Lodgepole Pine Repot Experiment

0soyoung

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I have just potted 16 lodgpole pines (P. contorta var. latifolia) seedlings, to start my repotting-plus experiment (pretty much as I described in the “Let’s All Get Some Answers and Not Wait for the Book” thread):

treerepotrhizocutsshoot prudefol
1---++
2+----
3-+--+
4++-+-
5--++-
6+-+-+
7-++--
8+++++
9----+
10+--+-
11-+-++
12++---
13--+--
14+-+++
15-+++-
16+++-+

o repot ‘+‘ = Aug/Sep
o repot ‘-‘ = spring
o rhizo ‘+‘ = nested clear orchid pot & proLeague
o rhizo ‘-‘ = MVP in black pot
o cuts ‘+’ = cuts at stem base done at repotting
o cuts ‘-‘ = do nothing
o shoot pru ‘+’ = nip shoot tip to just remove terminal leaves
o shoot pru ‘-‘ = do nothing
o defoliate ‘+’ = remove fraction of leaves by cutting through petiole
o defoliate ‘-‘ = do nothing

I decided that I will try to measure root growth, in addition to monitoring the ‘above ground’ growth. To facilitate measuring root growth, I am using 6 inch clear orchid pots (filled with dark colored Turface proLeague Heritage Red to contrast with growing roots) as a new experiment factor, ‘rhizo’. These ‘rhizotrons’ are nested within a gallon size black plastic pot. I will periodically remove them to estimate the root growth. The other trees (not in clear orchid pots) are potted in one gallon black plastic pots filled with Turface MVP.

I cut off the ‘needles’ from one side of the central leader of those trees getting the defoliation treatment. The idea is to see if back budding preferentially occurs where needles are (ala mugo pines) or where they are not (ala JBP). I left any existing buds untouched.

Lastly, I gave each 1 teaspoon of Osmocote 14-14-14.

tree idbase dia (mm)defolcutswt (gm)clr pot
13.45yesno4no
24.93nono11no
36.55yesno24yes
48.65nono43yes
55noyes13no
64.09yesno6no
75.68noyes16yes
84.2yesno15yes
93.37yesno21no
106.01nono38no
115.46yesno11yes
125.06nono14yes
135.6noyes14no
145.75yesno16no
154.28noyes16yes
165.9yesno14yes
 

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amkhalid

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Did you try to control for genetic variation in any way? i.e. what is the seed source?
 

amkhalid

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No. Arborday.org had a deal. The certify that they are 1 to 2 yr var. latifolia seedlings but nothing further about the seed provenance.

Then keep in mind this variable will always limit the conclusions you can make, no matter what the result of this experiment. The "goal" of sexual reproduction is to produce as much genetic variation as possible. So seeds are tricky to use for controlled experiments. Ideally the seeds would come from a highly inbred lineage or hopefully at least resulted from the self-pollination of a single parent.
 

amkhalid

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If we change "will always" to "may" or "might", I would agree.

Well lets say you spend x amount of time doing this experiment, get an interesting result, and come back to present it to us. There will be people asking "how do you know your result isn't just due to the natural variation between the seedlings?" Your response will have to be "Well... I don't".

I appreciate that you are trying to be scientific with your horticulture, but I'm just trying to help your experimental design so you don't waste your time.

Since controlling for the genetics is difficult, you could take the approach of repetition. It seems you have 16 different experimental conditions. Why not do just 4 experimental conditions, each repeated 4x? Then if all 4 repetitions show the same result you will have some convincing evidence, regardless of the genetics.

Even if you controlled for the genetics, you still need repetition to show that your result is reproducible, and not a fluke.
 

0soyoung

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Well lets say you spend x amount of time doing this experiment, get an interesting result, and come back to present it to us. There will be people asking "how do you know your result isn't just due to the natural variation between the seedlings?" Your response will have to be "Well... I don't".

I appreciate that you are trying to be scientific with your horticulture, but I'm just trying to help your experimental design so you don't waste your time.

Since controlling for the genetics is difficult, you could take the approach of repetition. It seems you have 16 different experimental conditions. Why not do just 4 experimental conditions, each repeated 4x? Then if all 4 repetitions show the same result you will have some convincing evidence, regardless of the genetics.

Even if you controlled for the genetics, you still need repetition to show that your result is reproducible, and not a fluke.

Thanks for your comments. I appreciate the discussion.

Lets just for a moment consider answering the basic question of whether repotting time has a significant effect. There are 8 seedlings that will be repotted Aug/Sep and another 8 that will be repotted in the spring. I will compare the average seasonal weight increase of the 8 spring repotted trees to the average seasonal weight increase 8 repotted in Aug/Sep (there are 8 trees in each group '+' and '-' of every factor).

The variation in seasonal weight gains in both groups determines whether my experiment can resolve whatever effect there is in this regard. I don't have any way of knowing this variability a priori, so I've made a decision based on a rule of thumb and on practical factors (e.g., affordability, space for growing, etc.).

At any rate, one represents each group of 8 trees by a t-distribution. The statistical hypothesis of all experiments is that there is no effect. If these two distributions overlap significantly, one concludes that the hypothesis is not refuted by the data. One can then choose to say 'Good enough, there is no effect for the level of scrutiny I am interested in.' or decide to repeat the experiment with more trees (and one would then have some idea of how many trees will be needed to possibly resolve whether there is any effect).

I previously 'discussed' the experiment resolution given the possibility that the response to repotting time is that trees die.

Finally, I guess it is worth repeating that even though I have my reasons for this experiment, I have the ancillary aim that BNuts will repot some trees in the spring and repot some others in Aug/Sep and share their data. Then we collectively would have some indications the possible significance of factors such as climate, geographic location, genetic variations, and etc., including accomplishing replication of the test.
 

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amkhalid

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I guess I'm still not sure what your question is. If you are just trying to determine best time to repot, I would probably design a much simpler experiment with only two or three groups, leaving out variables like pruning, myco, etc.

And wow - if your distribution ends up looking like that... talk about textbook results :)

Keep us posted. Thanks for the discussion. I shouldn't be thinking this much in a bonsai forum :)
 

0soyoung

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I guess I'm still not sure what your question is. If you are just trying to determine best time to repot, I would probably design a much simpler experiment with only two or three groups, leaving out variables like pruning, myco, etc.

And wow - if your distribution ends up looking like that... talk about textbook results :)

Keep us posted. Thanks for the discussion. I shouldn't be thinking this much in a bonsai forum :)

The link at the start of this thread will take you to the background. The basic question was whether mugo pine is the only specie that can be or benefits from repotting in Aug/Sep instead of spring. My theme has been that there is no need for this taking 10-plus years to figure out - if Vance Woods had just had a few friends that would do similar experiments, it could be known in far less time and for places in the world other than just Vance's.

I think it is fairly intuitive to compare two groups, a control and a treated group. Maybe I should have just left it at that and not make people regret they started to read my threads. But, there are issues like 'how do you treat it?' and 'why don't we have a book?' that keep coming up, so I decided to ... do what I've done. FWIW, this is a fractional factorial design.

The illustration is just an illustration of concept. :cool:

BTW, I enjoy reading your blog.
 
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0soyoung

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Progress - initial potting effects

At this point 4 6 of my 16 lodge pole pine seedlings have died: #2, #9, #10, and #14 plus #4 and #13. Partial defoliation, potting, and cuts are the only experiment treatments that have been applied. I decandled the 'shoot pru' = '+' seedlings on 18 May (the same time as I decandle black pines).

It appears that my seedlings were weak when I received them and that potting in shallow containers filled with fine grained Pro League saved some that would have died had they been potted in the standard 1 gallon black plastic pots filled with MVP instead. Nothing else in my control appears to have had any bearing on whether trees lived or died.

The chances that I have a group of 8 trees, two of which are dead, and the other group of 8 also has 2 4 dead (total 4 6 dead trees in 16) is about 43% 24.5% - far and away the most likely outcome due to chance. So I conclude that the defoliation treatment had no role in causing 4 6 of my new seedlings to die.
On the other hand, it looks like the finer grained Turface Pro League Heritage Red in shallower, clear orchid pots was beneficial. All four Five of the dead seedlings were potted in 1 gallon black a plastic pots of Turface MVP whereas, no one seedling died that was potted in an orchid pot of Pro League. There is somewhat less than a 4% (3.846%) more than a 5% (5.594%) chance of all four five out of six being in one group by chance, so this result is still marginally indicated to be an effect of the treatment.
Putting 1 cm long vertical cuts spaced around the trunk base most likely did not have any effect on whether the seedlings died or not. Only 4 of the 16 trees got the treatment (12 did not) this spring and all 4 5 are still alive, and 1 died. There is a 27.2% 39.6% chance of having all four 5 of 6 dead trees assigned to the group of 12 just by luck of the draw, so I conclude these cuts no effect on the mortality of these seedlings.
Decandling stimulated adventitious buds that extended much like happens with Japanese black pines. Of the 6 seedlings that died, 3 were candle pruned and 3 were not; in other terms, candle pruning had no effect on seedling mortality.
I have decided that I will repot 8 trees this Aug/Sep becuase only 2 of the '-' repot seedlings are dead, I have two spare seedlings to replace them, and (at this point in the experiment) I am free to redefine '-' repot to be repotting in Aug/Sep.

Still:


These losses put a dent in my planned experiment. Clearly I have two choices:
  1. buy replacement trees
  2. reduce the experiment to an 8 tree design next spring
  3. abandon this (Lodgepole pine) experiment
I am undecided which to take. But, I do have 3 extra seedlings that can replace the 3/4 of the dead trees were slated for Aug/Sep repotting. So, I may do not need to decide until sometime this winter.
 
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0soyoung

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Initial Potting Effects - other possible quantitative factors

Potting order does not seem to have affected which seedling are living or are now dead. The following table lists the seedling status in order of potting (from left to right).

potting order1[sup]st[/sup]2[sup]nd[/sup]3[sup]rd[/sup]4[sup]th[/sup]5[sup]th[/sup]6[sup]th[/sup]7[sup]th[/sup]8[sup]th[/sup]9[sup]th[/sup]10[sup]th[/sup]11[sup]th[/sup]12[sup]th[/sup]13[sup]th[/sup]14[sup]th[/sup]15[sup]th[/sup]last
statedieddieddeaddieddied
][/td]
There is no sytematic pattern here, so it is not likely that seedlings died because of the order in which they were potted. In other words, things such as I left the roots exposed to air while the seedlings were sitting in line to be potted, say, caused seedlings to die are not supported by the data.

Nor is there any support for notions that the losses were due to seedling size instead of the indicated 'shallow clear pot + Pro League soil versus deeper pot of MVP effect' (see the previous post). There is no systematic pattern of the dead seedlings with respect to initial weight or base diameter which is illustrated by the graphical attachments.

LPweights.jpgLPdiams.jpg
 

0soyoung

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Initial Potting Effects – possible qualitative factors (1/4)

Maybe there is some factor that can be seen from the photos of the seedlings. These were taken as general record shots just before each seedling was placed into its respective pot. I could very well be overlooking something that is clear from the pictures, but I don’t see anything that would let me identify which seedlings were prone to die. If you can, please explain the factor you see that leads you to believe you can identify the four that died. I cannot.
 

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0soyoung

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Initial Potting Effects – possible qualitative factors (2/4)

Another 5 of the 16 experiment seedlings as they were just before being potted.
 

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0soyoung

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Initial Potting Effects – possible qualitative factors (3/4)

The third set of five:
 

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0soyoung

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Initial Potting Effects – possible qualitative factors (4/4)

The 16th lodgepole seedling
 

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0soyoung

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Trunk/stem Thickening

When I potted my lodgepoles this spring, I painted a mark about 10 cm (4 inches) above the soil level and used this site for measuring the trunk thickness of each seedling every week or two with an inexpensive digital caliper. Each time I measured the seedlings, I measured each three times so that I could also gage my measurement accuracy and, therefore, whether the individual trees were indeed thickening while I was making measurements during the season.

I’ve rendered my data on the attached chart by the average thickness measured across the 10 trees that survived this summer and have normalized the data to represent the fraction of the seasonal increment (i.e., the normalized average thickness at the end of the season is 1). I’ve also represented the standard error of my measurements by error bars on the attached chart.

For me, the most interesting thing that comes from this is the red dashed curve of the rate of thickening (the slope of the curve through the data points) which peaks ca. 27 June. This is very similar to my Douglas firs, cork oaks, and redbuds. I’ve attached plots of the growth rate curve with my daily air temperatures and daylight hours. As I commented in those other posts, scholarly papers suggest that this time of the maximum trunk thickening rate is controlled by daylight hours and the activation/dormancy of the cambium is controlled by temperature.
I should add are that my measurement accuracy was about 0.06mm (surprisingly good) and that the average thickness increment for my surviving lodgepole seedlings was about 1.85mm (which amounts to about a 40% average increase in thickness for this past growing season).
 

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0soyoung

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The Final Tally

I did manage to demonstrate that lodgepole pines can be repotted in Aug/Sep. But, because of the large seedling mortality rate, I did not generate any comparative data with seedlings repotted in ‘spring’. Little more came of this experiment – disappointing, but not a complete failure, IMO.

The final tally is that 9 of 16 seedlings died in the first season. Half of the seedlings randomly assigned to fall group died (#3, #9, #13, and #15) and 5 assigned to the spring group (#2, #4, #10, #12, and #14). There is no indication that any factor of the experiment was the cause (or cure). I used 3 extra seedlings (#17, #18, and #20, resp.) to replace #9, #13, and #15 when I did the first repot (RP1) of the ‘fall’ seedlings on 31 Aug 13. In November it became clear to me that ID#3 was dead as well, leaving me with only 7 seedlings in the group. These 7 grew well in the 2014 season and were repotted on 3 Sep 14:

IDrepotmediumcutsshoot
prune
shoot wt removedRP1 wt afterRP2 wt b4seasonal wt gainseasonal
+shoot
1---+12.1610291927.16
5--++46.4841190149195.48
7-++-35966161
9----291178888
11-+-+19.732562443.7
13--+- 32926060
15-+++16.91431056278.91

• Shoot prune (+) was on 17 Jun 14 --> shoot wt removed
• RePot1 was on 31 Aug 13 for fall repotting (-)
• RePot2 was on 3 Sep 14 for fall repotting (-)
• Weight removed in repotting is the difference between RP1 after and RP1 before.
• Seasonal weight gain is the response to the factors repot, medium, and cuts
o For fall (+) = (RP2 wt b4) – (RP1 wt after)​

I performed shoot pruning on the indicated seedlings (+) on 17 June 14 instead of waiting to do this during repotting. I collected and weighed the shoot cuttings, recording them in the table (above). This weight needs to be added to the ‘seasonal wt gain’ (as I have been using the term elsewhere) to properly account for the weight gained for the year. I pruned shoots, leaving a few rows of needles in a fashion similar to what is commonly done with most pines and spruce. The extent of my pruning can be seen by flicking back and forth between the attached [LP_b4Prune.jpg] and [LP_ftrPrune.jpg] (click on the photo in the display window to have it open in another tab where it can be viewed in closer detail). All of these set a new terminal bud whorl. In fact, the timing was early enough to have the new terminal bud flush in August [see LP1_2014-08-28.jpg]. However, I haven’t noticed any fascicular back budding (i.e., all candle buds are in the terminal whorls; none are apparent on internode stems).

Neither basal trunk cuts nor the pot-medium had any apparent effect. Again, I am looking at the differences between the ‘-‘ treated seedlings and the ‘+’ treated ones, on average, or as a group. Even if one is using formulaic statistical analysis, it pays to look at the data graphically, which is about all we really need here. I’ve made a histogram of the ‘seasonal+shoot’ weight responses to having grown the seedlings in black pots of Turface MVP versus clear orchid pots of Pro League [see LPmedium.jpg]. ID#5 stands out, being unusually heavy compared to all the other seedlings. If we leave it aside, it is clear that the remainder of the trees in both groups is essentially alike, meaning it didn’t matter if the trees were grown in MVP or Pro League. Similarly, basal cuts had no effect on the annual weight gain.
 

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0soyoung

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You Can Too

You needn't live in Anacortes, WA to repot pinus contorta v. latifolia in late summer or fall as I have done. Anyone should be able to do similarly as long as root temperatures below 90F (33C) when they repot. In the week of repotting, relative humidity wasn’t below 50%, but repotting when it is below 50% may well be possible.

The cohesion tension theory is a well-established model of water transport in trees. The root membranes and the ‘series of tubes’ of xylem lumens are represented as a series of resistors. The water potential of the air versus the soil is analogous to the voltage difference in an electrical circuit that is the force that causes the flow of water (current) though the tree. With regard to repotting, we need only be concerned about the water potential of the air and the resistance we create by how badly we savage/ravage the roots.

For this experiment my methodology was to immerse the roots in a bucket of water and gently work out the Turface. I weighed the tree after patting the roots dry with a towel (B4). I then inverted a 1 gal. black plastic pot (identical to the ones used in the experiment) and used the bottom as a template to prune the roots. I combed only enough to draw out snags/snarls so as to have radial roots, taking care to not rip out fine ‘feeder’ roots. The mat was finally trimmed, again using the bottom of the pot template and the reweighed the tree (Ftr) before putting it back into its pot. Cutting off the bottom half to 2/3 of a root saturated pot, combing the perimeter, and analogously pruning the roots should be equivalent.

The water potential of the air is proportional to the Kelvin temperature of times the natural logarithm of the relative humidity. You don’t need to do any arithmetic, I've plotted some lines of constant water potential in the attached charts. The important point to note is that water potential is almost independent of temperature, over the range for which our trees are growing.

Our perceptions that higher temperature means more transpiration stress comes from the fact that on any given day, the relative humidity goes down as the air heats up. I've also plotted the temperature and relative humidity that were recorded every 5 minutes for a period of 7 days, starting with the day I repotted (F13 for fall 2013, F14 for fall 2014). Notice how this ‘cloud’ reflects the daily trend we all know so well of humidity going down as the air heats up and goes back up when the atmosphere cools down again at night (on any given day, transpiration stress is greatest in the afternoon).

Generally, the warmer it is the faster plants grow, up to a point. For temperate species, growth stops when the temperature climbs above 90F to 100F because metabolic activity is consuming all the food produced by photosynthesis and then some (i.e., there is nothing left over to make more tree). More importantly, however, trees cannot recover from repotting unless the roots can grow, which means they must be at a temperature below about 90F.

Repotting is possible at times other than 'as buds swell'.
 

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