Soil microbial eco-physiological response to nutrient enrichment in a sub-tropical wetland R. Corstanje a, * , K.R. Reddy a , J.P. Prenger a , S. Newman b , A.V. Ogram a a Soil and Water Science Department, University of Florida, Institute of Food and Agricultural Sciences, 106 Newell Hall, P.O. Box 110510, Gainesville, FL 32611-0510, United States b Everglades Department, South Florida Water Management District, P.O. Box 24680, West Palm Beach, FL 33416-4680, United States Received 17 November 2005; received in revised form 8 February 2006; accepted 14 February 2006 Abstract Eutrophication in subtropical wetland ecosystems can lead to extensive displacements of vegetative communities and as a result changes in overall environmental conditions (loss of indigenous habitat, substrate quality, etc.). This has generated a demand for a set of sensitive indicator(s) that prelude these structural changes. The functional response of bacterial communities may indicate the effect and extent of the impact on the overall system. The effects of nutrient enrichment on the microbial community and its ecophysiology were measured in a subtropical marsh (Water Conservation Area 2a) in the northern Everglades, USA. We investigated the microbially mediated organic matter decomposition processes and nutrient cycling in three areas of the marsh, a nutrient enriched site, an intermediate site and a unimpacted (oligotrophic) site. We chose measures associated to the hydrolytic enzyme activities of alkaline phosphatase, b-glucosidase and aminopeptidase. We also monitored microbial biomass carbon (C), nitrogen (N) and phosphorus (P) and the associated elemental turnover rates (C, N and P). We found a significant (a = 0.05) spike in microbial biomass C, N, and P in the intermediate site. The elemental turnover rates (C, N and P) where significantly higher in the impacted and intermediate site when compared to the unimpacted site. The enzymatic profiles at the unimpacted site illustrate a system regulated for optimal use of P. In the intermediate zone between the overall P- limited and P-impacted areas, the nutrient inputs alleviates the stress imposed by the P-limitation. Microbial biomass increased dramatically without a decrease in the overall microbial metabolic efficiency. The metabolic coefficients (particularly q- Potentially Mineralizable P – qPMP and qCO 2 ) indicated that after the disturbance, the impacted areas in the Everglades are characterized by relatively open, inefficient nutrient cycles. The nonlinear shifts (threshold behavior) in microbial parameters indicate that microbial indicators function effectively as early warning signals. # 2006 Elsevier Ltd. All rights reserved. Keywords: Cattail; Ecosystem responses; Eutrofication; Everglades; Microbial activities; Microbial ecophysiological indicators; Nutrient enrichment; Sawgrass; Water Conservation Area 2a This article is also available online at: www.elsevier.com/locate/ecolind Ecological Indicators 7 (2007) 277–289 * Corresponding author at: Biomathematics and Bioinformatics Division, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, United Kingdom. Tel.: +44 1582 763133x2402; fax: +44 1582 760981. E-mail address: Ron.Corstanje@bbsrc.ac.uk (R. Corstanje). 1470-160X/$ – see front matter # 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecolind.2006.02.002