Changes in soil microbial community structure with tillage under long-termwheat-fallow management

Fatty acid methyl esters (FAMEs) were used to 'fingerprint' soil microbial communities that evolved during 25 years of wheat-fallow cropping following native mixed prairie sod at Sidney, Nebraska, USA. Total ester-linked FAME s (EL-FAMEs) and phospholipid-linked FAMEs (PL-FAMEs) were compared for the ir ability to discriminate between plots remaining in sod and those cropped to wheat or left fallow under no-till, sub-till or plow management. Croppe d plots were higher in microbial biomass than their fallowed counterparts, and did not differ significantly with tillage for the 0-15 cm depth. Under fallow, microbial biomass was greatest in no-till and least in plow. Both c luster and discriminant analysis of PL- and EL-FAMEs clearly separated the remaining native sod plots from the existing wheat-fallow plots. This separ ation was particularly pronounced for the EL-FAMEs and was largely driven b y high amounts in sod of a single FAME, C16:1(cis11), which has been cited as a biomarker for arbuscular mycorrhizal (AM) fungi. Within wheat-fallow, C16:1(cis11) declined significantly from no-till to plow, which supports th e origin of C16:1(cis11) from extraradical mycelium and spores of AM fungi known to be sensitive to soil disturbance. Although discriminant analysis o f PL- and EL-FAMEs differentiated wheat and fallow systems by tillage, disc rimination among tillage treatments was expressed most strongly during fall ow. FAME profiles from fallow plow were most dissimilar from cropped soils which suggests a relationship between tillage management and the long-term resiliency of the microbial community developed under the wheat crop. (C) 2 000 Elsevier Science Ltd. All rights reserved.