Cheatgrass Soil Engineering/Perennial Grass Suppression of Cheatgrass: The Yin and Yang of Plant Competition in Northern Nevada

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1 Cheatgrass Soil Engineering/Perennial Grass Suppression of Cheatgrass: The Yin and Yang of Plant Competition in Northern Nevada Cheatgrass modifies soil to favor its growth Established perennial grasses suppress the growth of cheatgrass

2 Cheatgrass Soil Engineering A Case Study In 1998, cheatgrass began invasion of a winterfat community in the Honey Lake Valley. In 1 years, the winterfat site had largely converted to cheatgrass dominance. Why? The soil is very infertile and loamy sand in texture.

3 Soil Engineering or Conditioning: The plant-induced modification of soil chemical, biological, and physical characteristics, whereby growth of the plant is facilitated. Cheatgrass soil engineering makes nutrients more available than engineering by native vegetation. Mineral N (mmol kg -1 ) Sene scent Grow ing Cheatgrass Native Solution-phase phosphorus (µmol L -1 ) Shoshones Col um bi a Hill Eden Valley Izzenhood Keys tone Ca nyon Cheatgrass Native Re d Roc k Hone y L ake

4 Soil Engineering by Cheatgrass Soil modified by cheatgrass invasion is a better medium for growth of cheatgrass than soil conditioned by native vegetation. Aboveground plant biomass over 3 times greater. Over 2 times greater root biomass at 1 cm, but similar root biomass at 4 and 8 cm. Significantly greater tissue N. Soil from area invaded by cheatgrass for 1 years. Soil from adjacent area not yet invaded by cheatgrass.

5 How Does Cheatgrass Engineer the Soil? Cheatgrass roots exude carbon into soil. Alters soil microbial community more fungal dominated and greater microbial biomass. Greater enzyme activities of amidohydrolases and phosphatases.

6 Perennial Grass Suppression of Cheatgrass Definition: Reduction in plant above-ground growth, root proliferation, plant vigor, reproductive ability, due to the presence of a competing plant. Established perennial grasses suppress cheatgrass.

7 Perennial Grass Suppression of Cheatgrass Above-ground mass (g) Above-ground mass (g) Sna ke Ri ve r w he atgra ss Cre epi ng w ildrye Indi an ri cegra ss No fertilizer + fertilizer Che atgra ss % Sna ke Ri ve r w he atgra ss Cheatgrass planted between established perennial grass. 99.8% 99.8% 99.5% Cre epi ng w ildrye 97.7% 95.1% Indi an ri cegra ss

8 Perennial Grass Suppression of Cheatgrass Cheatgrass planted 5, 35, and 7 cm from established crested wheatgrass and allowed to grow for 7 days. Experiment 1 crested wheatgrass established for 9. Experiment 2 crested wheatgrass established for 1 year. Cheatgrass AGM (g) Crested wheatgrass 9 days Cheatgrass AGM (g) Crested wheatgrass 1 year 5 cm 35 cm 7 cm Distance from crested wheatgrass

9 How do Perennial Grasses Suppress Cheatgrass? Soil Nitrogen Availability Cheatgrass grown in competition with established perennial grasses have less tissue N. Strong relationships between soil N availability and cheatgrass biomass. 6 Crested wheatgrass 9 days Cheatgrass N (%) Crested wheatgrass 1 year Cheatgrass N (%) cm 35 cm 7 cm Distance from crested wheatgrass

10 How do Perennial Grasses Suppress Cheatgrass? Controlling the dominant form of mineral N? 1 NH 4 + in mineral N (mole %) Date Crested wheatgrass Shrub Interspace In a long-established crested wheatgrass planting, that effectively suppresses cheatgrass, the dominant form of mineral N was in the NH 4+ - N form Cheatgrass prefers NO 3- -N As soil dries, transport of NH 4+ -N to plant root very slow

11 Controlling the dominant form of mineral N Mole NH 4 + (%) Crested wheatgrass 9 days Mole NH 4 + (%) Crested wheatgrass 1 year In our greenhouse study, the longer perennial grass established, the greater molar proportion of NH 4+ -N 5 cm 35 cm 7 cm Distance from crested wheatgrass Do perennial grasses retard nitrification?

12 How do Perennial Grasses Suppress Cheatgrass? Allelopathy/Biological Soil Space Suppressed cheatgrass is characterized by lack of lateral rooting and poorly developed root hairs. 2(3H)-benzoxazolinone exuded from ryegrass inhibits lateral root formation. Cheatgrass roots simply cannot enter soil space occupied by roots of crested wheatgrass.

13 What Does it all Mean? Cheatgrass has greater potential range of expansion due to ability to engineer soil. Potential to select perennial grasses for suppressive ability.

14 Questions?