PHYSIOLOGICAL STRESSES OF LIMBER PINE SEEDLINGS AT AND ABOVE TREELINE IMMEDIATELY FOLLOWING NATURAL AND EXPERIMENTALLY ADVANCED SNOWMELT PHYSIOLOGICAL
STRESSES OF LIMBER PINE SEEDLINGS AT AND ABOVE TREELINE IMMEDIATELY FOLLOWING NATURAL AND EXPERIMENTALLY ADVANCED SNOWMELT
1 3
Andrew B.
Andrew B. Moyes
B Moyes1, Matthew J. Germino
, Matthew JJ. Germino2, Lara M. Kueppers
, Lara M
M. Kueppers1, 3
(1) University of California, Merced, CA 95343, (2) US Geological Survey, Boise, ID 83706, (3) Lawrence Berkeley National Laboratory, Berkeley,
University of California Merced CA 95343 (2) US Geological Survey Boise ID 83706 (3) Lawrence Berkeley National Laboratory Berkeley CA 94720
CA 94720
Abstract: Treeline
Ab
t t T li positions are anticipated to shift uphill in response to climate warming, a prediction which depends on future seedling recruitment at and above the p iti
ti ip t d t hift phill i
p
t li t
i g, p di ti
hi h d p d
f t
dli g
it
t t d b
th
current distribution limits of subalpine trees. To examine the role of cold temperature in seedling establishment at treeline, we measured physiological performance of t di t ib ti li it f b lpi t
T
i th
l f ld t p t
i
dli g t bli h
t t t li
d phy i l gi l p f
f
limber pine seedlings after surviving their first winter in heated and ambient temperature plots within the Alpine Treeline Warming Experiment. Fluorometric
limber pine seedlings after surviving their first winter in heated and ambient temperature plots within the Alpine Treeline
Warming Experiment Fluorometric
measurements of maximum photosystem II efficiency (Fv/Fm) indicated severe photoinhibition
measurements of maximum photosystem II efficiency (F
) indicated severe photoinhibition 10 days following melt (F
10 days following melt (Fv/Fm near 0), but photoinhibition
near 0) but photoinhibition diminished over diminished over
the subsequent 10 days Over the same period seedlings showed highly variable degrees of moisture stress in midday stem water potentials (Ψ) associated with frost
the subsequent 10 days. Over the same period, seedlings showed highly variable degrees of moisture stress in midday stem water potentials (Ψ) associated with frost drought and freeze‐thaw embolism despite consistently abundant afternoon soil moisture Many seedlings would not exude water under maximum measurement
drought and freeze‐thaw embolism, despite consistently abundant afternoon soil moisture. Many seedlings would not exude water under maximum measurement pressure (Ψ < ‐5
pressure (Ψ < 5 MPa) across all sampling dates (including up to 60 days following melt), indicating high spatial variability in cold
MPa) across all sampling dates (including up to 60 days following melt) indicating high spatial variability in cold‐associated
associated moisture stress, and possibly moisture stress and possibly
limited xylem conduit refilling Net CO2 assimilation appeared to be independently limited by photoinhibition
limited xylem conduit refilling. Net CO
assimilation appeared to be independently limited by photoinhibition and moisture stress. Although these stresses were not and moisture stress Although these stresses were not
significantly impacted by the timing of snowmelt or whether seeds were sourced from high or low elevation provenances, the observation of severe cold stress indicates
significantly impacted by the timing of snowmelt or whether seeds were sourced from high or low elevation provenances, the observation of severe cold stress indicates that
that seedling establishment above treeline
h seedling
dl establishment
bl h
above
b
treeline
l will be sensitive to future patterns of snowmelt and air temperature. willll b
be sensitive to ffuture patterns off snowmelt
l and
d air temperature.
Cold
Warm
Absolute tree limit
Absolute
tree limit
Species
Species transition
p
transition
Background: Climate warming is predicted to shift mountain Background:
Climate warming is predicted to shift mountain
tree species distributions uphill This would depend on seedling
tree species distributions uphill. This would depend on seedling establishment in warmed sites at high elevation Previous work
establishment in warmed sites at high elevation. Previous work at our warming experiment sites found an importance of
at our warming experiment sites found an importance of summer soil moisture on seedling success at and above treeline
summer soil moisture on seedling success at and above treeline, but little evidence for cold limitation (Moyes et al. 2012, but little evidence for cold limitation (Moyes
et al 2012
Reinhardt et al 2011) However in those studies cold stress
Reinhardt et al. 2011). However, in those studies, cold stress was not evaluated during the coldest (“shoulder
was not evaluated during the coldest (
shoulder season
season”)) months. months
Comparison of minimum soil C
p i
f i i
il
t p t
temperature at 5‐10 cm depth at the t 5 10
d pth t th
t
two study sites. Vertical gray bars show t dy it
V ti l g y b
h
sampling periods for photosystem II sampling periods for photosystem
II
efficiency and water potential Average
efficiency and water potential. Average day of melt for 10 replicate plots is
day of melt for 10 replicate plots is shown with a large circle Small circles
shown with a large circle. Small circles show dates of first and last plots to
show dates of first and last plots to melt The treeline site (USA) melted a melt. The treeline
site (USA) melted a
few weeks later than the alpine site
few weeks later than the alpine site (
(ALP),
(ALP), and with a larger effect of the ) and
d with
h a larger
l
effect
ff off the
h
h i g
heating treatment on melt day and l d y d
minimum daily soil T. Alpine plots i i
d ily il T Alpi pl t
experienced sub‐freezing temperature p i
d bf
i gt p t
due to low insulating snow cover
due to low insulating snow cover caused by high wind over all plots
caused by high wind over all plots.
Al i (ALP)
Alpine (ALP)
Upper Subalpine (USA within treeline ecotone)
Upper Subalpine (USA, within treeline
Objective: to characterize photoinhibition
Obj
j ti
t h
t i ph t i hibiti and moisture stress d
it
t
experienced
experienced by overwintering seedlings at and beyond the i
d by
b overwintering
i
i seedlings
dli
at and
db
beyond
d the
h
upper elevation
upper elevation limits of trees under ambient and l
i limits
li i off trees under
d ambient
bi
and
d
experimentally
experimentally warmed conditions. Two seed source ll warmed
d conditions.
d
Two seed
d source
provenances were compared,
provenances were compared, collected from local low and high d collected
ll
d from
f
local
l l low
l and
d high
h h
elevation sources of limber pine to investigate genetic
elevation sources of limber pine to investigate genetic differentiation in susceptibility to spring cold stress
differentiation in susceptibility to spring cold stress. Methods: Methods:
‐ Infrared heaters suspended over 10 of 20 study plots at each Infrared heaters suspended
p
over 10 of 20 studyy p
plots at each
site: in upper
site: in upper subalpine (USA, within treeline
pp subalpine
p (USA
(
, within treeline ecotone) and ecotone)) and
in the alpine
in the alpine tundra (ALP)
p t ndra (ALP)
(
)
‐ Fluorescence measurement of maximum photosystem II Fl
t f
i
ph t y t
II
efficiency (F
ffi i y ((Fv//Fm)) at night
t ight
‐ Midday stem water potential (Ψ) using a pressure bomb
Midd y t
t p t ti l (Ψ)
( ) i g p
b b
‐ Net assimilation (A
N
i il i
(Anet) and dark respiration (R) with a Licor
) dd k
i i (R) i h Li
6400
‐ Tissue freezing point by differential thermal analysis
Tissue
i
f
freezing
i point
i by
b differential
diff
i l thermal
h
l analysis
l i
Results: Photoinhibition
Results:
Photoinhibition of maximum PSII efficiency was of maximum PSII efficiency was
associated with minimum temperature of the preceding two
associated with minimum temperature of the preceding two nights indicating temporary reductions of photosynthetic
nights, indicating temporary reductions of photosynthetic capacity Middday stem water potential
capacity. Middday
stem water potential varied strongly in the varied strongly in the
shoulder seasons often reflectingg severe moisture stress but
shoulder seasons, often reflecting severe moisture stress, but without association with measured soil temperature
without association with measured soil temperature and and
p
moist re ariables Tiss e ffree ing
moisture variables. Tissue freezing point was similar across gp
point as similar across
individuals, consistently near ‐7.85 °C. ff t
i di id l ,
i t tly
7 85 °C Provenance effects P
arising from genetic differences between the two elevation seed i i gf
g
ti diff
b t
th t
l ti
d
td t t d( t h
) S dli g i
d
sources were not detected (not shown). Seedlings in warmed aand ambient plots experienced similar amounts of cold stress.
da b
bie t plots
t e pe ie ced
d si ila a ou ts
t of cold
d stt ess
Impact of photoinhibition
Impact
off photoinhibition
h
hb
( reduced
(as
(as reduced maximum photosystem II efficiency (F
d d maximum photosystem
h
II efficiency
ff
( v/F
(F
/ m)) and water )) and
d water
stress (midday stem water potential (Ψ)) on net assimilation (A
( idd y
p
i l (Ψ))
( ))
i il i (A
( net)) and dark respiration (R) for d d k pi i ((R)) f
i di id l
individual seedlings. Low values of F
dli g L
l
f Fv//Fm i t d ith l
l
f i il ti
d
m were associated with low values of assimilation and respiration, while low water potential may have limited assimilation to a greater extent than pi ti , hil l
t p t ti l y h
li it d i il ti t g t
t t th
respiration A multiple regression approach will be used to identify relative limitations to
respiration. A multiple regression approach will be used to identify relative limitations to carbon balance by photoinhibition and water stress.
carbon balance by photoinhibition
and water stress
Top: Maximum photosystem II efficiency (F
Top:
Maximum photosystem II efficiency (Fv/Fm) was reduced in spring and fall ) was reduced in spring and fall
when
when nighttime minimum soil T at 5 cm depth fell below 5 h nighttime
h
minimum soill T at 5 cm depth
d h fell
f ll below
b l 5 °C
C in the preceding 2 in the
h preceding
d 2
nights, indicating strong photoinhibition
ights, i di
d cati g st o g photoi hibi
b tio o
of seedlings upon exposure to cold f seed
dli gs upo e posu e to cold
d
night sky and bright daytime sun. F
ight ky d b ight d yti
Fv//Fm rose to healthy/active levels (near 0.8) t h lthy// ti l l (
0 8))
over subsequent days. b q
td y
Below Middayy stem water p
Below: Midday stem water potential (Ψ) was variable across sites, treaments, potential (Ψ) was variable across sites treaments
and provenances without a clear association with minimum temperature or
and provenances, without a clear association with minimum temperature or time since melt Values of Ψ on the dotted line represent seedlings that did not
time since melt. Values of Ψ on the dotted line represent seedlings that did not exude water under maximum chamber pressure and may have lost hydraulic
exude water under maximum chamber pressure, and may have lost hydraulic conductivity
conductivity.
Photoinhibition (as reduced (as reduced
maximum photosystem II
maximum photosystem II efficiency (Fv/Fm)) and water efficiency (F
)) and water
stress (midday stem water
stress (midday stem water potential (Ψ) were not
potential (Ψ) were not correlated among seedlings
correlated among seedlings, indicating separate predisposing
indicating separate predisposing conditions.
conditions. Midday stem water potential was not strongly Midday
stem water potential was not strongly
associated with soil water content and was
associated with soil water content, and was likely affected by frost drought and formation
likely affected by frost drought and formation of freeze/thaw emboli as soils froze at night. ff
/h
b li
il f
igh
O l
Only some individuals within 1 m
i di id l ithi 1 2 study plots t d l t
were affected possibly indicating the
were affected, possibly indicating the importance of soil water availability at smaller
importance of soil water availability at smaller spatial scales.
spatial scales.
Tissue freezing point was near ‐7.85 °C for all Ti
f
i gp i
7 85 °C f
ll
individuals.
i di id l
Acknowledgements: This study was supported by the Office of Science (BER), U.S. Department of Energy. Thanks to Acknowledgements:
This study was supported by the Office of Science (BER) U S Department of Energy Thanks to
B
Brynne
L
Lazarus for running freezing point analysis and Nat Goodby
f
i f
i
i t
l i
d N t G db and Mike Koontz for field work assistance d Mik K
t f fi ld
k it
collecting nighttime fluorescence data.
co
ect g g tt e uo esce ce data
Citations: A B Moyes C Castanha M J Germino and L.M. Kueppers. 2012. Warming and the dependence of limber Citations: A.B. Moyes, C. Castanha, M.J. Germino
and L M Kueppers 2012 Warming and the dependence of limber
pine (Pinus
i ( i
fl
flexilis) establishment on summer soil moisture within and above its current elevation range. Oecologia, ili )
bli h
il
i
i hi
d b
i
l
i
O l i
K. Reinhardt, C. Castanha, M.J. Germino, and L.M. Kueppers. 2011. Ecophysiological variation in two provenances of K. Reinhardt, C. Castanha, M.J. Germino, and L.M. Kueppers. 2011. Ecophysiological
variation in two provenances of
Pinus flexilis seedlings across an elevation gradient from forest to alpine. Tree Physiology, 31(6): 615‐625.
seedlings across an elevation gradient from forest to alpine Tree Physiology 31(6): 615 625