daytime rates declined precipitously at midday and then increased in the late afternoon. This midday decline was attributable primarily to a decrease in photosynthetic capacity in Pereskiopsis gatesii, reflected in an increase in tissue internal CO2 concentration, whereas in all other species of Pereskiopsis the midday decline in CO2 uptake was a function of limitations in photosynthetic capacity as well as decreases in stomatal conductance (data not shown). For stems of these species, maximal rates of net CO2 uptake were similar day and night or were higher during the day and were typically restricted to the latter half of either time period (fig. 6; table 5). Very low rates of net CO2 uptake were observed only at the start of the nighttime in P. porteri (table 5). The instantaneous WUE of the leafy shoots was much greater at night than during the day in P. diguetii and P. porteri; however, similar values were measured in Pereskiopsis aquosa and P. gatesii (table 5). Overnight increases in tissue acid concentrations were substantial in both leaves and stems of the four species of Pereskiopsis (table 6). The majority of the nocturnal increase in acid in both leaves and stems was not attributable to uptake of CO2 from the atmosphere but reflected internal recycling of CO2 instead (table 6). Degrees of this internal recycling ranged from 50% for the stems of P. aquosa to 100% for leaves of P. gatesii (table 6)."

Part of the discussion...

"All plants here were well watered. Presumably, daytime CO2 uptake is suppressed under drought stress (Nobel and Hartsock 1987). Thus, these plants benefit from relatively high CO2 uptake rates during the day at a considerable cost of water as a result of low WUE but then presumably continue to absorb CO2 at night, albeit at low rates, during dry periods. Relative amounts of water loss during nocturnal CO2 uptake were substantially lower than daytime values in most comparisons for these taxa. This combination of C3 and CAM should prove advantageous in the tropical and subtropical habitats of these species of Opuntioideae (Gibson and Nobel 1986; Barthlott and Hunt 1993)."

Which leads to this...

Drought-induced shifts In daily CO2 uptake patterns for leafy cacti.pdf

For cacti with persistent, relatively large leaves, most shoot CO2 uptake under well-watered conditions occurs by the leaves using the C3 pathway. For three species in the primitive subfamily Pereskioideae, droughts of 7 or 14 days decreased leaf daytime net CO2 uptake by an average of 49 and 88%, respectively; these species always had a net CO2 release at night by the leaves and both at night and during the day by the stems. For three leafy species in subfamily Opuntioideae, 7 and 14 days of drought reduced leaf daytime net CO2 uptake by 90 and 100%, respectively. Although drought reduced the total CO2 uptake over 24 h, the average percentage occurring at night by the leaves of these species increased from 5% under wet conditions to 71% after 7 days of drought to 99% after 14 days of drought. For two of the three species of Opuntioideae, 7 days of drought caused the small net CO2 uptake by the sterns to shift from the daytime to the nighttime, while for the third species drought caused a reduction of its stem nocturnal net CO2 uptake. Thus, shifts from predominantly daytime to predominantly nighttime net CO2 uptake can be induced by drought for the leaves and the stems of leafy cacti in subfamily Opuntioideae, indicating a high degree of biochemical versatility.

What about the dragon fruit? They like water too!

CO2 uptake by the cultivated hemiepiphytic cactus, Hylocereus undatus.pdf

The climate of the native tropical forest habitats of Hylocereus undatus, a hemiepiphytic cactus cultivated in 20 countries for its fruit, can help explain the response of its net CO2 uptake to environmental factors. Under wet conditions, about 85% of the total daily net CO2 uptake occurs at night via Crassulacean acid metabolism, leading to a high water-use efficiency. Total daily net CO2 uptake is reduced 57% by only 10 days of drought, possibly involving stomatal closure induced by abscisic acid produced in the roots, which typically occupy a small substrate volume. Total daily net CO2 uptake for H. undatus is maximal at day/night air temperatures of 30/20°C, optimal temperatures that are higher than those for desert cacti but representative of ambient temperatures in the tropics; its total daily net CO2 uptake becomes zero at day/night air temperatures of 42/32°C. Stem damage occurs at 45°C for H. undatus, whose photosynthetic cells show little acclimation to high temperatures compared with other cacti and are also sensitive to low temperatures, -1.5°C killing half of these cells. Consistent with its shaded habitat, total daily net CO uptake is appreciable at a total daily PPF of only 2 mol m-2 day-1 and
2 is maximal at 20 mol m-2 day-1, above which photoinhibition reduces net CO uptake. Net CO uptake 22 ability, which is highly correlated with stem nitrogen and chlorophyll contents, changes only gradually (halftimes of 2-3 months) as the concentration of applied N is changed. Doubling the atmospheric CO2 concentration raises the total daily net CO2 uptake of H. undatus by 34% under optimal conditions and by even larger percentages under adverse environmental conditions.

"When H. undatus that has been droughted for 10 days is rewatered, a significant increase in net CO2 uptake occurs in 1 day, the CO2 uptake ability is half restored in only 2 days, and full recovery occurs in 7 days (P S Nobel and E De la Barrera, unpublished observations). Thus this cactus can respond rapidly to rainfall events, which may be crucial for its growth in tropical regions with frequent rainfalls (Freiberg, 1997; L ̧ttge, 1997) as well as of importance in developing irrigation schedules when it is cultivated as a crop (Mizrahi & Nerd, 1999; Nerd et al., 2002). Similarly, the hydraulic conductivity of the roots (a direct measure of plant water uptake ability) of two epiphytic cacti, Epiphyllum phyllanthus and Rhipsalis baccifera, decreases during drought but increases to the values under wet conditions only 3 days after rewatering (North & Nobel, 1994)."

Stem water relations and net CO2 uptake for a hemiepiphytic cactus during short-term drought.pdf

Hylocereus undatus is widely distributed naturally and is currently cultivated in 19 countries for fruit. Because of its relatively thin stems, H . undatus was hypothesized to respond to drought more rapidly than other cacti. Stem water potential, water content and thickness were monitored during drought to provide easily measured parameters to be correlated with net CO 2 uptake ability, allowing the development of irrigation schedules to optimize water-use efficiency. H . undatus exhibited Crassulacean acid metabolism, as maximal stomatal opening and net CO 2 uptake occurred at night. Although the soil water potential decreased to − 4.2 MPa during 12 days without watering, the stem water status parameters remained near their values under wet conditions ( stem of − 0.67 MPa, water content of 90.8%, thickness of 4.48 mm). The drought was accompanied by a 63% decrease in the maximal water vapor conductance and a 57% decrease in the maximal net CO 2 uptake rate, but when the roots were excised for plants under wet conditions, neither parameter decreased appreciably over a comparable time period. Injection of 100 m M abscisic acid into attached stems and placing cut ends of detached stems in such a solution substantially reduced gas exchange 1 day later; at 2 days after injecting the hormone, the maximal water vapor conductance was similar to the minimal daytime values under wet conditions and the net CO 2 uptake rate was inhibited by 97%. Abscisic acid produced in the roots apparently leads to stomatal closure for this hemiepiphyte—whose roots can occur in very limited soil volumes—as soon as the water supply starts to deplete rather than after a large fraction of its stem water is transpired.

Got to keep them well fertilized too...

Nitrogen relations for net CO2 uptake by the cultivated hemiepiphytic cactus, Hylocereus undatus.pdf

The net CO2 uptake ability of a vine-like cactus native to shaded habitats, Hylocereus undatus, was hypothesized to adjust more rapidly to changes in the applied nitrogen concentration, which can have major impacts on fruiting, than the more massive cactus most widely cultivated for fruit, Opuntia ficus-indica. Specific objectives were to examine the effects of applied N on stem N concentrations and chlorophyll levels, which can affect net CO2 uptake ability and hence growth. After 9 weeks, the total daily net CO2 uptake for H. undatus was only 26% less for the relatively low N concentration of 0.32 mM than for 8 mM N (the N concentration in 0.5-strength Hoagland solution; all other nutrients were maintained at their concentration in 0.2-strength Hoagland solution), compared with 2 weeks for major changes for O. ficus-indica in response to changing applied N. Based on the maximal net CO2 uptake rates at night for the Crassulacean acid metabolism H. undatus, the half-time for the shift in response to seven different N concentrations applied for 22 weeks was 12–13 weeks; the half-time for the attainment of the highest net CO2 uptake rate of 10 μmol m−2 s−1 in response to subsequent application of 16 mM N for 11 weeks was 8–9 weeks. After 22 weeks, the stem N level in response to 0.16 mM N was 0.9% by dry mass and the chlorophyll content per unit stem area was 0.30 g m−2 compared with 2.5% and 0.63 g m−2 for 16 mM N. Subsequent application of 16 mM N for 11 weeks reversed the observable stem bleaching and raised the chlorophyll toward the highest levels. Both the chlorophyll content and the N level per unit stem area are highly correlated with the net CO2 uptake ability of H. undatus and either could help assess the physiological status of this cactus....

...In any case, maximal net CO2 uptake ability and, by extension, maximal growth of H. undatus required substantial N concentrations in the nutrient solution, such as 8 mM, as is also the case for 1-year-old seedlings of the cacti C. gigantea, Ferocactus acanthodes, and T. chilensis (Nobel, 1983) as well as for intensively managed crops (Moorby and Besford, 1983; Huett, 1996; Langhans and Tibbitts, 1997). The quantifiable responses of H. undatus to the N concentration in the nutrient solution underscore the importance of this element for its net CO2 uptake ability and general physiological status and allow prediction of the conditions maximizing its growth."

Additionally, here is some evidence that this behavior is widespread and common among several species.

https://dl.dropboxusercontent.com/u/57030275/Environmental%20regulation%20of%20carbon%20isotope%20composition%20and%20crassulacean%20acid%20metabolism%20in%20three%20plant%20communities%20along%20a%20water%20availability%20gradient.pdf

Environmental regulation of carbon isotope composition and crassulacean acid metabolism in three plant communities along a water availability gradient.

Expression of crassulacean acid metabolism (CAM) is characterized by extreme variability within and between taxa and its sensitivity to environmental variation. In this study, we determined seasonal fluctuations in CAM photosynthesis with measurements of nocturnal tissue acidification and carbon isotopie composition (δ¹³C) of bulk tissue and extracted sugars in three plant communities along a precipitation gradient (500, 700, and 1,000 mm year⁻¹) on the Yucatan Peninsula. We also related the degree of CAM to light habitat and relative abundance of species in the three sites. For all species, the greatest tissue acid accumulation occurred during the rainy season. In the 500 mm site, tissue acidification was greater for the species growing at 30% of daily total photon flux density (PFD) than species growing at 80% PFD. Whereas in the two wetter sites, the species growing at 80% total PFD had greater tissue acidification. All species had values of bulk tissue δ¹³ less negative than — 20‰, indicating strong CAM activity. The bulk tissue δ¹³C values in plants from the 500 mm site were 2‰ less negative than in plants from the wetter sites, and the only species growing in the three communities, Acanthocereus tetragonus (Cactaceae), showed a significant negative relationship between both bulk tissue and sugar δ¹³C values and annual rainfall, consistent with greater CO₂ assimilation through the CAM pathway with decreasing water availability. Overall, variation in the use of CAM photosynthesis was related to water and light availability and CAM appeared to be more ecologically important in the tropical dry forests than in the coastal dune....

...Our data demonstrate that carbon gain by CAM plants along this precipitation gradient was greatest in the wet season indicating that seasonal water limitation has the potential to reduce carbon gain by approximately 75% at the relatively dry costal dune site and by 50% in the wetter forest sites, when comparing tissue acidification in the dry season versus the wet season. In addition, at the driest site, plant growing at lower light had grater rates of carbon gain, whereas in the two wetter sites, plants growing in the higher light microhabitat had greater rates of carbon gain. These results highlight a shift in the interaction between light and water availability along this gradient, in which we observed that, when water availability increases, plants were able to increase their tissue acidification at higher PFD. In addition our C13 data showed greater proportional use of nocturnal CO2 uptake of the CAM species at the driest site (Fig 2.). Moreover, species importance values and the proportion of CAM species in the communities increased from the costal dune to the tropical dry forests, suggesting a more favorable balance of light and water availability for CAM performance in the wetter, forested communities.

Watering converts a CAM plant to daytime CO2 uptake.pdf

"THREE different photosynthetic options have been identified in plants1,2: (1) most plants have the reductive pentose phosphate or C3 pathway, where CO2 is incorporated into ribulose-1,5-diphosphate (RuDP) to yield two molecules of 3-phosphoglyceric acid, a three-carbon compound; (2) the C4 mode, where the first photosynthetic products are four-carbon dicarboxylic acids like oxaloacetate and malate formed following CO2 incorporation into phosphoenolpyruvate (PEP); and (3) crassulacean acid metabolism (CAM), found in many succulent plants growing in arid regions. In the last, stomatal opening and net CO2 uptake occur at night, CO2 being incorporated by way of PEP carboxylase into organic acids. The tissue acidity decreases as the organic acids are decarboxylated during the day, when the internally released CO2 is prevented from leaving by the closed stomata. The water vapour concentration difference between the tissue and ambient air is less at night, and thus the night-time stomatal opening of CAM plants leads to overall water conservation. For example, the water lost per CO2 fixed averages about sixfold higher for C4 plants and tenfold higher for C3 ones than for CAM plants in natural conditions. The net daily CO2 uptake by CAM plants is less than for C3 or C4 plants, so CAM plants tend to be relatively slow growing….

…When water is readily available, strictly adhering to the water-conserving CAM mode may no longer be beneficial to a CAM plant. At least some supplemental daytime stomatal opening and CO2 uptake would become advantageous. Indeed, many CAM plants show a net CO2 uptake during the day when not under water stress; such daytime CO2 uptake increased as water became more available for Bryophyllum daigremontianum, Agave americana, and Dudleya farinose. The shift to daytime photosynthesis was only partial, however, as in all cases the night-time stomatal opening and net CO2 influx characteristic of CAM plants still occurred. In different experiements, Osmond et al. showed that subjecting Kalanochoe daigremontiana to 9 weeks of drought caused the carbon isotope discrimination ratio to shift from a value close to that for C3 plants towards that expected if all CO2 uptake took place at night in CAM mode. For A. deserti, it seems that watering can cause an essentially complete switch from CAM to daytime photosynthesis (Fig. 1). Such switching did not lead to greater net daily photosynthesis for winter days, but greater photosynthetic productivity would be predicted for the longer day-light periods occurring at other times of the year. Thus, the ability to shift modes of photosynthesis when water is not a limiting factor could be a distinct advantage to this plant.

I'd love to hear your comments, concerns, and even criticisms of this research?

Photosynthetic Pathway Variation in Leafy Members of Two Subfamilies of the Cactaceae.pdf

Drought-induced shifts In daily CO2 uptake patterns for leafy cacti.pdf

CO2 uptake by the cultivated hemiepiphytic cactus, Hylocereus undatus.pdf

Stem water relations and net CO2 uptake for a hemiepiphytic cactus during short-term drought.pdf

Nitrogen relations for net CO2 uptake by the cultivated hemiepiphytic cactus, Hylocereus undatus.pdf

Watering converts a CAM plant to daytime CO2 uptake.pdf

Photosynthetic Pathway Variation in Leafy Members of Two Subfamilies of the Cactaceae.pdf

Drought-induced shifts In daily CO2 uptake patterns for leafy cacti.pdf

CO2 uptake by the cultivated hemiepiphytic cactus, Hylocereus undatus.pdf

Stem water relations and net CO2 uptake for a hemiepiphytic cactus during short-term drought.pdf

Nitrogen relations for net CO2 uptake by the cultivated hemiepiphytic cactus, Hylocereus undatus.pdf