1. Direct and indirect effects of global change on species responsiveness, invasion success and weed performance in dry regions
José M. Grünzweig
Robert H. Smith Faculty of Agriculture, Food and Environment, the Hebrew University of Jerusalem, Israel
2nd International Conference on «Novel and sustainable weed management in arid and semi-arid agro-ecosystems», Santorini, Greece, 8 September 2009

2. Outline
Global change as a complex concept in ecology, agronomy and plant science
Responsiveness to global change of plant species in general and weeds in particular
Invasive species in natural and agricultural ecosystem under global change
Conclusions: Weed success and invasion at different spatial scales in arid and semi-arid regions under future changed conditions

4. 1. Global change as a complex concept in ecology, agronomy and plant science
U.S. Global Change Research Act of 1990
Public Law (11/16/90) 104 Stat
"Global change" means changes in the global environment (including alterations in climate, land productivity, oceans or other water resources, atmospheric chemistry, and ecological systems) that may alter the capacity of the Earth to sustain life.

5. Change in atmospheric composition
Climate change
Nitrogen deposition
Change in stratospheric ozone
Tropospheric ozone pollution
...
Atmospheric CO2 enrichment

6. Land use change and anthropogenic disturbance

7. Alien species invasion
A. Danin
A. Danin
Barry A. Rice

8. 2. Responsiveness to global change of plant species in general and weeds in particular
Differential response of species and possible mechanisms underlying those responses
Potential relevance for agricultural weeds

9. Differential impact of global change on plant species
Global change manipulation in a ‘natural’ grassland in California:
Atmospheric CO2 enrichment (C)
Climatic warming (W)
Rain (precipitation) addition (P)
Atmospheric nitrogen deposition (N)
Species
 = increase
 = decrease
= inconsistent response
0 = no change 
Modified from Zavaleta et al Ecol. Monogr.

10. Onobrychis crista-galli
Impact of global change on plant species: example from a semi-arid community under atmospheric CO2 enrichment
100
200
300
Aboveground biomass (g m-2)
280
440
600
CO2 concentration (ppm) b a -5 5 10 15 20 25
Onobrychis crista-galli
P = 0.009
P.f.
M.m.
C.d.
H.c.
B.f.
P.p.
C.a.
P.co.
B.a.
P.a.
D.s.
B.l.
Bi.d.
A.s.
M.t.
H.s.
S.c.
T.c.
R.s.
H.u.
R.p.
D.g.
P.cr.
Br.d.
R.a.
S.p.
Species
Change in aboveground biomass (g·m-2)
Grünzweig & Körner Oecologia. Grünzweig & Körner Oikos

11. Respiration rate (differences between different plant parts)
Some growth-determining plant factors that can be altered by elevated CO2
Photosynthetic rate
Stomatal conductance
Respiration rate (differences between different plant parts)
Partitioning of dry matter (leaf vs. stem, roots or storage organs)
Leaf duration (leaf senescence)
Allocation of carbon to symbionts and exudation
0.0
0.1
0.2
0.3
0.4
280
440
600
CO2 concentration (ppm)
LWRa
Leaf weight ratio (LWRa = leaf
DW / total aboveground DW)
for Onobrychis crista-galli

12. Water saving under atmospheric CO2 enrichment as indirect effect on plant performance and species composition 28 39 7
Low CO2
High CO2
Evapotranspiration
Rain
Soil moisture
Water leaching
Period during growing season
Morgan et al Oecologia
Onobrychis crista-galli: the largest species and the most mesic legume in the community

13. Seed production at elevated CO2
Onobrychis crista-galli
Parentucellia flaviflora
Seed production (no. m-2)
CO2 concentration (ppm)
400
800
1200
280
440
600
P = 0.010
200000
400000
600000
280
440
600
CO2 concentration (ppm)
P = 0.001
Legume response as a consequence of more pods per plant. Wild cereals not or negatively affected
A. Danin

14. Competition between a semi-arid C4 pasture grass and an invasive C3 weed under atmospheric CO2 enrichment
P.h.:C.c. = 1:1
Cenchrus ciliaris
introduced C4 pasture grass in semi-arid subtropical and tropical pastures of northern Australia
Parthenium hysterophorus
invasive C3 weed
P.h.:C.c. = 1:3
Potential causes of increased growth and reproduction of P. hysterophorus under elevated CO2:
Plant water savings and accelerated plant development under conditions of rapid soil drying

15. Invasive weeds under past and future atmospheric CO2 enrichment
Increase in total biomass (%)
Potential causes of increased growth under elevated CO2:
Substantial belowground sinks contributing to largely stimulated plant growth
→ potential link between invasiveness and CO2 responsiveness
Ziska J. Exp. Bot.

16. Hemiparasite performance under global change
Phoenix & Press Folia Geobot.

17. Responses of C3 and C4 species to global change
Atmospheric CO2 enrichment
Higher sensitivity of C3 vs. C4 photosynthesis to elevated CO2
Stimulation of C4 relative to C3 species by elevated CO2 under warm and dry conditions
Climate change
Global warming: favors C4 plants in general
Timing of global warming:
Warmer winters → stimulation of C3 plants
Warmer and wetter summers → stimulation of C4 plants
Warmer and drier summers → suppression of C4 plants (unless fire plays a role in the ecology of the site)

18. 3. Species invasiveness in natural and agricultural ecosystems under global change
Lectures to be learned from natural ecosystems and potential application to invasive weeds in an agricultural context

19. Skinner et al Weed Sci.

20. Enhancement of an invasive annual grass under atmospheric CO2 enrichment in the desert
Success of the invasive alien Bromus madritensis spp. rubens in the Mojave Desert FACE experiment
Smith et al Science

21. Positive feedback loops of alien plant invasion
Invasive alien cheatgrass (Bromus tectorum)
Yield losses and costs for weed control (W USA, Canada): US$ million/year
Anthropogenic activity: heavy grazing, frequent tillage, fire
Positive feedback loop: Disturbance – Bromus biomass – large amount of flammable material – fire – promotion of Bromus and suppression of native perennial species
Evans et al Ecol. Appl.

22. Mediterranean islands

23. Plant invasion on Mediterranean islands
Human-dominated habitats
Habitat
Fig. 4. Number of alien species occurring in different Mediterranean island habitats. Human-dominated habitats are highlighted by dark shading.
Modified from Hulme et al In: Tokarska-Guzik et al., Backhuys Publishers

24. Impact of climate and land use on plant invasions
Oxalis pes-caprae invasion on the island of Crete (Greece)
Barry A. Rice
Initial bulbil biomass
Agricultural sites colonized by Oxalis pes-caprae
Ross et al Persp. Plant Ecol. Evol. Syst.

25. Model output on the effect of disturbance frequency on native and invasive species on the island of Lesbos (Greece)
Quercus ilex
Quercus coccifera
Juniperus oxycedrus
Ailanthus
altissima
Gritti et al J. Biogeogr.

26. Model output on the effect of disturbance frequency on native and invasive species on the island of Lesbos (Greece)
Ailanthus altissima (invasive tree)
Amaranthus retroflexus (invasive C4 herb)
Plantago lanceolata (native herb)
Different native trees and shrubs
Gritti et al J. Biogeogr.

27. Theory of alien invasions can suggest causes for successful invasive weeds
a) Increased resource availability
b) Enemy release
Invasive species
Keane & Crawley. 2002
Davis J. Ecol.
Blumenthal Science
Combination of a) and b)

28. 4. Conclusions: Weed success and invasion at different spatial scales in arid and semi-arid regions under future changed conditions

29. High responsiveness to global change
Ecophysiological topics
Large aboveground or belowground sinks
Efficient carbon allocation and canopy development
Rainfed agriculture
Water waster in a water-saving system
Accelerated growth and development
C4 weeds
Higher water use efficiency
Better adapted to elevated temperatures and heat stress than C3 plants
Hemiparasites
Effects of host water, carbon and nutrient relations

30. Plant invasiveness and site conditions prone to invasion
Drying → gaps in the vegetation as opportunity for establishment and integration
Land use change, fire and disturbance → extensive opportunity for establishment and integration under increased resource availability, leading to high propagule pressure
High propagule pressure → spread
Warming → competitive advantage (C4) for integration and spread
Elevated CO2 → competitive advantage (species with large seed or belowground sinks) for integration and spread

31. Thank you!