Long-term Long-term implications of plant implications of plant invasions: the invasions: the significance of the significance of the soil seed bank soil seed bank [email protected]School of Biology and Environmental Science University College Dublin Margherita Gioria & Bruce Osborne The Invasive Species Ireland Forum 2009
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Long-term implications of plant invasions: the significance of the soil seed bank [email protected] School of Biology and Environmental Science.
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Long-term implications of Long-term implications of plant invasions: the plant invasions: the
significance of the soil significance of the soil seed bankseed bank
Understanding the potential long-term implications of plant invasions
changes in SSB must be examined
Species displacement from the vegetation
Reduce seed input
Formation of a large above- and below-ground biomass
Limitation mechanisms
Changes in conditions for germination
Reproductive strategies of resident species
Saturation
MechanismsMechanisms
Gioria 2007
ObjectivesObjectives
3 large herbaceous plant invaders:
Fallopia japonica var. japonica FJ
Gunnera tinctoria GT
Heracleum mantegazzianum HM
Seed bank of GT and HM Effects on the structure (diversity, composition,
and abundance) of resident SSB communities Comparative assessment of the effects of these
invaders
CharacteristicsCharacteristicsLarge stature, biomass, and litter
Reproduction: FJ: exclusively by vegetative means GT: sexual and asexual HM: exclusively by seeds
Reproductive potential: GT: 700,000 seeds per plant (Osborne
et al. 1991) HM: 10,000-20,000 fruits per plant
(Pyšek et al. 2007)
Residence time: FJ: 3-5 years GT: 30-50 years HM: 30-40 years
Methods Methods
Multi-site comparative approach 3 sites for each invader Comparable invaded and uninvaded areas 4 – 4m2 plots 5 soil cores 3 depths (0-5, 5-10, 10-15 cm) May and October Seedling emergence approach (Thomspon &
Grime 1979) Unheated greenhouses 240 samples per site
• 9,762 ± 390 SD seedlings m−2 in October• 0-5 cm• Synchronous germination• Requirement for chilling period
Transient seed bank
Gunnera tinctoria
Heracleum mantegazzianum
Impacts of GTImpacts of GT
Fig. 1. nMDS configurations representing SSB communities invaded by GT at three sites
May October
Impacts of HMImpacts of HM
May
Fig. 2. nMDS configurations representing SSB communities invaded by HM at three sites
October
Impacts of FJImpacts of FJ
Fig. 3. nMDS configurations representing SSB communities invaded by FJ at three sites
OctoberMay
Dominance GT Dominance GT
Fig. 4. Dominance-diversity curves based on SSB data collected in May and October at three sites
May October
Dominance HMDominance HM
May October
Fig. 5. Dominance-diversity curves based on SSB data collected in May and October at three sites
Dominance FJDominance FJ
May October
Fig. 6. Dominance-diversity curves based on SSB data collected in May and October at three sites
SSB invaded by GTSSB invaded by GT
May
Figure 7. Similarity percentages analysis showing the species that most contributed to similarities between invaded seed bank communities at sites invaded by GT (Bray-Curtis, 4rt root tramsformed data)
SSB invaded by HMSSB invaded by HM
Figure 8. Similarity percentages analysis showing the species that most contributed to similarities between invaded seed bank communities at sites invaded by HM (Bray-Curtis, 4rt root tramsformed data)
SSB invaded by FJSSB invaded by FJ
May
Figure 8. Similarity percentages analysis showing the species that most contributed to similarities between invaded seed bank communities at sites invaded by FJ (Bray-Curtis, 4rt root tramsformed data)
Effect of invasive species Effect of invasive species identityidentity