Grupo de Ecología del Desierto Departamento de Biología Universidad Nacional de San Juan Dr....

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


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


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


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


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



•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



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


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


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


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


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.


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


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


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


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.


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


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.

Future plans Future plans 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 desert: in central Monte desert: a long-term studya long-term study

Muchas gracias!Muchas gracias!

Grupo de Ecología del Desierto Departamento de Biología Universidad Nacional de San Juan Dr....

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