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

PurposeThe sensitivity of wildland plants to temperature can be directly measured using experimental manipulations of temperature in situ. We show that soil surface temperature and plant density (per square meter) have a significant impact on the germination, growth, and phenology of Bromus tectorum L., cheatgrass, a short-statured invasive winter-annual grass, and assess a new experimental temperature manipulation method: the application of black and white gravel to warm and cool the soil surface.MethodsWe monitored height, seed production, and phenological responses of cheatgrass, seeded into colored gravel at low and high densities at two sites in the western USA: Boise, ID and Cheyenne, WY. Soil surface temperature and volumetric water content were measured to assess treatment effects on soil surface microclimate.ResultsBlack gravel increased mean temperatures of the surface soil by 1.6 and 2.6 degrees C compared to white gravel in Cheyenne and Boise, respectively, causing 21-24 more days with soil temperatures > 0 degrees C, earlier cheatgrass germination, and up to 2.8-fold increases in cheatgrass height. Higher seeding density of cheatgrass led to 1.4-fold taller plants on black gravel plots at both sites, but not white gravel at the Boise site, indicating a possible thermal benefit or reduction of water demand due to plant clustering in warmer treatments.ConclusionsManipulating 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.

Automated summary

This study demonstrates that soil surface temperature and plant density have a significant impact on the germination, growth, and phenology of cheatgrass. The researchers also assessed a new method of temperature manipulation using black and white gravel.