COS 226-5 - Event and seasonal responses of soil respiration to environmental variation on the Colorado Plateau

Background/Question/Methods

Because of the prevalent terrestrial landcover, dryland ecosystems are a major regulator of global carbon sequestration. Biological soils crusts (biocrusts) are hypothesized to be key components in promoting increased carbon sequestration into soils. Biocrusts help preserve dryland soils, increase water infiltration, and are essential in nutrient cycling. Biocrust activity is largely impacted by seasonal climatic events, as well as proximity to patches of vegetation. Anthropogenic climate change and land use are expected to decrease biocrust cover, threatening these important services. While other studies have used experimental wetting treatments, none have looked at long-term in situ settings. Understanding biocrust carbon dynamics in a contemporary setting is necessary to understanding how future climate could affect biocrust sink attributes. Our question is how do seasonal climate events and location within a landscape affect biocrust carbon dynamics? To answer this, we installed soil respiration auto-chambers on biocrusts in Moab, UT since 2020 to record hourly CO₂ fluctuations. We applied a spatial treatment by placing chambers in the shrub interspace (bare soil) and beneath blackbrush in a vegetation patch. With the collected CO₂ data, we can observe how biocrusts have responded differently across the landscape and during seasonal variation.

Results/Conclusions

Biocrusts are heavily influenced by the location within a landscape, as biocrust respiration fluctuated less underneath blackbrush in comparison to biocrusts located in the shrub interspace. This largely correlated to better microclimate regulation of temperature and moisture provided by the presence of vegetation. Biocrust CO2 respiration also had significantly increased responses following summer precipitation events, where crusts became carbon sources instead of carbon sinks. We attribute this large release of CO2 to the Birch Effect where a burst of decomposition, respiration, and release of CO₂ occurred from wetting after a prolonged drought has dried the soil and biocrusts. These findings implicate that the location of biocrusts, presence of dryland shrubbery, and shift in dryland climate patterns could all have detrimental consequences to regional and global carbon sequestration. Less frequent summer precipitation accompanied with prolonged droughts could reverse biocrust carbon dynamics. Changes in land use and increasingly arid climate could lead to vegetation loss causing dynamic fluctuations in soil microclimate and biocrust respiration. With a better understanding of biocrust dynamics, land management decisions should be focused on preserving landscape integrity and trying to mitigate shifts in dryland climate.