The role of litter in enhancing water availability to Bromus tectorum L. (cheatgrass) changes according to soils

Authors: MORRA, BRIAN - University Of Nevada; Newingham, Beth; SULLIVAN, BEN - University Of Nevada; ELLIS, JACOB - University Of Nevada; DENCKER, CAMIE - University Of Nevada

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2025
Publication Date: 7/29/2025
Citation: Morra, B., Newingham, B.A., Sullivan, B.W., Ellis, J.C., Dencker, C.M. 2025. The role of litter in enhancing water availability to Bromus tectorum L. (cheatgrass) changes according to soils. Plant and Soil. 2025. https://doi.org/10.1007/s11104-025-07731-w.
DOI: https://doi.org/10.1007/s11104-025-07731-w

Interpretive Summary: The invasive annual grass, Bromus tectorum L. (cheatgrass), is present in most rangelands of the western United States. It has changed fire return intervals and contributes to the roughly 1.2 million acres that burn annually in western rangelands. Therefore, understanding drivers of cheatgrass invasion and growth is critical for limiting the impacts of wildfires. Because many western rangelands are water-limited ecosystems, we examined the effects of litter on soil-water and cheatgrass growth across common soils of the Great Basin. Our work demonstrates that soils play an important role in understanding differences in the establishment of exotic annual grasses in semiarid ecosystems. We show litter management can limit cheatgrass germination and survival to a greater degree in low organic matter soils than high organic matter soils. We also show the importance of measuring water potential as it better explained cheatgrass growth, being a more direct metric of plant-available water than total precipitation or volumetric water content. Our work contributes to understanding variable responses to disturbance and management as soil can be highly variable across small areas.

Technical Abstract: The invasive annual grass, Bromus tectorum L. (cheatgrass), is present in most rangelands of the western United States. Invasion is often attributed to its high productivity, which increases fire frequency presumably due to litter buildup. Litter can contribute to favorable microsites where soil moisture is elevated relative to litter-free locations. The role of litter in creating favorable microsites may differ according to soil properties (e.g. soil organic matter (SOM)), which can also contribute to soil-water storage. We investigated whether litter buildup and differences in SOM facilitated or inhibited B. tectorum by comparing the effects of B. tectorum litter on soil moisture, matric potential, and B. tectorum growth using two soil orders common in semiarid rangelands - Mollisols and Aridisols. In a 90-day greenhouse study, B. tectorum seed emergence increased relative to litter-free controls with increasing litter depths from 1-7 cm in the Aridisol but not the Mollisol. The Aridisol had lower SOM and less plant available water than the Mollisol in the absence of litter. However, with increasing litter depth, water availability increased to a greater degree in the Aridisol than the Mollisol, resulting in similar amounts of plant available water at deep litter depths. Thus, water availability was increased by litter in the Aridisol and SOM in the Mollisol. Therefore, litter reduction may be an effective way to mitigate B. tectorum growth for restoration of areas where litter improves water availability. Alternatively, litter reduction may be less effective in soils with characteristics that promote water availability via organic carbon content. By understanding the effects of litter and soil on water availability in drylands, managers can target appropriate treatments to control B. tectorum and restore rangelands.