The respiration of flocculent detrital organic matter (floc) is driven by phosphorus limitation and substrate quality in a subtropical wetland Oliva Pisani a,c, ⁎, Leonard J. Scinto b,c , Jay W. Munyon d , Rudolf Jaffé a,c a Department of Chemistry & Biochemistry, Florida International University, Miami, FL 33199, USA b Department of Earth & Environment, Florida International University, Miami, FL 33199, USA c Southeast Environmental Research Center, Florida International University, Miami, FL 33199, USA d Department of Biological Sciences, Florida International University, Miami, FL 33199, USA abstract article info Article history: Received 5 February 2014 Received in revised form 20 November 2014 Accepted 25 November 2014 Available online xxxx Keywords: Floc Everglades Respiration Phosphorus limitation Carbon quality The aerobic respiration of flocculent detrital organic material (floc) from Everglades National Park was found to be dependent on phosphorus limitation and carbon quality and is likely influenced by substrate age, hydrology, and local biomass productivity. Floc was collected at four sites along the Shark River and Taylor Sloughs of Ever- glades National Park and incubated for up to one week at room temperature in the dark. Floc respiration was de- termined by measuring the total amount of CO 2 evolved and CO 2 generation rates. To investigate the effect of hydrological conditions, samples were collected in a typical dry (April) and wet (October) season and from short- and long-hydroperiod sites. Floc from the short-hydroperiod freshwater site generated more CO 2 com- pared to the long-hydroperiod site due to the labile nature of the periphyton-derived organic matter at the for- mer and the presence of more degraded and aged material at the latter. The tidally-influenced Shark River Slough mangrove site generated more CO 2 compared to the Taylor Slough mangrove site, likely as a result of phosphorus inputs from the adjacent Gulf of Mexico at the former and reduced phosphorus inputs and prolonged inundation at the latter. Generally, more CO 2 was generated during the dry season. Floc respiration rates were faster in the wet season, suggesting that fresh vegetation inputs to the floc can influence this process. Phosphorus and glucose additions enhanced CO 2 generation suggesting that phosphorus limitation and carbon quality are important fac- tors regulating floc decomposition. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The cycling of organic carbon (OC) in wetlands has been widely studied due to the complexity of carbon dynamics in these environ- ments and its critical role in the global carbon cycle (Bridgham et al., 2006; DeBusk and Reddy, 2005; Kayranli et al., 2010; Neue et al., 1997). The accumulation of OC in wetlands occurs when carbon fixation through net primary production exceeds decomposition through car- bon mineralization or respiration (DeBusk and Reddy, 2003), which in turn, is governed by several environmental factors, such as nutrient availability, temperature, moisture and electron acceptor availability (Reddy and D'Angelo, 1994). The decomposition of OC in wetland soils occurs at a much slower rate compared to upland ecosystems, be- cause of occasional anaerobic or sub-oxic conditions that develop as a result of flooding (Amador and Jones, 1997; DeBusk and Reddy, 2005). Furthermore, the decomposition rate of OC in wetland soils has been found to be directly influenced by the chemical and physical composition of the organic substrate with potential carbon mineraliza- tion rates decreasing with substrate age (DeBusk and Reddy, 1998). Wetlands are considered important carbon dioxide (CO 2 ) sinks and sources of atmospheric methane (CH 4 ) and although they cover only 6–8% of the earth's land and freshwater surface, they are responsible for about one-third of the global soil OC pool, con- taining about 450 × 10 15 g of OC (Mitsch and Gosselink, 2007). The amount of OC stored in wetland soils, as well as the amount of carbon emitted, is likely to change in response to climate change and anthropogenic disturbance. The Florida Everglades is the largest wetland in the United States, covering approximately 7900 km 2 from south of Lake Okeechobee to the Gulf of Mexico and Florida Bay. Surface water entering Everglades National Park (ENP), the southern-most extent of the Greater Ever- glades Ecosystem (GEE), is controlled by a series of levees and canals and comes from the Water Conservation Areas (Fig. 1), a 3400 km 2 area of shallow water reservoirs that connects ENP to the Everglades Ag- ricultural Area. In contrast to wetlands in river floodplains in tropical and sub-tropical lowlands that receive significant inputs of nutrient rich sediments and do not accumulate significant amounts of OM (Junk, 2012 and references therein) the Everglades is a naturally oligo- trophic wetland with no significant external inputs of sediments. Geoderma 241–242 (2015) 272–278 ⁎ Corresponding author at: Southeast Environmental Research Center, Florida International University, Miami, FL 33199, USA. E-mail address: scintol@fiu.edu (L.J. Scinto). http://dx.doi.org/10.1016/j.geoderma.2014.11.023 0016-7061/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma