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Grupo de Ecología del DesiertoGrupo de Ecología del DesiertoDepartamento de BiologíaDepartamento de Biología
Universidad Nacional de San JuanUniversidad Nacional de San Juan
Dr. Eduardo Pucheta – Prof. Titular Ecología, Dpto. Biol.Dr. Eduardo Pucheta – Prof. Titular Ecología, Dpto. Biol.
Lic. Yanina Ribas-FernándezLic. Yanina Ribas-Fernández - Becaria CONICET, Adscripta - Becaria CONICET, Adscripta
docentedocente
Lic. Laura Quevedo-RobledoLic. Laura Quevedo-Robledo - Becaria CONICET, Adscripta - Becaria CONICET, Adscripta
docentedocente
Lic. Victoria García - Lic. en Biología, Becaria FONCyT, Lic. Victoria García - Lic. en Biología, Becaria FONCyT,
Adscripta docenteAdscripta docente
Mario Gatica – Estudiante de Biología, Adscripto alumnoMario Gatica – Estudiante de Biología, Adscripto alumno
Octavio Gerlo – Estudiante de Biología, Adscripto alumnoOctavio Gerlo – Estudiante de Biología, Adscripto alumno
Influences of rainfall and vegetation Influences of rainfall and vegetation patches on persistent and transient patches on persistent and transient
seed banks in central Monte, seed banks in central Monte, ArgentinaArgentina
•Are density and identity of the germinable seed Are density and identity of the germinable seed bank (GSB) of annual plants dependent on bank (GSB) of annual plants dependent on previous rainfall?previous rainfall?
•Is there any interaction between rainfall and Is there any interaction between rainfall and microhabitat to control seed density and species microhabitat to control seed density and species identity in the GSB of annuals?identity in the GSB of annuals?
• How is the seed depletion process in transient How is the seed depletion process in transient seed banks?seed banks?
• Are seed depletion mechanisms rainfall-Are seed depletion mechanisms rainfall-dependent?dependent?
Seed production
and dispersal
Vegetation patches
Bare ground
Rainfall
Persistent and transient seed banks
Bottom-up filters
Top-down filters
Plant regeneration
2. Seed fate in the desert shrub 2. Seed fate in the desert shrub Bulnesia retamaBulnesia retama along a precipitation gradient in central Monte gradient in central Monte
±200 mm
rainfall gradient
1. Influences of interyear variability and microhabitat 1. Influences of interyear variability and microhabitat on the identity and density of the germinable seed on the identity and density of the germinable seed bank of annual plants in a sandy Monte desertbank of annual plants in a sandy Monte desert
Study site
We collected 3 composite soil samples 10 cm diameter and 5 cm depth on bare ground and under shrub patches (N=30) after seed rain for two years (May 2002 and July 2003)
We assessed the GSB in a greenhouse after cold treatment for 4 weeks.
MethodsMethods
Persistent seed bankPersistent seed bank1. Influences of interyear variability and microhabitat 1. Influences of interyear variability and microhabitat on the identity and density of the germinable seed on the identity and density of the germinable seed bank of annual plants in a sandy Monte desertbank of annual plants in a sandy Monte desert
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun7
13
19
24
30
Me
an
Te
mp
(°C
)
0
15
30
45
60
Ra
infa
ll (m
m)
118.4 mm17.7 °C
Médanos Grandes599 m31° 44' S68° 07' W
The interaction of growing season and microhabitat showed non-additive effects for species composition, resulting in four significant species-assemblages (MRPP).
Below-avg rainfall
75.1 mm (2001-2002)
Above-avg rainfall
138.9 mm (2002-2003)
Bare
g
rou
nd
Veg
eta
tion
p
atc
hes
Boopis sp., Tribulus terrestris, Gomphrena mendocina
Portulaca grandiflora, Sclerophylax arnottii, Chenopodium murale
Amaranthus standleyanus, Portulaca umbraticola,
Chenopodium papulosum
Persistent seed bankPersistent seed bank1. Influences of interyear variability and microhabitat 1. Influences of interyear variability and microhabitat on the identity and density of the germinable seed on the identity and density of the germinable seed bank of annual plants in a sandy Monte desertbank of annual plants in a sandy Monte desert
Some annual plant species showed indicator values (P<0.05) for different combinations of growing season and microhabitat type (Indicator species analysis).
Bare ground Under shrubs
2001-2002 2002-2003
Growing season
0
200
400
600
800
Seed n
um
ber
Bare ground Under shrubs
75.1 mm (Oct-Apr)
138.9 mm(Oct-Apr)
Despite there was no significant interaction between rainfall and microhabitat, there is an “apparent” interaction to be tested in the long-term.
New question Is there any effect of rainfall and microhabitat on the germinable fraction of the persistent seed bank?
J. Arid
En
viro. In
J. A
rid E
nviro
. In
pre
ssp
ress
Persistent seed bankPersistent seed bank1. Influences of interyear variability and microhabitat 1. Influences of interyear variability and microhabitat on the identity and density of the germinable seed on the identity and density of the germinable seed bank of annual plants in a sandy Monte desertbank of annual plants in a sandy Monte desert
ANOVA F p
Growing season 20.9 0.000
Microhabitat 11 0.001
G. season*microhabitat 3.12 0.08
Interyear variability was more important than microhabitat explaining seed bank density variation.
Transient seed bankTransient seed bank2. Seed fate in the desert shrub 2. Seed fate in the desert shrub Bulnesia Bulnesia
retamaretama along a precipitation gradient in gradient in central Montecentral Monte
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun7
13
19
24
30
Me
an
Te
mp
(°C
)
0
15
30
45
60
Ra
infa
ll (m
m)
118.4 mm17.7 °C
Médanos Grandes599 m31° 44' S68° 07' W
118.4 mm
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun0
8
15
23
30
Me
an
Te
mp
(°C
)
0
15
30
45
60
Ra
infa
ll (m
m)
San Martín653 m33° 08' S68° 41' W
154.5 mm17.04 °C
154.5 mm
329 mm
150 mm
118.4 mm
154.5 mm
329 mm
150 mm
Transient seed bankTransient seed bank2. Seed fate in the desert shrub 2. Seed fate in the desert shrub Bulnesia Bulnesia
retamaretama along a precipitation gradient in gradient in central Montecentral Monte
•Predispersal fruit losses
•Fruit dispersal
•Seed bank dynamics
•Postdispersal seed losses
MethodsMethods
On each location (4 independent On each location (4 independent Bulnesia retama Bulnesia retama populations) and for two years we installed 4 rain populations) and for two years we installed 4 rain gauges and selected 10 individuals and 10 gauges and selected 10 individuals and 10 adjacent bare soils, where we studied bimonthly:adjacent bare soils, where we studied bimonthly:•Branch exclusion
•Temporal counts up to >90% dispersal
•Soil samples
•Seed germination
Transient seed bankTransient seed bank2. Seed fate in the desert shrub 2. Seed fate in the desert shrub Bulnesia Bulnesia
retamaretama along a precipitation gradient in gradient in central Montecentral Monte
Predispersal fuit losses to consumers
Fruit consumption increased with time after fruit maturation (R2 = 0.12; F = 33.18; P = <0.0001) similarly in all 4 sites (F = 0.21; P = 0.886).
0 44 88 132 176
Days after fruit maturation
-107
-53
2
56
110
% fr
uit l
oss
Fruit consumption and time since fruit maturation
146 223 299 376 453
Annual Rainfall (mm)
-107
-55
-3
48
100
% fr
uit l
oss
Fruit consumption and rainfall
Annual rainfall did not explain fruit consumption (F = 0.29; P = 0.589).
How does fruit dispersal is?How does fruit dispersal is?
Dispersal slopes Dispersal slopes were year and site were year and site dependent, dependent,
But rainfall But rainfall correlated weakly correlated weakly with dispersal with dispersal (data not shown).(data not shown).
1 46 91 135 180
Days
0
25
50
75
100
% R
em
na
nt f
ruits
M. Grandes
1 46 91 135 180
Days
0
25
50
75
100
% R
em
na
nt f
ruits
Telteca
1 46 91 135 180
Days
0
25
50
75
100
% R
em
na
nt f
ruits
Pichi
1 46 91 135 180
Days
0
25
50
75
100
% R
em
na
nt f
ruits
Ñacuñán
ANOVA F p
Year 149.547 0.000
Sites 2.878 0.036
Dispersal time 925.242 0.000
Year*Sites 11.088 7,27E-07
Year*Dispersal time 115.517 0.000
Sites*Dispersal time 4.190 4,59E-05
Year*Sites*Dispersal time 3.687 0.0002
Bare soils Undercanopies
91 149 207 265 322
Rainfall (mm)
-30
106
243
379
515
See
d nu
mbe
r in
soi
l (/S
q m
)
Early seed bank
Bare soils Undercanopies
How does rainfall affect How does rainfall affect B. retama B. retama soil seed soil seed bank?bank?
Early seed bank Early seed bank increased their increased their density and density and spatial variance spatial variance with rainfall.with rainfall.
Accumulated Accumulated rainfall up to the rainfall up to the beginning of the beginning of the Autumn seems to Autumn seems to impose an upper impose an upper limit to the limit to the amount of seeds amount of seeds that could be that could be stored in soils.stored in soils.
Seed bank may Seed bank may reflect seed reflect seed production.production.
ANOVA F p
Microhabitat 65,1663448 2,6523E-13
Rainfall 6,66570134 7,9727E-07
Microhabitat*Rainfall 6,051341 3,4467E-06
Bare soils Undercanopies
146 223 299 376 453
Cumulated rainfall
-30
123
275
428
580
See
d nu
mbe
r in
soi
l (/S
q m
)
Late seed bank
Bare soils Undercanopies
How does rainfall affect How does rainfall affect B. retama B. retama soil seed soil seed bank?bank?
Late seed bank Late seed bank decreased their decreased their density and density and spatial variance spatial variance with rainfall.with rainfall.
Accumulated Accumulated rainfall imposed rainfall imposed an opposite an opposite upper limit to the upper limit to the amount of seeds amount of seeds that could be that could be stored in soils.stored in soils.
Late seed bank Late seed bank depletion may be depletion may be associated to associated to rainfall.rainfall.
ANOVA F p
Microhabitat 26,790 7,71E-07
Cumulated Rainfall 3,587 0,00139
Microhabitat*Cum Rainfall 2,345 0,02701
Bare soil Undercanopies
30 75 120 165 210
Rainfall last three months (Feb-Apr, mm)
0
25
50
75
100
% s
eed
germ
inat
ion
in s
oils
Early seed germination and rainfall
Bare soil Undercanopies
Is seed germination a mechanism Is seed germination a mechanism explaining seed loss? explaining seed loss?
Rainfall explained Rainfall explained seed germination in seed germination in early and late seed early and late seed banks.banks.
Seed germination was Seed germination was explained by rainfall explained by rainfall similarly in bare soils similarly in bare soils and in undercanopies.and in undercanopies.
Bare soil Undercanopies
70 140 210 280 350
Cumulated rainfall (mm)
0
25
50
75
100
% s
eed
germ
inat
ion
in s
oils
Late seed germination and rainfall
Bare soil Undercanopies
ANOVA Early SG F p
Microhabitat 2.846 0.093
Rainfall 161.667 0.000
Microhabitat*rainfall 1.952 0.066
ANOVA Late SG F p
Microhabitat 0,230 0,631
Rainfal 2,574 0,015
Microhabitat*rainfall 0,530 0,810
Bare soil Undercanopies
30 75 120 165 210
Rainfall last three months (Feb-Apr, mm)
0
25
50
75
100
% s
eed
germ
inat
ion
in s
oils
Early seed germination and rainfall
Bare soil Undercanopies
Is seed germination a mechanism Is seed germination a mechanism explaining seed loss? explaining seed loss?
Rainfall explained Rainfall explained seed germination in seed germination in early and late seed early and late seed banks.banks.
Seed germination was Seed germination was explained by rainfall explained by rainfall similarly in bare soils similarly in bare soils and in undercanopies.and in undercanopies.
Bare soil Undercanopies
70 140 210 280 350
Cumulated rainfall (mm)
0
25
50
75
100
% s
eed
germ
inat
ion
in s
oils
Late seed germination and rainfall
Bare soil Undercanopies
Linear regression N R² R²Aj CpMallows
Early SG 160 0,14 0,14 26,87
Cumulated rainfall
F = 26.03
P =<0.0001
Linear regression N R² R²Aj CpMallows
Late SG 160 0,03 0,03 6,39
Cumulated rainfall
F = 5.42 p = 0.02
Seed production
and dispersal
Vegetation patches
Bare ground
Rainfall
Persistent and transient seed bank
Bottom-up filters
Top-down filters
Plant regeneration
Predispersal seed losses
Fruit dispersal
Vegetation patches
Bare ground
Rainfall
Plant regeneration
Seed bank dynamics
Seed germination
Postdispersal seed losses
Top-down filtersFruit
consumption
Seedling consumption
Bottom-up filters
Microsite effects
Seedling establishme
nt
Influences of rainfall and microhabitat Influences of rainfall and microhabitat on persistent and transient seed banks on persistent and transient seed banks
in central Monte desertin central Monte desertGSB of annual plantsGSB of annual plants
Observed patterns in seed density and species identity Observed patterns in seed density and species identity
were related to the amount of rainfall in the previous were related to the amount of rainfall in the previous
growing season and to microhabitat typegrowing season and to microhabitat type
Seed fate in Seed fate in B. retamaB. retama shrubs shrubs
Predispersal seed loss was independent from rainfall, Predispersal seed loss was independent from rainfall,
but dependent on time since fruit maturation, but dependent on time since fruit maturation,
Microsites were important in determining soil seed Microsites were important in determining soil seed
densities, but they were unimportant for seed densities, but they were unimportant for seed
germination rates,germination rates,
Rainfall partially explained seed germination, but there Rainfall partially explained seed germination, but there
were more seeds in soils under higher rainfall, were more seeds in soils under higher rainfall,
suggesting an effect of rainfall on fruit production. suggesting an effect of rainfall on fruit production.
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