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planation that Lemna rises to th
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Hi Steve & All,
Yes we can agree with the fact that they sink in the fall and rise=20
in the spring and, by analogy with plant processes in general one may=20
assume that these changes in position are under hormonal control. The=20
long rambling discussion last year was largely an attempt to consider=20
possible mechanisms. One may take it as given that photosynthesis=20
requires light and respiration continues under all conditions but slows=20
as temperature decreases. Also given; CO2 is more soluble in water than =20
O2.
Note that my control was the dish on the windowsill and treated was=20
the dish in darkness.
The original article proposed starch accumulation in the fall as the=
=20
mechanism of sinking and loss in the spring as the mechanism of rise.=20
Someone last year proposed an alternative;
The alternative being-- With shortening days in the fall and=20
consequently less photosynthesis, the cellular release of CO2 would=20
exceed the release of O2. And as photosynthesis approached zero, CO2=20
would predominate in the gas filled spaces. This reversal in gas=20
composition ( O2 > CO2) would render gas filled spaces, which were not=20
isolated from the medium, more subject to flooding due to the greater=20
solubility of CO2.
If the above reasoning had been valid then my treated plants, kept=20
in darkness for nearly a week, would have all sunk. They showed no=20
greater tendency to sink than the control. Consequently flooding of=20
intercellular spaces (or specialized aerenchyma) by water is not the=20
mechanism by which average density of Lemna increases in the fall.
So I conclude that accumulation of starch (density 1.5) in the fall,=
=20
as growth slows to zero and respiration slows as temperature lowers, is=20
the mechanism of sinking. And conversely greater respiration, due to=20
rising temperature and resumption of growth leads to loss of starch, a=20
decrease in average density and rise to the surface.
The original article noted that Lemna is more efficient than corn as=
=20
a producer of starch; impressive. I suspect the starch content in the=20
fall would be higher than in the spring and this I think is true of most=20
plans in temperate climates.
Yt, DW Kentville
------ Original Message ------
From: "Stephen Shaw" <srshaw@Dal.Ca>
To: "naturens@chebucto.ns.ca" <naturens@chebucto.ns.ca>
Sent: 9/28/2018 11:57:50 PM
Subject: Re: [NatureNS] Duckweed
>Hi Dave,
>I=E2=80=99d forgotten about this, but isn=E2=80=99t the primary observatio=
n to explain=20
>that the plants routinely sink in the winter and rise again in the=20
>spring? What the mechanism is, is an interesting but secondary=20
>consideration. In your =E2=80=98experimental=E2=80=99 case with lighted=
duckweed, it=20
>should be producing and accumulating some sort of gas mixture by=20
>September's photosynthesis, maybe plus some concurrent respiration. =20
>Your =E2=80=98control', dark duckweed, should have no photosythesic activi=
ty,=20
>so only respiration should produce any gas at all, presumably CO2.
>
>The problem is that neither =E2=80=98expt' nor =E2=80=98control' actually=
sank on Sept=20
>27. Since the plant material including any dense starch should anyway=20
>have an average density >1g/cc (i.e. greater than plain water*),=20
>excluding any gas spaces, both cases must still be floating according=20
>to some undissolved gas inclusions, though not necessarily the same mix=20
>of CO2/O2 in the two cases. You get an A+ for industry and design, but=20
>Lemna gets an F for cooperation.
>
>*Something I=E2=80=99d not considered that you may know about but I don=E2=
=80=99t is=20
>oil/fat production in plants, which obviously is important for some=20
>land plants (canola, sesame, olives etc). Oils have specific gravities=20
><1, around 0.9 g/cc, so enough oil volume could be sufficient to float=20
>a water plant without invoking gas spaces. If something dense like=20
>starch gets converted to an oil in spring, could that contribute, or is=20
>this just fantasy?
>
>Is it possible that the trigger for sinking, whatever its mechanism, is=20
>a particular drop in day length that had not yet been closely=20
>approached by Sept 27, and especially in your toasty living room=20
>(temperature might be another factor)? If you haven=E2=80=99t flushed th=
em in=20
>frustration, you should convey both your test subjects to an unheated=20
>outhouse and extend your experiment there at least to freeze-up.
>Steve
>---------------------------------------------------------
>On Sep 27, 2018, at 12:35 PM, David <dwebster@glinx.com> wrote:
>
>>Dear All,
>> I have had my eye open this summer for some Lemna to test the gas=20
>>composition idea; the more soluble CO2 predominating as days shorten=20
>>leading to flooding of gas spaces and sinking; photosynthesis=20
>>predominating in spring as days lengthen leading to flooded air spaces=20
>>being filled by less soluble O2 and rise to the surface.
>> And I was able to collect some on Sept 21 without having to wade=20
>>in muck of uncertain depth. So I set up a simple trial; some kept in=20
>>darkness, except for a few minutes daily for observation, and some=20
>>kept on a windowsill.
>> By Sept 27 those kept in darkness showed no tendency to sink but=20
>>were noticeably less green than those exposed to daylight and some=20
>>artificial light in the evening. This leads to the conclusion that=20
>>flooding of intercellular gas spaces when CO2 predominates does not=20
>>cause sinking of Lemna. The converse explanation that Lemna rises to=20
>>the surface in the spring when intercellular spaces become filled by=20
>>less soluble O2 is accordingly voided.
>> The explanation given in the link posted by Nancy on Oct 3, 2017=20
>>is consequently more sound. Starch accumulation in the fall. as=20
>>photosynthesis exceeds respiration at lowering temperature, leads to=20
>>sinking. Starch consumption, as temperature warm in the spring and new=20
>>buds start to grow, leads to rise to the water surface. [density of=20
>>starch is high; 1.5 g/cm^3]
>>
>>Yt, DW, Kentville
>>
>>
>>
>>------ Original Message ------
>>From: "Stephen Shaw" <srshaw@Dal.Ca>
>>To: "naturens@chebucto.ns.ca" <naturens@chebucto.ns.ca>
>>Sent: 3/10/2018 3:20:47 PM
>>Subject: Re: [NatureNS] Duckweed
>>
>>>Interesting puzzle, perhaps not so simple. Any cell system like a=20
>>>live leaf is bound to be somewhat denser than pond water, regardless=20
>>>of denser starch, so will naturally sink at all times unless kept=20
>>>buoyant by the extracellular gas bubbles or some other modification. =20
>>>What seems to need explaining is why the bubbles are maintained in=20
>>>summer (dissolved gases can pass through lipid cell membranes=20
>>>quickly, so you=E2=80=99d expect them to dissolve out into the surroundi=
ng=20
>>>pond), and why they disappear in winter. He doesn=E2=80=99t seem to kno=
w if=20
>>>it=E2=80=99s CO2 or O2 in the bubbles, or both. Perhaps they are largel=
y O2=20
>>>in summer and dissolve and normally pass out of the leaf to oxygenate=20
>>>the pond and dissolved CO2 moves in, but leaf photosynthesis is=20
>>>sufficiently high in summer to maintain them, despite these losses. =20
>>>In winter gas production simply stops, and the non-buoyant plants=20
>>>sink. As winter ends, respiration produces bubbles with a different=20
>>>gas, CO2, and they rise again then switch over to O2 as=20
>>>photosynthesis picks up.
>>>
>>>It therefore seems likely that these leaves have some special surface=20
>>>coating that slows down gas exchange with the pond. Maybe they still=20
>>>retain stomata under the leaf which normally facilitate gas exchange=20
>>>for leaves in air, but these are modified to block or regulate gas=20
>>>exchange in water? Maybe this is already known, just not to us here?
>>>Steve
>>>
>>>On Mar 10, 2018, at 10:45 AM, David <dwebster@glinx.com> wrote:
>>>
>>>>Hi Nancy & All,
>>>> I admit not having wondered about this but I think he makes a=20
>>>>simple process complicated. The air pockets to which he refers are=20
>>>>presumably intercellular spaces which in the absence of=20
>>>>photosynthesis presumably can become water filled. Starch has a=20
>>>>specific gravity of 1.5 g/mL and, in cooler weather starch will=20
>>>>accumulate when respiration slows more than photosynthesis and the=20
>>>>submarine will sink. With warming, growth resumes, respiration and=20
>>>>starch consumption rates increase and the submarine rises.
>>>>Yt, DW, Kentville
>>>>
>>>>------ Original Message ------
>>>>From: "nancy dowd" <nancypdowd@gmail.com>
>>>>To: naturens@chebucto.ns.ca
>>>>Sent: 3/10/2018 9:08:02 AM
>>>>Subject: [NatureNS] Duckweed
>>>>
>>>>>This is an interesting article on Duckweed seasonal disappearance=20
>>>>>and reappearance in the Spring 2018 issue of Northern Woodlands=20
>>>>>Magazine.https://northernwoodlands.org/outside_story/article/duckweed-=
migration
>>>>>
>>>>>I had never really thought about where it went in Fall or how it=20
>>>>>re-emerges in Spring. Such an important floating pond plant in=20
>>>>>productive fresh water
>>>>>
>>>>>Nancy D
>>>>>
>>>>>Sent from my iPad
>>>
>
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<body><div>Hi Steve & All,</div><div>=C2=A0 =C2=A0 Yes we can agree wit=
h the fact that they sink in the fall and rise in the spring and, by analog=
y with plant processes in general one may assume that these changes in posi=
tion are under hormonal control. The long rambling discussion last year was =
largely an attempt to consider possible mechanisms. One may take it as giv=
en that photosynthesis requires light and respiration continues under all c=
onditions but slows as temperature decreases. Also given; CO2 is more solub=
le in water than =C2=A0O2.</div><div>=C2=A0 =C2=A0 Note that my control was =
the dish on the windowsill and treated was the dish in darkness.</div><div=
>=C2=A0 =C2=A0 The original article proposed starch accumulation in the fal=
l as the mechanism of sinking and loss in the spring as the mechanism of ri=
se. Someone last year proposed an alternative;</div><div>=C2=A0 =C2=A0 =C2=
=A0The alternative being-- With shortening days in the fall and consequentl=
y less photosynthesis, the cellular release of CO2 would exceed the release =
of O2. And as photosynthesis approached zero, CO2 would predominate in the =
gas filled spaces. This reversal in gas composition ( O2 > CO2) would r=
ender gas filled spaces, which were not isolated from the medium, more subj=
ect to flooding due to the greater solubility of CO2.</div><div>=C2=A0 =C2=
=A0 If the above reasoning had been valid then my treated plants, kept in d=
arkness for nearly a week, would have all sunk. They showed no greater tend=
ency to sink than the control. Consequently flooding of intercellular space=
s (or specialized aerenchyma) by water is not the mechanism by which averag=
e density of Lemna increases in the fall.</div><div>=C2=A0 =C2=A0 So I conc=
lude that accumulation of starch (density 1.5) in the fall, as growth slows =
to zero and respiration slows as temperature lowers, is the mechanism of s=
inking. And conversely greater respiration, due to rising temperature and r=
esumption of growth leads to loss of starch, a decrease in average density=
and rise to the surface.</div><div>=C2=A0 =C2=A0 The original article noted =
that Lemna is more efficient than corn as a producer of starch; impressive=
. I suspect the starch content in the fall would be higher than in the spri=
ng and this I think is true of most plans in temperate climates.=C2=A0</div=
><div>Yt, DW Kentville=C2=A0</div>
<div><br /></div>
<div>------ Original Message ------</div>
<div>From: "Stephen Shaw" <<a href=3D"mailto:srshaw@Dal.Ca">srshaw@Dal.C=
a</a>></div>
<div>To: "naturens@chebucto.ns.ca" <<a href=3D"mailto:naturens@chebucto.=
ns.ca">naturens@chebucto.ns.ca</a>></div>
<div>Sent: 9/28/2018 11:57:50 PM</div>
<div>Subject: Re: [NatureNS] Duckweed</div><div><br /></div>
<div id=3D"xc5dd5f1fc8d549c" style=3D"word-wrap: break-word; -webkit-nbsp-m=
ode: space; -webkit-line-break: after-white-space;"><blockquote cite=3D"29C=
78FB6-68C5-425F-9729-ABA4EEDC204D@dal.ca" type=3D"cite" class=3D"cite2">
Hi Dave,
<div>I=E2=80=99d forgotten about this, but isn=E2=80=99t the primary observ=
ation to explain that the plants routinely sink in the winter and rise agai=
n in the spring? =C2=A0What the mechanism is, is an interesting but seconda=
ry consideration. =C2=A0 In your =E2=80=98experimental=E2=80=99 case with
lighted duckweed, it should be producing and accumulating some sort of gas =
mixture by September's photosynthesis, maybe plus some concurrent respirat=
ion. =C2=A0Your =E2=80=98control', dark duckweed, should have no photosythe=
sic activity, so only respiration should produce
any gas at all, presumably CO2.</div>
<div>=C2=A0=C2=A0</div>
<div>The problem is that neither =E2=80=98expt' nor =E2=80=98control' actua=
lly sank on Sept 27. =C2=A0Since the plant material including any dense sta=
rch should anyway have an average density >1g/cc (i.e. greater than plai=
n water*), excluding any gas spaces, both cases must still
be floating according to some undissolved gas inclusions, though not neces=
sarily the same mix of CO2/O2 in the two cases. =C2=A0You get an A+ for ind=
ustry and design, but
<i>Lemna</i> gets an F for cooperation.=C2=A0</div>
<div><br />
</div>
<div>*Something I=E2=80=99d not considered that you may know about but I do=
n=E2=80=99t is oil/fat production in plants, which obviously is important f=
or some land plants (canola, sesame,=C2=A0olives=C2=A0etc). =C2=A0Oils
have specific gravities <1, around 0.9 g/cc, so enough oil volume could =
be sufficient to float a water plant without invoking gas spaces. =C2=A0If =
something dense like starch gets converted to an oil in spring, could that =
contribute, or is this just fantasy? =C2=A0</div>
<div><br />
</div>
<div>Is it possible that the trigger for sinking, whatever its mechanism, i=
s a particular drop in day length that had not yet been closely approached=
by Sept 27, and especially in your toasty living room (temperature might be =
another factor)? =C2=A0 If you haven=E2=80=99t
flushed them in frustration, you should convey both your test subjects to=
an unheated outhouse and extend your experiment there at least to freeze-up=
.=C2=A0</div>
<div>Steve =C2=A0</div>
<div>---------------------------------------------------------<br />
<div>
<div>On Sep 27, 2018, at 12:35 PM, David <<a href=3D"mailto:dwebster@gli=
nx.com">dwebster@glinx.com</a>> wrote:</div>
<br class=3D"Apple-interchange-newline" />
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<div>
<div>Dear All,</div>
<div>=C2=A0 =C2=A0 I have had my eye open this summer for some Lemna to tes=
t the gas composition idea; the more soluble CO2 predominating as days shor=
ten leading to flooding of gas spaces and sinking; photosynthesis predomina=
ting in spring as days lengthen leading to
flooded air spaces being filled by less soluble O2 and rise to the surface=
.=C2=A0</div>
<div>=C2=A0=C2=A0=C2=A0=C2=A0And I was able to collect some on Sept 21 with=
out having to wade in muck of uncertain depth. So I set up a simple trial;=
some kept in darkness, except for a few minutes daily for observation, and=
some kept on a windowsill.=C2=A0</div>
<div>=C2=A0 =C2=A0 By Sept 27 those kept in darkness showed no tendency to=
sink but were noticeably less green than those exposed to daylight and some =
artificial light in the evening. This leads to the conclusion that floodin=
g of intercellular gas spaces when CO2 predominates
does not cause sinking of Lemna. =C2=A0The converse explanation that Lemna =
rises to the surface in the spring when intercellular spaces become filled =
by less soluble O2 is accordingly voided.</div>
<div>=C2=A0 =C2=A0 The explanation given in the link posted by Nancy on Oct =
3, 2017 is consequently more sound. Starch accumulation in the fall. as ph=
otosynthesis exceeds respiration at lowering temperature, leads to sinking. =
Starch consumption, as temperature warm in
the spring and new buds start to grow, leads to rise to the water surface. =
[density of starch is high; 1.5 g/cm^3]</div>
<div>=C2=A0 =C2=A0=C2=A0</div>
<div>Yt, DW, Kentville</div>
<div><br />
</div>
<div>=C2=A0 =C2=A0=C2=A0</div>
<div><br />
</div>
<div>------ Original Message ------</div>
<div>From: "Stephen Shaw" <<a href=3D"mailto:srshaw@Dal.Ca">srshaw@Dal.C=
a</a>></div>
<div>To: "<a href=3D"mailto:naturens@chebucto.ns.ca">naturens@chebucto.ns.c=
a</a>" <<a href=3D"mailto:naturens@chebucto.ns.ca">naturens@chebucto.ns.=
ca</a>></div>
<div>Sent: 3/10/2018 3:20:47 PM</div>
<div>Subject: Re: [NatureNS] Duckweed</div>
<div><br />
</div>
<div id=3D"x20c912178f194f2" style=3D"word-wrap: break-word; -webkit-nbsp-m=
ode: space; -webkit-line-break: after-white-space;">
<blockquote cite=3D"x-msg://4/F3FE0AE5-B951-4A4A-9575-4CE98894C7CA@dal.ca"=
type=3D"cite" class=3D"cite2">
Interesting puzzle, perhaps not so simple. =C2=A0Any cell system like a liv=
e leaf is bound to be somewhat denser than pond water, regardless of denser =
starch, so will naturally sink at all times unless kept buoyant by the ext=
racellular gas bubbles or some other
modification. =C2=A0What seems to need explaining is why the bubbles are m=
aintained in summer (dissolved gases can pass through lipid cell membranes=
quickly, so you=E2=80=99d expect them to dissolve out into the surrounding=
pond), and why they disappear in winter. =C2=A0He
doesn=E2=80=99t seem to know if it=E2=80=99s CO2 or O2 in the bubbles, or=
both. =C2=A0Perhaps they are largely O2 in summer and dissolve and normally =
pass out of the leaf to oxygenate the pond and dissolved CO2 moves in, but =
leaf photosynthesis is sufficiently high in summer to
maintain them, despite these losses. =C2=A0In winter gas production simply =
stops, and the non-buoyant plants sink. =C2=A0As winter ends, respiration=
produces bubbles with a different gas, CO2, and they rise again then switch =
over to O2 as photosynthesis picks up. =C2=A0=C2=A0
<div><br />
</div>
<div>It therefore seems likely that these leaves have some special surface=
coating that slows down gas exchange with the pond. =C2=A0Maybe they still=
retain stomata under the leaf which normally facilitate gas exchange for le=
aves in air, but these are modified to
block or regulate gas exchange in water? =C2=A0Maybe this is already known=
, just not to us here?</div>
<div>Steve =C2=A0=C2=A0<br />
<br />
<div>
<div>On Mar 10, 2018, at 10:45 AM, David <<a href=3D"mailto:dwebster@gli=
nx.com">dwebster@glinx.com</a>> wrote:</div>
<br class=3D"Apple-interchange-newline" />
<blockquote type=3D"cite" class=3D"cite">
<div style=3D"font-family: Tahoma; font-size: 12pt; font-style: normal; fon=
t-variant: normal; font-weight: normal; letter-spacing: normal; line-height=
: normal; orphans: auto; text-align: start; text-indent: 0px; text-transfor=
m: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text=
-stroke-width: 0px;">
<div>Hi Nancy & All,</div>
<div>=C2=A0 =C2=A0 I admit not having wondered about this but I think he ma=
kes a simple process complicated. The air pockets to which he refers are pr=
esumably intercellular spaces which in the absence of photosynthesis presum=
ably can become water filled. Starch has a
specific gravity of 1.5 g/mL and, in cooler weather starch will accumulate =
when respiration slows more than photosynthesis and the submarine will sin=
k. With warming, growth resumes, respiration and starch consumption rates i=
ncrease and =C2=A0the submarine rises.</div>
<div>Yt, DW, Kentville</div>
<div><br />
</div>
<div>------ Original Message ------</div>
<div>From: "nancy dowd" <<a href=3D"mailto:nancypdowd@gmail.com">nancypd=
owd@gmail.com</a>></div>
<div>To:<span class=3D"Apple-converted-space">=C2=A0</span><a href=3D"mailt=
o:naturens@chebucto.ns.ca">naturens@chebucto.ns.ca</a></div>
<div>Sent: 3/10/2018 9:08:02 AM</div>
<div>Subject: [NatureNS] Duckweed</div>
<div><br />
</div>
<div id=3D"xd49ec0a2bdf4406">
<blockquote cite=3D"x-msg://1/A593EEEC-616D-49BA-B70F-CA21003EAEDB@gmail.co=
m" type=3D"cite" class=3D"cite2" style=3D"margin-left: 5px; margin-right: 0=
px; padding-left: 10px; padding-right: 0px; border-left-width: 1px; border-=
left-style: solid; border-left-color: rgb(204, 204, 204); margin-top: 3px;=
padding-top: 0px;">
This is an interesting article on Duckweed seasonal disappearance and reapp=
earance in the Spring 2018 issue of Northern Woodlands Magazine.<a href=3D"=
https://northernwoodlands.org/outside_story/article/duckweed-migration">htt=
ps://northernwoodlands.org/outside_story/article/duckweed-migration</a>
<div><br />
</div>
<div>I had never really thought about where it went in Fall or how it re-em=
erges in Spring.=C2=A0<span style=3D"background-color: rgba(255, 255, 255,=
0);">Such an important floating pond plant in productive fresh water=C2=A0<=
/span><br />
<div><br />
</div>
<div>Nancy D<br />
<br />
<div>Sent from my iPad</div>
</div>
</div>
</blockquote>
</div>
</div>
</blockquote>
</div>
<br />
</div>
</blockquote>
</div>
</div>
</blockquote>
</div>
<br />
</div>
</blockquote></div>
</body></html>
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