Dynamics and distribution of 13C-labeled straw carbon by microorganisms as affected by soil fertility levels in the Black Soil region of Northeast China

Microorganisms mediate the decomposition of straw residue in soil, but how soil fertility levels affect microbial incorporation of straw C remains unclear in many ecosystems. The objectives of this study were to quantify the contribution of straw C to microbial organic C (MBC), and to evaluate the effect of different soil fertility levels on the distribution of straw-derived soil organic C (SOC) pools. An in situ incubation was set up with soils amended with or without C-13-labeled maize straw. Across fertility treatments, straw C retained in soil decreased, on average, from 84 % after 30 days (June 5, 2011) to 30 % after 365 days (May 5, 2012). Over the entire incubation, 2-5 % of straw C was incorporated to MBC. At the high and medium fertility levels, MBC contained, on average, 58 % of straw C and 42 % of native SOC, respectively, whereas more than 75 % of MBC was derived from straw C at the low fertility level. Total MBC was lower in soil at the low fertility level compared with soils at the high and medium fertility levels. These results suggest that in low fertility soils, the addition of crop straw significantly promoted the activity and growth of soil microorganisms and provided a potential positive feedback to soil fertility.