Supporting Information Notes S1–S3
Notes S1 The discovery of photoperiodism by G. Klebs (1914).
Klebs G. 1914. Über das Treiben der einheimischen Bäume, speziell der Buche. Abhandl.
Heidelberger Akad. Wiss. (Math. Nat. Kl.), No. 3, 1–112.
This unusually long, pioneering paper is hard to read - even for a German-speaker. It
was not quoted in the scientific English literature until 20 yr after its publication. Even
then citations did not convey Klebs’ experimental evidence for the control of bud
dormancy by the seasonality of insolation. The following detailed summary is apparently
the first one published in English. We therefore give page numbers of the original paper
for the observations summarized below.
Experiments done in autumn 1913
All potted experimental beech (Fagus sylvatica) plants were dormant in September, but
had some green leaves when they were moved to the “light chamber”, a dark room
illuminated continuously by electric light bulbs.
Experiments with saplings and seedlings
In Exp. 1 -4 dormant beech plants were placed into light chamber
progressively later.
Legend:
Light chamber
Greenhouse O O Dormant
♠ ♠ Flushing
Degree of dormancy:↓ +14 d = bud break after 14 d in light chamber
S
O
↓ +14d
Exp. 1
p.17-19
O O
N
D
J
F
↓ +32d
M
♠ ♠ ♠ ♠O O O O O O O O O O O O ♠ ♠ ♠ ♠
Conclusion: Bud expansion is inhibited by short days in October - December
S
O
N
D
J
F
M
Exp. 2
↓ +21d
↓ +28d
p.37
O O O ♠ ♠ ♠ ♠O O O O O O O ♠ ♠ ♠ ♠
Conclusion: Repeated transfers between autumnal short days and continuous
light result in alternating periods of rest and shoot growth.
Borchert et al., Insolation
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Supporting Information
S
O
N
Exp. 3
p.20-25
Fig. S1a
O O O O
D
↓ +33 d
J
F
M
♠♠♠♠♠♠♠♠♠♠♠♠♠♠♠♠♠♠
15 new leaves expand during continous growth over four months.
Conclusion: Saplings have the potential for continuos growth.
S
O
N
D
Exp. 4
p.37-38
Fig. S1b
O O O O O O
J
F
M
↓ +39d
↓ +32d
♠♠
♠♠
↓ +42d
♠♠
Conclusions: Under continuous light shoots may alternate between
bud break and rest.
Exp. 1 - 4
Conclusions: With declinind day length in autumn, the number of long days
required to induce bud break increases from 14d to 39d, i.e ., saplings are
progressively more dormant.
Notes S1 figure Prolonged shoot growth induced by exposure of dormant Fagus
sylvatica (beech) to continuous light (a) Expansion of 15 leaves during 4-month-long
continuous shoot growth of a sapling (see Exp. 3). (b) Expansion of three consecutive
shoots. I, II, III – bases of three consecutive flushes (see Exp. 4; figures from Klebs, 1914).
Borchert et al., Insolation
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Supporting Information
Experiments with isolated stem segments standing in water
Exp. 5 (p. 54): Effect of day length: Oct. 5: cuttings placed into LC or GH > Oct. 20: bud
break in LC, but not in GH.
Conclusion: In autumn continuous light induces bud break, but natural short days do
not.
Exp. 6 (p.55-56): Effect of light intensity. Bud lengths observed at increasing distance
from the light bulb: 40 cm > 8 mm bud; 80 cm > 5 mm; 160 cm > 2 mm; 200 cm > 0 mm.
Conclusion: Bud break is a function of light intensity.
Exp. 7 (p.57-59) Effect of duration of light periods. Light bulbs located 25 cm over glass
vessels with cuttings. During dark periods vessels are covered by a dark box.
Treatment
Dec-Jan
Feb. 1
T6
6h
---
T12
12 h
-----
T15
15 h
T18
T24
18 h
24 h
Feb. 15 Mar. 5
---
to T24
-----
+++
+++
+++
Buds:
--- dormant
+++ open
Results:
1. In December/January T18 (18 h light-period) does not cause bud break, but by early
February dormancy has been broken.
2. T15 causes bud break by early March, but not in February.
3. T12 does not cause bud break by early February, but transfer from T12 to T24 breaks
dormancy within 2 wk.
Conclusion: Light quantity determines bud break.
General conclusions
Photoperiodic control of temperate trees under natural conditions
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Supporting Information
1. Beech buds become progressively more dormant in autumn as light quantity
(intensity x duration) and temperature decline.
2. In February increasing light quantity induces changes in dormant beech buds which
enable bud break as soon as temperature permits.
Shoot growth patterns of tropical and temperate trees
Experimental manipulation of beech reveals three general shoot growth patterns of
trees:
1. Tropical trees: Continuous shoot elongation (see above Notes S1 figure (a)) or
2. periodic shoot elongation without formation of resting buds protected by bud
scales.
3. Temperate trees: Periodic shoot growth accompanied by the formation of resting
buds (see above Notes S1 figure (b)).
4.
Notes S2 Methods
In our earlier studies of tree phenology in Central American semi-deciduous forests we
observed trees biweekly for at least 2 yr. Such studies do not exist for equatorial forests.
We therefore analyzed information on tree phenology near the equator obtained from
the following sources: the Missouri Botanical Garden Herbarium (Borchert, 1996; Rivera
& Borchert, 2001); our short-term field observations made in Colombia and Uganda;
long-term field observations recorded earlier in the equatorial Amazon rainforest
(Alencar et al., 1979; Alencar 1990; Gautier & Spichiger, 1986); synchronous flushing
and flowering of canopy trees observed from low-flying aircraft; satellite-based remote
sensing records of periodic greening in equatorial rainforests in South America and
Africa (Huete et al., 2006; Mynemi et al., 2007; Guan et al., 2013).
We analyzed herbarium collections of 420 tree species represented in the Tropicos data
base of the Missouri Botanical Garden by more than 100 specimens. The majority of
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species are large evergreen trees, for which flowering specimens are quite rare. All
wide-ranging species represented by a good number of flowering specimens are
relatively small, easy-to-observe trees. They are semi-deciduous at higher latitudes,
where most flowering specimens were collected within 2–3 months during the dry
season (Fig. 1a–c). Near the equator flowering specimens are found throughout the
year, i.e., the flowering periodicity is not as distinct as at higher latitudes and we show
only values exceeding 5% of the total flowering herbarium collections of a species. For
most semi-deciduous species the number of flowering specimens collected near the
equator is too small to reveal distinct flowering periods. The relatively high number of
herbarium specimens collected south of the equator in Ecuador and Bolivia, and the
scarcity of collections from Colombia and Peru reflect differences in collecting activity,
not species distribution.
Notes S3 Molecular controls of tree development
Synchronous bud break and flowering of the tropical tree species analyzed here are
therefore likely to be manifestations of FT- control. Bud break induced by increasing
insolation in February/March has been observed in heated glasshouses at temperate
latitudes (Klebs, 1914), in temperate tree species growing in tropical Mexico (Borchert
et al., 2005) and in evergreen trees at all tropical latitudes (Fig. 3b). FT is also likely to
control flushing during both periods of increasing insolation near the equator (Fig. 1c)
and the latitudinal variation of flushing time in Guazuma (Fig. 2a,b). Lastly, both the FTcontrolled onset of dormancy in Populus and autumn-flowering of many tropical trees
are induced by declining photoperiod and start progressively later with declining
latitude (Böhlenius et al., 2006; Calle et al., 2010). Thus, the molecular mechanisms of
photoperiodic control of tree development are likely to be the same in temperate and
tropical trees.
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