Cheatgrass Stand Failure in the Great Basin: Fungal Pathogens, Carbon Dynamics, and Fungistasis

Project Overview

This project proposes to test the hypothesis that soil fungistasis (suppression of fungal pathogens by soil microbes in carbohydrate-limited soil) and its alleviation through natural carbohydrate augmentation (e.g., cheatgrass litter, leakage from cheatgrass roots) are the principal processes mediating patterns of cheatgrass die-off and recovery in die-off-prone areas.

The project team will use laboratory, greenhouse, and field manipulative experiments to examine the effect of soil carbohydrates on cheatgrass disease incidence.

One Year Project Update

The team is testing the hypothesis that cheatgrass die-offs occur when pathogens are temporarily released from fungistasis by a flush of carbohydrate carbon. Fungistasis is again imposed as the soil microbial community rapidly consumes these carbohydrates. Using ring microcosms containing seed bed cores from die-off areas, the researchers have demonstrated that carbohydrate carbon addition can release fungal pathogens from fungistasis and cause epidemic disease that results in near-complete stand failure in the laboratory.

Team members made good progress over the summer in developing PCR protocols for quantifying field inoculum levels for the major pathogens involved in cheatgrass die-off. Researchers continue to monitor their long-term plots in Skull Valley, Utah to follow patterns of die-off and recovery through time.

This year there were sparse but mostly healthy stands of cheatgrass on the plots. Last year a majority of plants failed to set seed and exhibited signs of yellow patch disease caused by Epicoccum nigrum. The low stand density could be a result of both reduced seed production the previous year and possibly some pre-emergence mortality due to this organism, whose role in die-offs is still poorly understood.

This fall the team installed small plot experiments at four recent die-off sites to determine the effect of carbohydrate carbon addition in the field. These experiments will be evaluated in terms of cheatgrass emergence, survival, and seed production. The researchers will use bait seeds planted into the plots to isolate and identify the pathogens involved.

Photograph of cheatgrass die-off

Cheatgrass stand failure or ‘die-off’ is evident as bare patches, often separated by a sharp boundary from areas where cheatgrass successfully produced seeds.

Project Documents

Theme: Disturbance and Development, Plants, Soil and Site Stability

Project start date: 1/1/2015

Fiscal year funded: 2014

Project status: Active

Project managers: Dr. Susan Meyer, USFS Rocky Mountain Research Station