Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 27, 2013
Publication Date: June 15, 2013
Citation: Blank, R.R., Morgan, T.A. 2013. Soil engineering facilitates Downy brome (Bromus tectorum L.) growth - A case study. Invasive Plant Science and Management. 6:391-400. Interpretive Summary: We investigated if the exotic invasive grass, cheatgrass, can alter the soil to increase its growth potential. Cheatgrass was grown in soil invaded for 12 years by cheatgrass and in a similar soil not yet invaded. Cheatgrass grown in invaded soil had 250% greater above-ground biomass relative to cheatgrass grown in non-invaded soil. The mechanistic underpinnings involved are inconclusive, but may involve increased availability of soil N, P, and Mn upon long-term occupation by cheatgrass.
Technical Abstract: Some exotic plants are able to engineer new host soils and engender characteristics that potentially increase their growth. We hypothesized that this positive feedback may be a facet in the competitiveness of the exotic annual grass downy brome. Using rhizotrons in the greenhouse, we compared the growth and plant/soil relationships of downy brome grown in two field soil types: invaded for 12 years by downy brome and a similar soil not yet invaded. Original invaded soil had higher levels of mineral N, bicarbonate-extractable P, DTPA-extractable Mn, and solution ortho-P and SO4-2 than non-invaded soil. For each soil type, downy brome was grown for two growth cycles. At harvest, root mass and soil were sampled at depths of 10, 40, and 80 cm, as well as, above-ground biomass. After the 1st growth cycle, downy brome grown in invaded soil had 250% greater above-ground biomass and nearly double root mass per soil volume at 10 cm relative to downy brome grown in non-invaded soil; root mass per volume was statistically similar at depths of 40 and 80 cm. For the 2nd growth cycle, above-ground biomass declined, but was twice greater for downy brome grown in invaded soil; however, root mass per volume was statistically similar between soil types for each depth. Downy brome tissue grown in invaded soil had statistically greater concentrations of N (both growth cycles), and Ca (2nd growth cycle), and statistically less Mn and C:N ratios (both growth cycles) and P (1st growth cycle), and (Zn (2nd growth cycle), than tissue from downy brome grown in non-invaded soil. Soil attributes that positively related to above-ground biomass included bicarbonate-extractable P, DTPA-extractable Mn, solution ortho-P (40 cm depth), and solution SO4-2 (80 cm depth). Following harvest, soil nutrient pools changed relative to original soil: the bicarbonate-P pool declined 33 and 48% and the DTPA Mn pool increased 20 and 56%, respectively for invaded and non-invaded soils. Moreover, the molar proportion of NH4+-N in the mineral N pool averaged 53% for invaded soil and nearly 90% for non-invaded soil, which is opposite to what occurred in the original soil. These data support the hypothesis that downy brome has engineered the soil to increase its growth potential. Plant competition is affected by myriad interactions; however, a plant that can increase the availability of soil nutrients for itself and increase its growth potential, relative to competing plants, would appear to be advantageous. The mechanistic underpinnings involved are inconclusive, but may involve increased availability of soil N, P, and Mn.