Direct and indirect effects of global change on

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 2 International Conference on «Novel and sustainable weed management in arid and semi-arid agro-ecosystems» , Santorini, Greece, 8 September 2009 nd

Outline 1. Global change as a complex concept in ecology, agronomy and plant science 2. Responsiveness to global change of plant species in general and weeds in particular 3. Invasive species in natural and agricultural ecosystem under global change 4. Conclusions: Weed success and invasion at different spatial scales in arid and semi-arid regions under future changed conditions

1. Global change as a complex concept in ecology, agronomy and plant science U. S. Global Change Research Act of 1990 Public Law 101 -606(11/16/90) 104 Stat. 3096 -3104 "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.

Change in atmospheric composition Climate change Nitrogen deposition Change in stratospheric ozone Tropospheric ozone pollution. . . Atmospheric CO 2 enrichment

Land use change and anthropogenic disturbance

Alien species invasion A. Danin Barry A. Rice

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

Differential impact of global change on plant species Global change manipulation in a ‘natural’ grassland in California: • Atmospheric CO 2 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. 2003 Ecol. Monogr.

Aboveground biomass (g m-2) Change in aboveground biomass (g·m-2) Impact of global change on plant species: example from a semi-arid community under atmospheric CO 2 enrichment 25 20 Onobrychis crista-galli P = 0. 009 440 -280 15 300 a b b 200 100 0 280 440 600 CO 2 concentration (ppm) 600 -280 10 A. s. 5 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. 0 H. s. -5 H. c. M. t. T. c. S. c. H. u. R. s. D. g. R. p. Br. d. P. cr. Species Grünzweig & Körner. 2001. Oecologia. Grünzweig & Körner. 2001. Oikos R. a. S. p.

Some growth-determining plant factors that can be altered by elevated CO 2 • 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) LWRa • Allocation of carbon to symbionts and exudation 0. 4 0. 3 0. 2 0. 1 0. 0 280 440 600 CO 2 concentration (ppm) Leaf weight ratio (LWRa = leaf DW / total aboveground DW) for Onobrychis crista-galli

Water saving under atmospheric CO 2 enrichment as indirect effect on plant performance and species composition Low CO 2 High CO 2 Evapotranspiration Rain 28 7 39 7 Soil moisture Water leaching Period during growing season Morgan et al. 2004. Oecologia Onobrychis crista-galli: the largest species and the most mesic legume in the community

Seed production at elevated CO 2 Onobrychis crista-galli Parentucellia flaviflora 600000 Seed production (no. m-2) 1200 P = 0. 010 P = 0. 001 800 400000 400 200000 0 0 280 440 600 CO 2 concentration (ppm) A. Danin

Competition between a semi-arid C 4 pasture grass and an invasive C 3 weed under atmospheric CO 2 enrichment P. h. : C. c. = 1: 1 Cenchrus ciliaris introduced C 4 pasture grass in semiarid subtropical and tropical pastures of northern Australia Parthenium hysterophorus invasive C 3 weed P. h. : C. c. = 1: 3 Potential causes of increased growth and reproduction of P. hysterophorus under elevated CO 2: Plant water savings and accelerated plant development under conditions of rapid soil drying

Invasive weeds under past and future atmospheric CO 2 enrichment Potential causes of increased growth under elevated CO 2: Substantial belowground sinks contributing to largely stimulated plant growth → potential link between invasiveness and CO 2 responsiveness Increase in total biomass (%) Ziska. 2003. J. Exp. Bot.

Hemiparasite performance under global change Phoenix & Press. 2005. Folia Geobot.

Responses of C 3 and C 4 species to global change Atmospheric CO 2 enrichment Higher sensitivity of C 3 vs. C 4 photosynthesis to elevated CO 2 Stimulation of C 4 relative to C 3 species by elevated CO 2 under warm and dry conditions Climate change Global warming: favors C 4 plants in general Timing of global warming: Warmer winters → stimulation of C 3 plants Warmer and wetter summers → stimulation of C 4 plants Warmer and drier summers → suppression of C 4 plants (unless fire plays a role in the ecology of the site)

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

Skinner et al. 2000. Weed Sci.

Enhancement of an invasive annual grass under atmospheric CO 2 enrichment in the desert Success of the invasive alien Bromus madritensis spp. rubens in the Mojave Desert FACE experiment Smith et al. 2000. Science

Positive feedback loops of alien plant invasion Invasive alien cheatgrass (Bromus tectorum) Yield losses and costs for weed control (W USA, Canada): US$ 350 -375 million/year Evans et al. 2001. Ecol. Appl.

Mediterranean islands

Plant invasion on Mediterranean islands Human-dominated habitats Habitat Modified from Hulme et al. 2008 In: Tokarska-Guzik et al. , Backhuys Publishers

Impact of climate and land use on plant invasions Oxalis pes-caprae invasion on the island of Crete (Greece) Initial bulbil biomass Barry A. Rice Agricultural sites colonized by Oxalis pes-caprae Ross et al. 2008 Persp. Plant Ecol. Evol. Syst.

Model output on the effect of disturbance frequency on native and invasive species on the island of Lesbos (Greece) Juniperus oxycedrus Quercus coccifera Quercus ilex Ailanthus altissima Gritti et al. 2006. J. Biogeogr.

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 C 4 herb) Plantago lanceolata (native herb) Different native trees and shrubs Gritti et al. 2006. J. Biogeogr.

Theory of alien invasions can suggest causes for successful invasive weeds a) Increased resource availability b) Enemy release Davis. 2000. J. Ecol. Combination of a) and b) Blumenthal. 2005. Science Invasive species Keane & Crawley. 2002

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

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 C 4 weeds • Higher water use efficiency • Better adapted to elevated temperatures and heat stress than C 3 plants Hemiparasites Effects of host water, carbon and nutrient relations

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 (C 4) for integration and spread • Elevated CO 2 → competitive advantage (species with large seed or belowground sinks) for integration and spread