Experimental manipulation of soil-surface albedo alters phenology and growth of Bromus tectorum (cheatgrass)

Authors: MAXELL, TOBY - Boise State University; GEMINO, MATHEW - Us Geological Survey; Romero, Seth; Porensky, Lauren; Blumenthal, Dana; BROWN, CYNTHIA - Colorado State University; ADLER, PETER - Utah State University

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2023
Publication Date: 2/28/2023
Citation: Maxell, T., Gemino, M.J., Romero, S.J., Porensky, L.M., Blumenthal, D.M., Brown, C., Adler, P. 2023. Experimental manipulation of soil-surface albedo alters phenology and growth of Bromus tectorum (cheatgrass). Plant and Soil. 487:325-339. https://doi.org/10.1007/s11104-023-05929-4.
DOI: https://doi.org/10.1007/s11104-023-05929-4

Interpretive Summary: To improve knowledge of ecosystem responses to warming temperatures, we need methods that balance cost, feasibility, realism and control. We tested an efficient method for passively warming soils using black or white gravel to modify soil-surface albedo (reflectance), and report responses of cheatgrass, a problematic invasive species in the western USA. We seeded cheatgrass into the gravel at low and high densities, at two sites in the western USA: Boise, ID and Cheyenne, WY. Black gravel increased mean temperatures of the surface soil by 2.9 and 4.7 degrees Fahrenheit compared to white gravel in Cheyenne and Boise, respectively, causing 20-31 more days with soil temperatures > 32 degrees Fahrenheit, increasing cheatgrass germination and height. These results suggest that manipulating soil surface albedo can be an effective, affordable method for research into how warming will influence arid and semiarid ecosystems.

Technical Abstract: Purpose: The sensitivity of wildland plants to temperature can be most clearly known from experimental manipulations of temperature in situ. Methods that balance cost, feasibility, realism and control, and feedbacks of subject vegetation on temperature treatments are needed. However, these multi-faceted aspects of warming treatments are rarely considered. Methods: We present an efficient method for passively warming soils using black or white gravel to modify soil-surface albedo, and report responses of a winter-annual grass that is low-statured, exotic, and invasive (Bromus tectorum L.; cheatgrass) seeded into the gravel at low and high densities, at two sites in the western USA: Boise, ID and Cheyenne, WY. Results: Black gravel increased mean temperatures of the surface soil by 1.6 and 2.6 'C compared to white gravel in Cheyenne and Boise, respectively, causing 20-31 more days with soil temperatures >0 'C (i.e. growing degree days), earlier cheatgrass germination, and up to 2.8-fold increases in cheatgrass height. However, seed production was 2.5-2.9-fold greater on white gravel. Higher seeding density of cheatgrass led to 1.4-fold taller plants on black gravel plots at both sites, but not white at the Boise site, indicating a possible thermal benefit of plant clustering in warmer treatments. Conclusions: Manipulating soil-surface albedo altered the soil microclimate and thus growth and phenology of cheatgrass, whose life history and growth form confer a strong dependency on soil-surface conditions.