Ea model ce 1100

¹³C labeled plant foliar litter was produced in glass chambers in the greenhouse by growing Dysphania ambrosioides (formerly Chenopodium ambrosioides), a temperate herb with vermiculite as a substrate. A constant supply of ¹³CO₂ (∼1 atom% ¹³C) at 400 ppm was maintained in continuous flow-through growth chambers. The mesocosms were uniformly watered with an automated irrigation system; and additional light was provided 12 h per day. After 3 months of growth, plants were harvested; leaves were separated, dried at 40°C, shredded and ground in a ball-mill. The product was subsequently sieved (<500 μm) and the finer powder was used for soil application. An aliquot was taken for ¹³C analysis on elemental analyzer coupled to an isotope ratio mass spectrometer (EA model CE 1100 coupled on-line via a Con Flo III[27] interface with a Delta + isotope ratio mass spectrometer; all supplied by Thermo Fisher Scientific, Germany). Fifty milligram of plant leaf litter (2.1 ± 0.1 atom%) was added to each soil mesocosm that was equivalent to 531.3 ± 21.5 μg¹³C.

Before¹³C analysis of bulk soil organic carbon, dried soil was ground using a ball-mill and acidified to remove carbonates. After drying, plant parts were shredded and ground in a ball-mill (Kramer and Gleixner, 2008 (link)). Bulk ¹³C analysis of SOM and plant material was performed on an elemental analyzer coupled to an isotope ratio mass spectrometer (EA model CE 1100 coupled on-line via a Con Flo III[27] interface with a Delta⁺ isotope ratio mass spectrometer; all supplied by Thermo Fisher Scientific, Germany). To measure the plant and soil respired ¹³CO₂, three plant pots were placed into a 2000 L airtight glass chamber in the dark (post sunset) at 1, 2, 4, 7, 14, and 21 days after pulse labeling of plants. The concentration of CO₂ in the chamber and its ¹³C content was continuously monitored for 90 min at each time point using a Picarro 2101i (Picarro Inc., Santa Clara, CA, USA). To estimate the δ¹³C value of total respired CO₂, the reciprocal of CO₂ concentration was plotted against δ¹³C value of chamber CO₂ over the analysis period (Keeling plot), with the y-intercept representing the δ¹³C value of total respired CO₂ (Pataki et al., 2003 (link)).