Submitted to: Ecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2010
Publication Date: 8/1/2010
Publication URL: http://hdl.handle.net/10113/47063
Citation: Aanderud, Z.T., Richards, J.H., Svejcar, A.J., James, J.J. 2010. A shift in seasonal rainfall reduces soil organic carbon storage in a cold desert. Ecosystems. 13:673-682. Interpretive Summary: Some climate models suggest that the distribution of precipitation in the Great Basin may shift in the future. One proposed scenario is slightly less winter and more early summer precipitation. Over a ten-year period we excluded natural precipitation and watered sagebrush/bunchgrass plant communities at different times of the season. If we do see a shift in precipitation timing from dominant winter to dominant spring/summer, there will be a decline in soil organic carbon. The decomposition of soil organic carbon most likely will contribute to atmospheric CO2. Climate modelers can use this information in future climate projections.
Technical Abstract: Shifts in the seasonal timing of precipitation have the potential to substantially reduce the immense terrestrial stores of soil organic C (SOC). It remains unclear, however, how changes in timing are influencing SOC storage or contributing to rising atmospheric CO2. We hypothesized that if the timing of precipitation shifted to coincide with warmer soil temperature, SOC stores may become susceptible to decomposition. To investigate this, we evaluated how an eleven-year seasonal shift in precipitation (winter to spring-summer regime) impacted SOC storage (i.e., dissolved organic C, light SOC, and heavy SOC) in soils beneath dominant shrub and perennial grass species in a cold desert. We also measured SOC C to N ratios and litter C stocks to help determine how shifts in SOC occurred. As hypothesized, when precipitation shifted from winter to spring-summer, heavy SOC declined beneath Artemisia tridentata ssp. wyomingensis by 14% from 3.1 to 2.7 kg C m-2 and Pseudoroegneria spicata by 19% from 3.0 to 2.4 kg C m-2. Neither dissolved organic C nor the light fraction responded to changes in precipitation. The C to N ratio of heavy SOC beneath Artemisia declined by at least 6% under the warmer and moister conditions of the spring-summer, suggesting that alterations in decomposition dynamics contributed to the loss of SOC. However, woody litter and root C in Artemisia soils were lower under spring-summer than winter, suggesting that a decline in litter inputs also contributed to the decline in SOC. The reason for the loss of heavy SOC beneath Pseudoroegneria was less apparent, but there was evidence that SOC was reduced by alterations in decomposition and litter. The C lost from heavy SOC was not recaptured in other SOC stores or litter stocks. Therefore, this reduction most likely contributed to increasing atmosphere CO2 concentrations, further intensifying precipitation change.