Re[2]: [NatureNS] Duckweed

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From: nancy dowd <nancypdowd@gmail.com>
Date: Mon, 12 Mar 2018 18:52:23 -0300
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 year..whereas other years it was everywhere.&lt;div&gt;&lt;br&gt;&lt;/div&gt;&lt;div&gt;He

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Interesting. That must have had something to do with the drought conditions d=
uring the growing season in 2016 (?). =20

Nancy

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> On Mar 12, 2018, at 2:40 PM, Helene Van Doninck <helene.birdvet@gmail.com>=
 wrote:
>=20
> Having raised many waterfowl chicks at CWRC last summer, we always include=
 duckweed in their diet and we had to look HARD for it last year..whereas ot=
her years it was everywhere.
>=20
> Helene
>=20
> Helene Van Doninck DVM
> Cobequid Wildlife Rehabilitation Centre
> 2220 Irwin Lake Rd Brookfield NS Canada B0N1C0
> 902-893-0253
> helene.birdvet@gmail.com
> www.cwrc.net
> Find us on Facebook and Twitter
> ****Wildlife Matters****
>=20
>=20
>> On Sat, Mar 10, 2018 at 5:42 PM, N Robinson <nrobbyn@gmail.com> wrote:
>> Interesting discussion - thank you!  =20
>>=20
>> And then there is Wikipedia re interesting research going on:  https://en=
.wikipedia.org/wiki/Lemnoideae
>>=20
>> "Duckweed is being studied by researchers around the world as a possible s=
ource of clean energy. In the United States, in addition to being the subjec=
t of study by the DOE, both Rutgers University and North Carolina State Univ=
ersity have ongoing projects to determine whether duckweed might be a source=
 of cost-effective, clean, renewable energy.[18][19] Duckweed is a good cand=
idate as a biofuel because it grows rapidly, produces five to six times as m=
uch starch as corn per unit of area, and does not contribute to global warmi=
ng.[20][21] Unlike fossil fuels, duckweed removes carbon dioxide from the at=
mosphere instead of adding it.[22]"
>>=20
>> Nancy
>>=20
>>=20
>>> On Sat, Mar 10, 2018 at 3:52 PM, David <dwebster@glinx.com> wrote:
>>> Hi Steven & All,
>>>     Good points.  Aquatic plants typically have specialized tissues of i=
nterconnected passages which are filled with gas when the plant is active an=
d I would expect this to be true of Lemna also. The relative solubility of C=
O2 and O2 in water is no doubt relevant; CO2 is 16.4 and 31.5 times as solub=
le in water as O2 at 0o C and 10oC respectively. So during the growing seaso=
n, photosynthesis would keep such aerenchyma filled with O2. With shorter da=
ys and less photosynthesis,  CO2 production by respiration (year round in al=
l living tissue night and day) would gradually exceed O2 production and lead=
 to a flooding of the ballast tanks as the CO2 dissolves; submarine down.=20=

>>>     No doubt details of the anatomy play a part but I would expect stoma=
ta if present to be on the upper surface.
>>> Yt, DW,Kentville
>>>    =20
>>>=20
>>> ------ 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
>>>=20
>>>> Interesting puzzle, perhaps not so simple.  Any cell system like a live=
 leaf is bound to be somewhat denser than pond water, regardless of denser s=
tarch, so will naturally sink at all times unless kept buoyant by the extrac=
ellular gas bubbles or some other modification.  What seems to need explaini=
ng is why the bubbles are maintained in summer (dissolved gases can pass thr=
ough lipid cell membranes quickly, so you=E2=80=99d expect them to dissolve o=
ut into the surrounding pond), and why they disappear in winter.  He doesn=E2=
=80=99t seem to know if it=E2=80=99s CO2 or O2 in the bubbles, or both.  Per=
haps 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 photosynthe=
sis is sufficiently high in summer to maintain them, despite these losses.  I=
n winter gas production simply stops, and the non-buoyant plants sink.  As w=
inter ends, respiration produces bubbles with a different gas, CO2, and they=
 rise again then switch over to O2 as photosynthesis picks up.  =20
>>>>=20
>>>> It therefore seems likely that these leaves have some special surface c=
oating that slows down gas exchange with the pond.  Maybe they still retain s=
tomata under the leaf which normally facilitate gas exchange for leaves in a=
ir, but these are modified to block or regulate gas exchange in water?  Mayb=
e this is already known, just not to us here?
>>>> Steve  =20
>>>>=20
>>>>> On Mar 10, 2018, at 10:45 AM, David <dwebster@glinx.com> wrote:
>>>>>=20
>>>>> Hi Nancy & All,
>>>>>     I admit not having wondered about this but I think he makes a simp=
le process complicated. The air pockets to which he refers are presumably in=
tercellular spaces which in the absence of photosynthesis presumably can bec=
ome water filled. Starch has a specific gravity of 1.5 g/mL and, in cooler w=
eather starch will accumulate when respiration slows more than photosynthesi=
s and the submarine will sink. With warming, growth resumes, respiration and=
 starch consumption rates increase and  the submarine rises.
>>>>> Yt, DW, Kentville
>>>>>=20
>>>>> ------ Original Message ------
>>>>> From: "nancy dowd" <nancypdowd@gmail.com>
>>>>> To: naturens@chebucto.ns.ca
>>>>> Sent: 3/10/2018 9:08:02 AM
>>>>> Subject: [NatureNS] Duckweed
>>>>>=20
>>>>>> This is an interesting article on Duckweed seasonal disappearance and=
 reappearance in the Spring 2018 issue of Northern Woodlands Magazine.https:=
//northernwoodlands.org/outside_story/article/duckweed-migration
>>>>>>=20
>>>>>> I had never really thought about where it went in Fall or how it re-e=
merges in Spring. Such an important floating pond plant in productive fresh w=
ater=20
>>>>>>=20
>>>>>> Nancy D
>>>>