Climate change, snow mold and the Bromus tectorum invasion: mixed evidence for release from cold weather pathogens

Abstract

Climate change is reducing the depth and duration of winter snowpack, leading to dramatic changes in the soil environment with potentially important ecological consequences. Previous experiments in the Intermountain West of North America indicated that loss of snowpack increases survival and population growth rates of the invasive annual grass Bromus tectorum; however, the underlying mechanism is unknown. We hypothesized that reduced snowpack might promote B. tectorum population growth by decreasing damage from snow molds, a group of subnivean fungal pathogens. To test this hypothesis, we conducted greenhouse and field experiments to investigate the interaction between early snowmelt and either fungicide addition or snow mold infection of B. tectorum. The greenhouse experiment confirmed that the snow mold Microdochium nivale can cause mortality of B. tectorum seedlings. In the field experiment, early snowmelt and fungicide application both increased B. tectorum survival, but their effects did not interact, and snow mold inoculation had no effect on survival. We did find interactive effects of snowmelt and fungal treatments on B. tectorum seed production: with ambient snowpack, M. nivale inoculation reduced seed production and fungicide increased it, whereas in the early snowmelt treatment seed production was high regardless of fungal treatment. However, treatment effects on seed production did not translate directly to overall population growth, which did not respond to the snow melt by fungal treatment interaction. Based on our mixed results, the hypothesis that reduced snowpack may increase B. tectorum fitness by limiting the effects of plant pathogens deserves further investigation.

The impact of climate change on disease in wild plant populations and communities

“…It has been suggested that diminished snowpack formation may favour the population growth and expansion of B. tectorum by reducing the challenge from the snow mould. Among other experimental treatments, early snowmelt increased B. tectorum survival in the field but inoculation with M. nivale had no effect on survival (Smull et al, 2019). With ambient snowpack M. nivale reduced seed production, but with an early snowmelt treatment seed production was not affected.…”

Interannual climate variability has predominant effects on seedling survival in a temperate forest

“…In temperate regions, the transition from winter to spring is becoming increasingly unpredictable because of warming winter temperatures, leading to “false springs,” which will weaken the cold hardiness for woody plants (Augspurger, 2013). Additionally, elevated temperatures reduce the depth and duration of non‐growing season snowpacks (Stewart, 2009), making vegetation experience wider temperature fluctuations, greater exposure to herbivores, more frequent freeze–thaw cycles, and freezing to greater depths (Augspurger, 2013; Smull et al, 2019), potentially reducing the ability to grow and tolerate stem removal in the following growing season (Pescador et al, 2018). Specifically, we found soil and topographic variables had the least explainability for seedling survival.…”

Quantifying the relationship between soil seed bank and plant community assemblage in sites harboring the threatened Ivesia webberi in the western Great Basin Desert

“…Warmer winter temperatures result in rapid snowmelt and increasing soil moisture which support regeneration of winter annuals, such as the invasive Bromus tectorum . Furthermore, reduced snowpack decimates the population of the snow molds which damage Bromus tectorum seedlings (Smull et al, 2019).…”

“…Permutation test for the redundancy analysis of the effects of the predictor variables on the plant community structure in the 10 Ivesia webberi sites. F and p distributions were generated using 10,000 permutations (Smull et al, 2019).…”