Phosphorus loading to the northern Florida Everglades has been implicated in causing changes in vegetation, peat accretion rates, and other soil physical‐chemical properties. Our study focused on determining the influence of P loading on aerobic and anaerobic heterotrophic microbial activities (measured as CO2 and CH4 production) in detritus and soil collected from the Water Conservation Area 2a (WCA‐2a) of the Everglades. Heterotrophic microbial activities measured under both field and laboratory conditions were higher in areas impacted by P loading as compared to the unimpacted interior marsh. Microbial heterotrophic activities were higher in detritus and surface soils and decreased with depth. In field studies, CO2 production rates in anaerobic soils were approximately 64% of those observed in aerobic soils. Additions of substrates containing C, N, and P generally enhanced heterotrophic microbial activity. In laboratory studies involving addition of various inorganic electron acceptors, increased microbial activities in the order of were observed. Microbial CO2 production rates under denitrifying and sulfate reducing conditions ranged from 30–42% and 29–44%, respectively, of aerobic rates. Methane production rates were only up to 9% of aerobic CO2 production rates. Both CO2 and CH4 production rates were significantly correlated with soil P parameters and microbial biomass. Enhanced heterotrophic microbial activities resulting from P loading has the potential to increase turnover of organic matter which may lead to increased supply of bioavailable nutrients to emergent macrophytes and periphyton and higher nutrient concentrations in the water column.

The impact of P loading to the northern Florida Everglades has been implicated in changing vegetation patterns, peat accretion rates, and other soil physico‐chemical properties. This investigation focused on determining the influence of P loading on the activities of various extracellular enzymes along a P‐enrichment gradient and relating measured enzyme activities to soil physico‐chemical parameters. Alkaline phosphatase activity (APA) was the only enzyme affected by P loading and was negatively related to soil P concentrations and microbial biomass C and P. Arylsulfatase, β‐d‐glucosidase, protease, and phenol oxidase were not affected by P loading and were not related to measured soil C, N, S, and P physical and chemical parameters. All enzyme activities were highest in the surface detritus layer and decreased with soil depth. Due to significant relationships between APA and soil and microbial P parameters, APA appears to be a useful indicator for assessing impacts of P enrichment in wetland soils.

To investigate the sensitivity of labile, or active, soil organic C (SOC), such as soil microbial biomass C (SMBC), mineralizable C, particulate organic matter C (POM C), dissolved organic C (DOC), and hydrolyzable C, to changes in management, we sampled soils in a 20‐yr experiment with tillage (no‐till [NT] and conventional tillage [CT]), cropping sequence, and N fertilization treatments in south‐central Texas. Sensitivity is defined as how rapidly soil properties respond to changes in management. No‐till significantly increased the size of SOC and all labile SOC pools compared with CT, especially at 0 to 5 cm. Intensified cropping also increased SOC and these labile pools, which generally decreased with depth. Labile pools were highly correlated with each other and SOC, but their slopes were significantly different, being lowest for DOC and highest for hydrolyzable C. In our study, SMBC was 5 to 8%, mineralized C was 2%, POM C was 14 to 31%, hydrolyzable C was 53 to 71%, and DOC was 1 to 2% of SOC. Model II orthogonal regression and simple linear regression both provided similar results, indicating that both methods were appropriate for evaluation of sensitivity to changes in management; however, using our proposed equation for sensitivity to tillage, no labile SOC pool was more sensitive than SOC. Further studies are needed to examine the effectiveness of this model.

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