Impacts of Soil Warming and Plant Rhizosphere on Root Litter Decomposition at Different Soil Depths in a Mediterranuan Grassland Lysimeter Facility
Biao Zhu1, Caitlin Hicks Pries2, Cristina Castanha3, John Bryan Curtis1, Rachel C Porras1 and Margaret S Torn4, (1)Lawrence Berkeley National Laboratory, Berkeley, CA, United States, (2)Dartmouth College, Department of Biological Sciences, Hanover, United States, (3)Lawrence Berkeley National Laboratory, Climate and Ecosystem Sciences Division, Berkeley, United States, (4)Lawrence Berkeley National Laboratory, Climate and Ecosystem Sciences Division, Berkeley, CA, United States
Abstract:
Accurate understanding of soil carbon cycling is critical for predicting climate-ecosystem feedbacks. Decomposition of root litter and its transformation into soil organic matter (SOM) are critical processes of soil carbon cycling. We aim to study the impacts of soil warming and plant rhizosphere on the fate of
13C-labeled roots buried at two soil depths using a field lysimeter facility at Hopland, California. The lysimeters contain soil columns of 38-cm diameter and 48-cm depth (0-15 cm A-horizon, and 15-48 cm B-horizon, Laughlin soil series) sown with annual grasses dominated by
Avena barbata. The experiment has three treatments (planted-ambient, planted-warming (+4°C), and unplanted-ambient). In February 2014,
13C-labeled
A. fatua roots were added to two depths (8-12 and 38-42 cm). We measured root-derived
13C in respired CO
2 collected at the soil surface and in leachate dissolved organic carbon (DOC) collected from the lysimeters during the growing season and in soil harvested in August 2014.
We found (1) soil temperature at two depths (10- and 40-cm) have been elevated by 4±0.2°C in the warmed compared to the ambient lysimeters; (2) surface (10-cm) volumetric soil moisture followed this order (unplanted-ambient > planted-ambient > planted-warming), while subsurface (40-cm) soil moisture showed little variation among treatments; (3) ecosystem respiration was enhanced by soil warming during the early growing season (March 15th and April 5th) when soil moisture was not limiting (>20%), while it was suppressed by soil warming during the late growing season (May 7th) when soil moisture was limiting (<20%), and was not significantly different among treatments towards the end of growing season (May 20th); and (4) aboveground plant biomass increased 25% with soil warming. More data including 13C values of ecosystem respiration, DOC loss, and harvested soil samples, as well as soil nutrient supply rates, microbial biomass and community structure will be presented during the meeting. Overall, these results suggest that the impact of soil warming and plant rhizosphere on ecosystem carbon cycling is dependent on season (or soil moisture level) in this Mediterranean grassland ecosystem.
