Impacts of soil warming and plant roots on organic matter decomposition in a Mediterranean grassland
Accurate understanding of soil carbon cycling is critical for predicting future climate. Decomposition of root litter and its transformation into soil organic matter are critical processes of soil carbon cycling. Thanks to support from the U.S. Department of Energy's Terrestrial Ecosystem Science program, a team led by Dr. Margaret Torn from Lawrence Berkeley National Laboratory have been studying the impacts of soil warming and plant rhizosphere on decomposition of 13C-labeled roots buried at two soil depths using a field lysimeter facility at Hopland Research and Extension Center, California.
The lysimeters contain soil columns of 38-cm diameter and 48-cm depth and annual grasses dominated by wild oats (Avena barbata). The experiment has three treatments (planted-ambient, planted-warming by 4°C, and unplanted-ambient). 13C-labeled Avena fatua roots were added to two depths (8-12 and 38-42 cm). The team will quantify the fate of added root litter in CO2 efflux from soil surface, dissolved organic carbon (DOC) leached from the bottom drain, and organic carbon remaining in bulk soil and different physical fractions for two growing seasons.
First season results show strong role of soil moisture in controlling soil carbon cycling in this Mediterranean ecosystem. Soil warming enhanced plant growth and ecosystem respiration in the early growing season with high soil moisture, while it suppressed plant growth and ecosystem respiration in the late growing season when soil moisture was limited. The team will continue measurements on CO2 flux, DOC loss, and organic carbon recovery in soil fractions, as well as collaborate with microbial ecologists and ecosystem modelers to better understand the underlying processes and to improve the models used for prediction of our future climate.