Abstract: To explore the effects of corn straw return on functional diversity of soil microbial community, we investigated carbon metabolic characteristics of soil microorganisms by ECO-Biolog method, under four straw return rates including 6000 kg·hm^-2 (S1), 9000 kg·hm^-2 (S2), 12000 kg·hm^-2 (S3) and 15000 kg·hm^-2 (S4), with no straw return as control (CK). Theresults showed that the average well color development (AWCD) of soil microorganisms increasedwith the increasing rates of corn straw return, AWCD changed rapidly from 24 h to 96 h, and remained relatively stable after 96 h. The AWCD value of S4 treatment was higher than that in other treatments. There were no significant differences for both Shannon index and Simpson index after straw returning (P>0.05), but McIntosh index under S4 treatment was 57.5% higher compared with CK (P<0.05). Results of principal component analysis showed that straw returning affected carbon metabolism capability of soil microbial community, with significant difference among S1, CK, S2 and S3 treatments being found on the PC1 and PC2. Sugars, polymers and carboxylic acids were the main carbon sources used by soil microbes. Therefore, increasing the amount of corn straw returned to the field in the black soil area of Northeast China can improve the utilization capacity of soil microorganisms to carbon sources and improve soil fertility.

Key words: corn straw returning, ECO-Biolog, McIntosh index, carbon metabolic characteristics of soil microorganisms.