A32E-05
Observed Global Historical Changes in Soil Decomposition Rates (1900–2011) and Plant Production (1981–2011)
Wednesday, 16 December 2015: 11:20
3006 (Moscone West)
William J Parton1, William K Smith2, Justin D Derner3, Steve Del Grosso4, Maosi Chen1 and Whendee L Silver5, (1)Colorado State Univ, Fort Collins, CO, United States, (2)University of Minnesota Twin Cities, Institute on the Environment, Minneapolis, MN, United States, (3)USDA ARS, Northern Plains Regional Climate Hub, Cheyenne, WY, United States, (4)USDA ARS, Fort Collins, CO, United States, (5)University of California Berkeley, Dept of Environmental Science, Policy, & Management, Berkeley, CA, United States
Abstract:
This paper presents a unique analysis of changes in global soil decomposition rates from 1900 to 2011, determine which climatic factors have caused the observed historical changes in soil decay rates, and compares changes in soil decay rates with observed changes in plant production from 1981 to 2011. This analysis allows us to determine the impact of climatic changes from 1981 to 2011 on soil carbon (C) sequestration. We use observed global monthly global Climatic Research Unit (CRU) weather data from 1900 to 2011 (0.5° x 0.5° spatial scale) to calculate annual changes in the climatic decomposition index (CDI), an analog for soil decay rates. The CRU data was also used to calculate annual changes in precipitation, mean annual temperature, potential evapotranspiration and actual evapotranspiration (AET) rates at the 0.5° x 0.5° spatial scale. Annual changes in plant production (NPP) at the global scale were calculated using global satellite derived Normalized Difference Vegetation Index (NDVI) data sets. At the global scale CDI showed little change from 1900 to 1980 but increased by 4% from 1980 to 2011. CDI increased by more than 10% in tundra and boreal forest systems from 1980 to 2011 (< 4% for all other biomes). Changes in CDI are well correlated to changes in AET rates (r2 > 0.8) with a 2 to 4% increase in AET for most biomes (no change for dry grassland and desert biomes). NPP increased by > 6% for tundra, boreal forest and temperate forest from 1980 to 2011 with latitudinal average changes in NPP and CDI following similar patterns (greatest increases in the +40° to +75° latitudes). Global patterns in NPP are well correlated to AET and CDI (r2 > 0.8) but have different patterns (linear for AET and curvilinear for CDI). Latitudinal averaged ratio of NPP:CDI is correlated to Harmonized World Soil Database soil C levels (r = 0.67). Statistically significant trends (1980–2011) in NPP:CDI suggest increases in soil C for the boreal forest and temperate dry grassland and decreases in soil C for humid tropical forests (no trends for other biomes) from 1980 to 2010. Statistical analysis of the observed increases in NPP and CDI for the northern latitudes is most correlated to observed increases in air temperature.
