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Grupo de Ecología del Desierto Departamento de Biología Universidad Nacional de San Juan Dr. Eduardo Pucheta – Prof. Titular Ecología, Dpto. Biol. Lic.

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Presentation on theme: "Grupo de Ecología del Desierto Departamento de Biología Universidad Nacional de San Juan Dr. Eduardo Pucheta – Prof. Titular Ecología, Dpto. Biol. Lic."— Presentation transcript:

1 Grupo de Ecología del Desierto Departamento de Biología Universidad Nacional de San Juan Dr. Eduardo Pucheta – Prof. Titular Ecología, Dpto. Biol. Lic. Yanina Ribas-Fernández - Becaria CONICET, Adscripta docente Lic. Laura Quevedo-Robledo - Becaria CONICET, Adscripta docente Lic. Victoria García - Lic. en Biología, Becaria FONCyT, Adscripta docente Mario Gatica – Estudiante de Biología, Adscripto alumno Octavio Gerlo – Estudiante de Biología, Adscripto alumno

2 Influences of rainfall and vegetation patches on persistent and transient seed banks in central Monte, Argentina Are density and identity of the germinable seed bank (GSB) of annual plants dependent on previous rainfall?Are density and identity of the germinable seed bank (GSB) of annual plants dependent on previous rainfall? Is there any interaction between rainfall and microhabitat to control seed density and species identity in the GSB of annuals?Is there any interaction between rainfall and microhabitat to control seed density and species identity in the GSB of annuals? How is the seed depletion process in transient seed banks? How is the seed depletion process in transient seed banks? Are seed depletion mechanisms rainfall-dependent? Are seed depletion mechanisms rainfall-dependent?

3 Seed production and dispersal Vegetation patchesBare ground Rainfall Persistent and transient seed banks Bottom-up filters Top-down filters Plant regeneration

4 2. Seed fate in the desert shrub Bulnesia retama gradient in central Monte 2. Seed fate in the desert shrub Bulnesia retama along a precipitation gradient in central Monte ±200 mm rainfall gradient 1. Influences of interyear variability and microhabitat on the identity and density of the germinable seed bank of annual plants in a sandy Monte desert

5 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. Methods Persistent seed bank 1. Influences of interyear variability and microhabitat on the identity and density of the germinable seed bank of annual plants in a sandy Monte desert

6 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 ( ) Above-avg rainfall mm ( ) Bare ground Vegetation patches Boopis sp., Tribulus terrestris, Gomphrena mendocina Portulaca grandiflora, Sclerophylax arnottii, Chenopodium murale Amaranthus standleyanus, Portulaca umbraticola, Chenopodium papulosum Persistent seed bank 1. Influences of interyear variability and microhabitat on the identity and density of the germinable seed bank 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).

7 75.1 mm (Oct-Apr) 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 Enviro. In press Persistent seed bank 1. Influences of interyear variability and microhabitat on the identity and density of the germinable seed bank of annual plants in a sandy Monte desert ANOVAFp Growing season Microhabitat G. season*microhabitat Interyear variability was more important than microhabitat explaining seed bank density variation.

8 Transient seed bank 2. Seed fate in the desert shrub Bulnesia retama gradient in central Monte 2. Seed fate in the desert shrub Bulnesia retama along a precipitation gradient in central Monte mm mm 329 mm 150 mm

9 118.4 mm mm 329 mm 150 mm Transient seed bank 2. Seed fate in the desert shrub Bulnesia retama gradient in central Monte 2. Seed fate in the desert shrub Bulnesia retama along a precipitation gradient in central Monte

10 Predispersal fruit losses Fruit dispersal Seed bank dynamics Postdispersal seed lossesMethods On each location (4 independent Bulnesia retama populations) and for two years we installed 4 rain gauges and selected 10 individuals and 10 adjacent bare soils, where we studied bimonthly: Branch exclusion Temporal counts up to >90% dispersal Soil samples Seed germination Transient seed bank 2. Seed fate in the desert shrub Bulnesia retama gradient in central Monte 2. Seed fate in the desert shrub Bulnesia retama along a precipitation gradient in central Monte

11 Predispersal fuit losses to consumers Fruit consumption increased with time after fruit maturation (R 2 = 0.12; F = 33.18; P = <0.0001) similarly in all 4 sites (F = 0.21; P = 0.886). Annual rainfall did not explain fruit consumption (F = 0.29; P = 0.589).

12 How does fruit dispersal is? Dispersal slopes were year and site dependent, But rainfall correlated weakly with dispersal (data not shown). ANOVAFp Year Sites Dispersal time Year*Sites ,27E-07 Year*Dispersal time Sites*Dispersal time4.1904,59E-05 Year*Sites*Dispersal time

13 How does rainfall affect B. retama soil seed bank? Early seed bank increased their density and spatial variance with rainfall. Accumulated rainfall up to the beginning of the Autumn seems to impose an upper limit to the amount of seeds that could be stored in soils. Seed bank may reflect seed production. ANOVAFp Microhabitat65, ,6523E-13 Rainfall6, ,9727E-07 Microhabitat*Rainfall6, ,4467E-06

14 How does rainfall affect B. retama soil seed bank? Late seed bank decreased their density and spatial variance with rainfall. Accumulated rainfall imposed an opposite upper limit to the amount of seeds that could be stored in soils. Late seed bank depletion may be associated to rainfall. ANOVAFp Microhabitat26,7907,71E-07 Cumulated Rainfall3,5870,00139 Microhabitat*Cum Rainfall2,3450,02701

15 Is seed germination a mechanism explaining seed loss? Rainfall explained seed germination in early and late seed banks. Seed germination was explained by rainfall similarly in bare soils and in undercanopies. ANOVA Early SGFp Microhabitat Rainfall Microhabitat*rainfall ANOVA Late SGFp Microhabitat0,2300,631 Rainfal2,5740,015 Microhabitat*rainfall0,5300,810

16 Is seed germination a mechanism explaining seed loss? Rainfall explained seed germination in early and late seed banks. Seed germination was explained by rainfall similarly in bare soils and in undercanopies. Linear regressionN R²R²AjCpMallows Early SG1600,14 26,87 Cumulated rainfall F = P = < Linear regressionN R²R²AjCpMallows Late SG1600,03 6,39 Cumulated rainfall F = 5.42p = 0.02

17 Seed production and dispersal Vegetation patchesBare ground Rainfall Persistent and transient seed bank Bottom-up filters Top-down filters Plant regeneration

18 Predispersal seed losses Fruit dispersal Vegetation patchesBare ground Rainfall Plant regeneration Seed bank dynamics Seed germination Postdispersal seed losses Top-down filters Fruit consumption Seedling consumption Bottom-up filters Microsite effects Seedling establishment

19 Influences of rainfall and microhabitat on persistent and transient seed banks in central Monte desert GSB of annual plants Observed patterns in seed density and species identity were related to the amount of rainfall in the previous growing season and to microhabitat type Observed patterns in seed density and species identity were related to the amount of rainfall in the previous growing season and to microhabitat type Seed fate in B. retama shrubs Predispersal seed loss was independent from rainfall, but dependent on time since fruit maturation, Predispersal seed loss was independent from rainfall, but dependent on time since fruit maturation, Microsites were important in determining soil seed densities, but they were unimportant for seed germination rates, Microsites were important in determining soil seed densities, but they were unimportant for seed germination rates, Rainfall partially explained seed germination, but there were more seeds in soils under higher rainfall, suggesting an effect of rainfall on fruit production. Rainfall partially explained seed germination, but there were more seeds in soils under higher rainfall, suggesting an effect of rainfall on fruit production.

20 Future plans Influences of rainfall and microhabitat on persistent and transient seed banks in central Monte desert: a long-term study Muchas gracias!


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