PS 40-107 - CANCELLED - Precipitation variability effects on dryland carbon sequestration depend on resource availability

Abstract: Drylands represent an import carbon (C) sink in the Earth System. In these systems, climate change is projected to not only affect precipitation amount but also to increase its interannual variability, with more extreme dry and wet events. Additionally, nitrogen (N) deposition is increasing across many drylands in western North America, which may alter rates of C sequestration. To project future feedbacks on C cycling, it is important to understand how changes in interannual precipitation variability and N deposition influence ecosystem C dynamics. While many studies have examined how individual events (e.g., droughts) influence vegetation growth, little attention has been paid to the cumulative effect of drought on plant growth over multiple decades. To address this gap, we applied an ecohydrological model in two semiarid watersheds in the western US, one with mixed vegetation cover, including evergreen trees, shrubs, and grasses and the other dominated by chaparral. We conducted a series of sensitivity analyses to investigate how variation in N deposition and interannual precipitation variability (measured by a coefficient of variation) influence vegetation growth and C sequestration. We found that higher interannual precipitation variability can enhance vegetation growth, but this depends on resource availability such as N and water. In a N-limited system, higher interannual precipitation variability can increase C accumulation due to increases in N availability after drought. However, in an N-saturated system, higher interannual variability can reduce C accumulation because N accumulation during drought does not play as much of a role in vegetation growth. Additionally, we found vegetation response to interannual variability changes along a soil moisture gradient. Higher precipitation variability can promote vegetation growth in dry regions but not in wet ones. Our research provided insights into how local N pollution and soil moisture gradients will influence C sequestration in drylands under climate change.