Shifts in Microbial Community Composition and Physiological Profi les across a Gradient of Induced Soil Degradation

1327 Soil Sci. Soc. Am. J. 73:1327-1334 doi:10.2136/sssaj2008.0276 Received 20 Aug. 2008. *Corresponding author ([email protected]). © Soil Science Society of America 677 S. Segoe Rd. Madison WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. T eff ects of land use change and agriculture practices on the composition and diversity of soil microbial communities have been demonstrated using both genetic and physiological techniques. Buckley and Schmidt (2001) showed that fi elds sharing a history of cultivation possessed diff erent T-RFLP profi les, and reduced diversity of rRNA genes associated with α-Proteobacteria, β-Proteobacteria, and Actinobacteria compared with uncultivated fi elds. Microbial community structure also diff ered between cultivated and uncultivated soils based on PLFA analysis (Bossio et al., 2005). Soils that were tilled (Lupwayi et al., 1998) or converted from native vegetation to agriculture (Gomez et al., 2000, 2004; Nsabimana et al., 2004) presented diff erent CLPP, and reduced physiological diversity. Despite these well established facts, it remains unclear what delineates a situation where a soil community makes physiological adjustments to environmental disturbance without undergoing community composition change, from one where there is a concomitant community shift (Schimel et al., 2007). Furthermore, it is unknown to what extent a shift in community composition results in greater community resistance to further abuse and buffers against further shift s in composition. In most situations the ability to make this type of association would have been impaired because the responses of microbial communities to treatments might have been infl uenced by non-edaphic factors. For example, Yan et al. (2000) associated the reduced physiological diversity of cultivated vertisols assessed by the CLPP method with reduced soil organic C compared with uncultivated vertisols. However, this diff erence could also be the result of other factors infl uencing soil microbial diversity, such as the history of chemical applications to cultivated fi elds in the form of fertilizer, insecticides, and herbicides, and higher plant diversity in the uncultivated sites. In another study, the evaluation of a grassland restoration Guilherme M. Chaer* Embrapa Agrobiologia BR-465, km 7 Caixa Postal 74505 Seropédica, RJ, Brazil 23890-000