Effects of global warming on soil organic matter (SOM) dynamics remain a widely debated topic. Some scientists hold the view that climatic warming increase soil temperature and accelerate organic matter decomposition rates, leading to loss of soil C and N. While the other studies have reported that warming leads to increases in soil C and N because of great increases in biomass and litter inputs in tundra ecosystems.

Scientists at Wuhan Botanical Garden (WBG) and the University of Oklahoma have been studying SOM dynamics in a North America tallgrass prairie in an attempt to discover the influence of global warming on terrestrial ecosystems. The scientists combined soil fractionation with isotope analyses to examine SOM dynamics after nine years of experimental warming in a North America tallgrass prairie. Soil samples from the control plots and the warmed plots were separated into four aggregate sizes (>2000 μm, 250–2000 μm, 53–250 μm, and <53 μm), and three density fractions (free light fraction – LF, intra-aggregate particulate organic matter – iPOM, and mineral-associated organic matter – mSOM). All fractions were analyzed for their carbon (C) and nitrogen (N) content, and δ¹³C and δ¹⁵N values.

Their study showed that warming did not significantly affect soil aggregate distribution and stability but increased C4-derived C input into all fractions with the greatest in LF. The δ¹³C analysis showed that warming stimulated decay rate of C in whole soil and all aggregate sizes. C in LF turned over faster than that in iPOM in the warmed soils. The δ¹⁵N analysis showed that warming accelerated the circulation and loss of soil N. The δ¹⁵N values changed from low to high, while C:N ratios changed from high to low in the order LF, iPOM, and mSOM due to increased degree of decomposition and mineral association.

The study entitled “Soil organic matter dynamics in a North America tallgrass prairie after 9 yr of experimental warming” has been published in Biogeosciences, 8:1487-1498. doi:10.5194/bg-8-1487-2011.

Abstract: http://www.biogeosciences.net/8/1487/2011/bg-8-1487-2011.html