GRASSES AS INVASIVE SPECIES

California Valley and Foothill Grassland Ecosystem…GONE!

The California Valley and Foothill Grassland Ecosystem historically resembled PNW perennial bunchgrass ecosystems. Then: Dominated by Stipa pulchra; S. cernua, Danthonia californica, Festuca californica, Sitanion jubatum, Elymus glaucus, Melica californica, etc. California native grasslands have been displaced almost completely by invasive annual grasses via: 1) introduction of Mediterranean annual grasses and forbs (Bromus, Hordeum, Avena, Vulpia, Briza…..); 2) overgrazing; 3) drought, and 4) severe wildfire. Now: a human-mediated disturbance climax vegetation (“disclimax”) that’s permanent, incapable of returning to previous climax vegetation of perennial bunchgrass otherwise expected for the climate and soils of the region.

INVASIVE SPECIES COMPROMISE ECOSYSTEM HEALTH AND INTEGRITY Altered Key Ecosystem Processes and Services include:

• nutrient cycling and carbon cycling [Scot’s broom; Aegilops triuncialis (Drenovsky and Batten 2007)] • sediment erosion and deposition rates (spartina) • disturbance intensities and frequencies (cheat; medusahead)

• evapotranspiration, water cycling, hydroperiods (reed canarygrass ) • soil chemistry and soil biological processes (Holcus ; Russian knapweed) • habitat availability for native plants/animals/other organisms (RCG; quackgrass) • primary productivity (ryegrass)

• genetic integrity (bromes; wheatgrasses; hawkweeds) • resilience to disturbance (incl. biological invasions) (Scot broom)

• biodiversity and asssociated food web interactions/characteristics (spotted knapweed; cheat; RCG)

WHAT IS IT ABOUT GRASSES THAT MAKES THEM SO POTENTIALLY INVASIVE? Versatile morphological body plan combined with reduced floral and fruit structures has allowed an extraordinary capacity for vegetative growth (tillers, stolons, rhizomes, bulbils, corms, fibrous root systems) Intercalary meristems and rapid growth

Apical Meristems (Primary Growth)

Intercalary Meristems

Vascular Meristems (Cambia) (Secondary Growth)

Sclerified and Lignified Vascular Bundle Sheaths (No Secondary Growth)

WHAT IS IT ABOUT GRASSES THAT MAKES THEM SO POTENTIALLY INVASIVE? Versatile morphological body plan combined with reduced floral and fruit structures has allowed an extraordinary capacity for vegetative growth (tillers, stolons, rhizomes, bulbils, corms, fibrous root systems) Intercalary meristems and rapid growth C4 photosynthetic apparatus

Photosynthesis CO2

sunlight, water RuBisCO

Light reactions

Dark reacti ons (Calvin cycle)

Oxygen (O2)

Glucose (C6H12O6) (carbohydrates)

Oxygen causes a problem for RuBisCO • Ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) is a Calvin cycle enzyme that catalyzes the first major step of carbon fixation

• RuBisCO binds O2 as well as CO2; each competes for the active site on RuBisCO • O2 results in no new sugar and deconstruction of photosynthetic products

• Some plants have evolved a way to avoid this wasteful reaction

TWO TYPES OF GRASS PHOTOSYNTHETIC APPARATUS

C3: mesophyll is loosely packed; bundle sheath cells lack chloroplast.

C4: mesophyll is tightly packed and radiately arranged; bundle sheath cells with chloroplasts. PEP shuttles CO2 from mesophyll to bundle sheath cells where it’s concentrated.

TWO TYPES OF GRASS PHOTOSYNTHETIC APPARATUS

C3: Works well < 30 C, but not optimally above this temperature; C3 grasses that keep stomata closed in dry sunny sites undergo high amounts of photorespiration

C4: Works well at temps > 30° C, but not optimally < 30° C; advantageous in dry warm climates or open sunny sites because they can keep leaf stomata closed during mid-day and extract every last CO2 molecule in the leaf. C4 plants typical of hot, tropical environments with high light. Advantages of C4: 1) avoids photorespiratory loss of carbon (oxidation of photosynthetic products); 2) improves water use efficiency; 3) results in higher rates of photosynthesis at high temperatures; 4) improves efficiency of nitrogen use (because C3 require lots of RuBisCO).

WHAT IS IT ABOUT GRASSES THAT MAKES THEM SO POTENTIALLY INVASIVE? Versatile morphological body plan combined with reduced floral and fruit structures has allowed an extraordinary capacity for vegetative growth (tillers, stolons, rhizomes, bulbils, corms, fibrous root systems) Intercalary meristems and rapid growth

C4 photosynthetic apparatus Inherent developmental plasticity (drought, cold, grazing, fire, climate change…) Pre-adapted genotypes (11,000 species World-wide!) Rapid evolutionary capacity (post-immigration evolution and microevolution) [Novack and Mack (2005): founder effects but high intra-population diversity from multiple introductions and novel genotypes; Longland and Ashleu 2007: evidence for local adaptation]

WHAT IS IT ABOUT GRASSES THAT MAKES THEM SO POTENTIALLY INVASIVE?

Allelochemicals [Hogal and Sanford (2006) report Bromus tectorum root extracts reduced growth of Hilaria jamesia by 60%; Lolium and Pinus ponderosa] Escape from biotic constraints Prolific seed production

Heliophytes and disturbance-response species Extended seed dormancy…..

Bromus, Lolium, Vulpia in California

Brachypodium in California