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Wetland Biogeochemistry Lab., Soil and Water Science Dep., 106 Newell Hall, Univ. of Florida, Gainesville, FL 32611 USA
krr{at}gnv.ifas.ufl.edu
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONStudy AreaMaterial and methodsResults and discussionSummary and conclusionsREFERENCES |
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Abbreviations: CFE, chloroform-fumigation extraction • PMN, potentially mineralizable nitrogen • SINM, substrate induced nitrogen mineralization, SFWMD, south Florida water management district • SOC, soil organic carbon • WCA-2A, Water Conservation Area-2A
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONStudy AreaMaterial and methodsResults and discussionSummary and conclusionsREFERENCES |
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Ammonification is dependent on a number of factors including the C:N ratio of the soil organic matter (SOM) and detrital tissue (Amador and Jones, 1997), temperature (Reddy, 1982; Addiscott, 1983), O2 status (Gale and Gilmour, 1988; Humphrey and Pluth, 1996), size and activity of the microbial pool (Perucci, 1990; Wardle, 1992; Amador and Jones, 1993), and limiting nutrients (Munevar and Wollum, 1977; Damman, 1988; Nair, 1996). Net N mineralization has been observed in flooded peat soils with C:N ratios of > 24:1 (Williams and Sparling, 1988), 45:1 (Humphrey and Pluth, 1996), and 80 to 100:1 (Damman, 1988). Therefore, there is little evidence that a specific C:N ratio in peat soil can be applied to predict field anaerobic organic N mineralization rates (Williams, 1984).
The microbial pool sequesters N in organic forms (proteins, amino acids) which are released upon cell death. Inorganic N, released from the organic N pool via ammonification, accumulates in wetland soils as NH+4 rather than NO-3, because of the anaerobic status of the flooded soil system (Reddy and Patrick, 1984) and diffusion limitations (Reddy et al., 1980). The high soil moisture content of peat soil restricts the supply of O2, leading to decreased organic matter decomposition rates (Humphrey and Pluth, 1996; Amador and Jones, 1997).
The availability of inorganic N in peat soils is mediated to a great extent by heterotrophic microbial activity. The soil microbial biomass has been significantly correlated with N mineralization rates in studies of wetland soils (Williams and Sparling, 1988; McLatchey and Reddy, 1998). The size and activity of the microbial pool can be regulated by the availability of nutrients. It is well established that the size of the soil microbial biomass is dependent upon the C content of soils and additions of readily hydrolyzable C sources results in increased microbial growth and activity (Anderson and Domsch, 1985; Schnurer et al., 1985). However, relationships between microbial biomass and soil organic carbon (SOC) have been shown to be strongest in soils with less than 2.5% organic C (Anderson and Domsch, 1989; Wardle, 1992) and might not be applicable to high organic matter soils (Histosols). Stimulatory responses to P additions on either microbial pool size or activity (represented by C or N mineralization rates) have been reported for a variety of ecosystems (Munevar and Wollum, 1977; Biederbeck et al, 1984; Prescott et al., 1992; Hossain et al., 1995; DeBusk and Reddy, 1998) while other studies have shown no response to P additions (Tate et al., 1991; Ross et al., 1995). Problems may exist in assessing the effect of added P on microbial properties in upland agricultural sites due to the simultaneous additions of N and P and extensive soil fertilization histories which can mask the overall effect of P addition (Wardle, 1992). All the aforementioned regulators, in concert with field scale soil heterogeneity, can make reliable bulk soil net N mineralization difficult to estimate.
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Study Area |
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TOPABSTRACTINTRODUCTIONStudy AreaMaterial and methodsResults and discussionSummary and conclusionsREFERENCES |
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1600 mg kg-1 at the surface water inflow points to background concentrations of 400 mg kg-1 in unimpacted areas, in the interior of the marsh (Koch and Reddy, 1992; Reddy et al., 1993). A gradient of N and P in surface water and periphyton tissue has also been documented along the identical transect in WCA-2A (McCormick and O'Dell, 1996). Historically, WCA-2A consisted of a P-limited sawgrass (Cladium jamaicense Crantz) marsh. The vegetation began a shift towards a dominant cattail (Typha domingensis Pers.) community proximal to all surface water inflow points (Davis, 1991; Craft and Richardson, 1997). The replacement of the natural marsh vegetative community, consisting of stands of sawgrass separated by shallow, open sloughs, by a dense cattail community could potentially affect ecosystem function.
The objectives of this study were to determine (i) the potential N mineralization rates in detritus and soil under anaerobic conditions, (ii) the relationship between soil characteristics and short-term mineralization rates under drained and flooded conditions, and (iii) the effect of added P on the size and activity of the soil microbial biomass and potential N mineralization rates in a P limited wetland soil.
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Material and methods |
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TOPABSTRACTINTRODUCTIONStudy AreaMaterial and methodsResults and discussionSummary and conclusionsREFERENCES |
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2 m along the transect length [South Florida Water Management District (SFWMD), 1996, unpublished data].
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Soil sampling was also conducted in conjunction with a mesocosm nutrient-dosing study in WCA-2A. The SFWMD established 21 circular enclosures of 1.8 m2 each, and three open control plots in an unimpacted sawgrass-periphyton-slough (McCormick and O'Dell, 1996). The mesocosm site was located approximately 11 km SW from the S-10C inflow water control structure (Fig. 1). The enclosures were installed entirely within a shallow slough that contained no stands of sawgrass within the study site proper. The soil surface was dominated by floating and benthic cyanobacterial (periphyton) mats, purple bladderwort (Utricularia purpurea Walt.), and water lily (Nymphaea odorata Ait.) (McCormick and O'Dell, 1996). At the experiment start, three replicate tanks were selected at random and spiked with various amounts of NaH2PO4 mixed with slough water to achieve loading rates of 0, 0.4, 0.8, 1.6, 3.2, 6.4, and 12.8 g P m-2 yr-1. The enclosures were perforated, which allowed exchange with the surrounding water, and equipped with sliding collars which could be moved over the holes in the side of the tanks to prevent exchange during dosing. The enclosures remained closed for 24 h after P spiking, then were subsequently opened to permit exchange with the surrounding water. These systems were dosed with P at respective levels starting in June 1995, and continued weekly for a period of 17 mo. This experiment was part of a larger ecological study conducted by McCormick and others at SFWMD (McCormick, P., 1997, personal communication).
Soil Sampling
A minimum of four soil cores were collected and composited within 5 m at each station along the transect by driving a 10-cm-diam. aluminum irrigation pipe into the soil. A probe was inserted into each core to verify that negligible (<5%) compaction had occurred during coring. Cores were sealed, removed from the ground, immediately extruded and separated into discrete soil intervals (0–10 and 10–30 cm) in the field. Each interval was well mixed to yield a representative and homogenous sample from each station. The February 1996 samples were transported to the laboratory on ice, transferred into 2-L polyethylene containers within 24 h of collection, and stored refrigerated at 4°C until analysis. Soil samples collected in August 1996 and March 1997 were immediately transported to a field "laboratory" location and incubated within 3 h of collection. Detrital material was collected during the last two sampling events for use in field incubations. Detritus consisted of recognizable, loosely packed cattail or sawgrass plant material lying on the surface of the more compact brown peat soil. The detrital layer varied in thickness from <1 cm in the sawgrass areas to >25 cm at the stations closest to the inflow. The remaining soil not utilized in field incubations was sealed in plastic bags and kept on ice until return to the laboratory where the samples were transferred into polyethylene containers and stored at 4°C until subsequent characterization.
In order to investigate spatial variability of organic N mineralization rates, three stations (2.3, 7.0, and 10.1 km from the inflow) were sampled for detritus and 0- to 10-cm soil depths along a short, east-west transect, normal to the direction of the major sampling transect, on 13 Oct. 1997. Five cores were taken at 10-m intervals, sectioned in the field, stored in plastic bags and placed on ice until return to the laboratory the following day for soil characterization and determination of the potential net N mineralization rate.
Soils were collected on 21 Nov. 1996 from the experimental mesocosms by driving a 10-cm diameter polyethylene tube into the soil. A single core was taken from each of the triplicate enclosures for all 7 P-dosing levels and three additional cores were taken from within the slough to serve as open controls (total of 24 cores). The periphyton-floc layer was poured off into separate sampling containers. The top soil interval (0–3 cm) was then extruded, stored in plastic bags and placed on ice until returning to the laboratory where samples were stored at 4°C.
Soil Characterization
Bulk density was calculated for each soil layer on a dry weight basis. Bulk density was not determined for detritus. Total C and N content of detritus and soils was determined on dried, ground samples using a Carlo-Erba NA-1500 CNS Analyzer (Haak-Buchler Instruments, Saddlebrook, NJ). Total P concentrations were determined on sub-samples by nitric-perchloric acid digestion (Kuo, 1996), followed by analysis of P by an automated ascorbic acid method (Method 365.4, USEPA, 1983).
Extractable NH4-N was determined by shaking triplicate soil samples with 25 mL of 2 M KCl at a ratio of approximately 1:40 (g dry soil:extractant) for 1 h on a longitudinal shaker. Samples were centrifuged for 10 min and vacuum-filtered through Whatman #42 filter paper. The supernatant was analyzed colorimetrically for NH4-N (Method 351.2, USEPA 1983).
Microbial biomass C was determined by the 24 h chloroform fumigation-extraction (CFE) technique after Vance et al. (1987). Triplicate, 5-g (wet weight) sub-samples were extracted with 20 mL of 0.5 M K2SO4 for 30 min on a longitudinal shaker and vacuum filtered through #42 Whatman filter paper. The supernatant was analyzed for total organic C on a Dohrman TOC analyzer (Rosemount Analytical Inc., Santa Clara, CA). Microbial biomass C was determined by subtracting the extractable total organic C (TOC) in the triplicate controls (non-fumigated) from the triplicate chloroform-treated samples. An extraction efficiency (kEC) factor of 0.37 was applied, utilizing a previously determined calibration for organic soils by Sparling et al. (1990). The values of TOC for the non-fumigated (control) samples were defined as extractable or labile C.
Microbial biomass N was determined by the CFE technique after Brookes et al. (1985). Ten milliters of extract from the microbial carbon procedure were subjected to Kjeldahl-N digestion using the salicylic acid modification of Bremner and Mulvaney (1982). Extracts were analyzed for NH4-N colorometrically (Method 351.2, USEPA, 1983). Microbial biomass N was determined by subtracting the extractable NH4-N concentrations of the triplicate non-fumigated samples from triplicate fumigated samples. A combined extraction efficiency value (kEN) of 0.54 was applied (Brookes et al., 1985).
Potentially Mineralizable Nitrogen (PMN) Rate
We define the potentially mineralizable N (PMN) rate as an anaerobic, waterlogged incubation at 40°C (Keeney, 1982). The PMN rates of soils and detritus were determined for samples collected from along the transect (February 1996; August 1996; March 1997), the spatial study samples (October 1997), and from the mesocosm field trial (November, 1996). Glass serum bottles were prepared by adding 10 g of moist soil and 5 mL of distilled, de-ionized water. Bottles were capped with butyl rubber stoppers and sealed with aluminum crimps. The headspace was evacuated and replaced with 99.99% O2-free N2 gas. Triplicate serum bottles were incubated in the dark at 40°C for 10 d. Selected serum bottles were monitored over the course of the incubation to insure continuous anaerobic conditions by gas chromatography. At the terminus of the incubation, samples were extracted with 30 mL of 2 M KCl. Bottles were shaken for 1 h on a longitudinal shaker and centrifuged for 10 min at 4000 g. The supernatent was filtered through Whatman #42 filter paper and refrigerated at 4°C for subsequent automated, colorimetric analysis (Method 351.2, USEPA 1983).
Substrate Induced N Mineralization (SINM)—Field Study
Differences in net N mineralization can be investigated over short time periods (h) with simple substrates (amino acids) because the rate limiting steps of soil organic matter decomposition have been removed by providing a readily hydrolyzable substrate. Soil and detritus were collected for a field study at eight stations along the study transect in August 1996 and March 1997. After thorough mixing, large (100 g) subsamples were taken and split into two groups; one set for incubation under drained conditions and the other for flooded conditions. Moisture was removed from the drained samples by spreading thin layers of soil and detritus on dry sponges covered by sheets of glass fiber filter paper for 20 to 30 min. Soils utilized in the anaerobic incubations remained in field saturated condition (flooded).
The following procedure was used at each station. Approximately 10 g of drained soil per station and depth increment were added to 250-mL Nalgene (Nalge Nunc International, Rochester, NY) polyethylene bottles for aerobic incubations and 10 g of field moist soil were added to 250-mL air-tight centrifuge tubes for anaerobic incubation. To triplicate samples of drained and flooded samples, 1.0 mL of solution containing 400 mg L-alanine (C3H7NO2)-N L-1 was added by mechanical pipette. Samples were well mixed to distribute the spike solution and soil aggregates were broken up with a glass rod to maximize the soil volume in contact with air (drained samples). Drained sample bottles were capped, incubated in the dark, and submerged in site water for 4 h at ambient temperature (28–31°C). Flooded sample bottles were capped, purged with O2-free (99.99% pure) N2 gas for 5 min, incubated in the dark, and submerged in site water for 4 h at ambient temperature. Triplicate controls (no substrate added) were included for the drained and flooded treatments. All samples were extracted at the terminus of the incubation with 50 mL of 2 M KCl. Bottles were agitated on a longitudinal shaker for 1 h and vacuum filtered through #42 Whatman filter paper. The supernatant was collected and kept on ice until returning to the laboratory, then stored at 4°C until subsequent automated colorimetric analysis for NH4-N (Method 351.2, USEPA 1983).
Phosphorus Addition—Laboratory Study
Surface soil (0- to 10-cm interval) from station 10 (10.1 km from the inflow) was collected to determine the effect of added inorganic P on net N mineralization rates in unimpacted soil. The soil was homogenized by mechanical mixing after removing live roots. Samples were pre-incubated for 20 d by placing approximately 50 g of field moist soil in 120 mL media. To each bottle, 40 mL of distilled deionized water was added and mixed well with the soil. The following treatments were evaluated: (i) control-no addition and (ii) NaH2PO4 added (0.1, 1.0, 5.0, 10 mg P L-1 final concentration in the porewater). Each treatment was performed in triplicate. Bottles were capped and purged with O2-free N2 gas to create anaerobic conditions. Samples were incubated in the dark at 30°C for 20 d and were shaken by hand for 30 s each day. Triplicate soil controls were spiked with distilled de-ionized water. The 20-d, pre-incubation period allowed the microbial community time to react to added P. At the terminus of the 20-d incubation, 20 mL of soil-water slurry was collected from each bottle by pipette, and extracted with 20 mL of 2 M KCl to determine the extractable NH+4 (Method 351.2, USEPA 1983). An additional 10 mL were placed in air-tight serum bottles under a O2-free N2 headspace for incubation at 40°C for 10 d to determine the effect of differential P additions on PMN rates.
Data Analysis
Soil characteristics and parameters were statistically related by Pearson's product-moment correlation and regression analysis. Data were fitted to an ANOVA model to investigate significant differences (P < 0.05) in soil characteristics and potential N mineralization rates among soil intervals (depth), distance from inflow, and P addition rates (laboratory and field). Soil characterization data from three separate samplings along the transect were utilized to calculate mean and standard deviation for bulk density, total C, N, and P. Fisher's Least Significant Difference (LSD) test was utilized to determine significant difference between treatments for the nutrient addition study using the StatGraphics software program (Manugistics, Inc., Rockville, MD).
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Results and discussion |
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TOPABSTRACTINTRODUCTIONStudy AreaMaterial and methodsResults and discussionSummary and conclusionsREFERENCES |
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for all samplings of detritus and soil along the transect. The mean C:N ratio was 16:6 and failed to demonstrate a significant correlation with distance from the inflow.
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with distance from the inflow for all samples combined. Regression analysis of the total P data with distance yielded model R2 values of 0.88, 0.91, and 0.80, for detritus, 0 to 10, and 10 to 30 cm, respectively. Total P was also correlated (P < 0.01) with depth
, with significantly higher (P < 0.05) total P concentrations in both detritus and 0- to 10-cm soil depths than in the underlying 10- to 30-cm soil depth. There was no significant difference between total P content of detritus and the 0- to 10-cm soil layer. The N:P ratio of soil and detritus increased with distance from inflow for detritus and soil (P < 0.01).
Extractable NH+4 was negatively correlated (P < 0.01) with depth averaging 377 ± 193, 122 ± 56, and 55 ± 24 mg N kg-1 for the detrital, 0- to 10-cm and 10- to 30-cm soil depths combining all the data from the three samplings from the eight stations. Decreasing concentrations of extractable NH+4 in soils with increasing depth have been noted by others (Humphrey and Pluth, 1996). There was a significant correlation with extractable NH+4 with total P
suggesting a possible relationship between inorganic N availability and total P along the transect.
In the experimental mesocosms, soil bulk density did not vary significantly among treatments (P > 0.9) and averaged 0.093 ± 0.012 g cm3 for the 0- to 3-cm soil depth (Table 2)
. Total C and N values did not vary significantly among treatments and were significantly correlated with each other
. The mean C:N ratio was 13.1 ± 0.54 for the 0- to 3-cm surface soil. Total P of soil was significantly correlated
to the experimental P loading rate indicating that P was not completely scavenged by the benthic periphyton–floc layer (Table 2). A significant decrease in the N:P ratio of the 0- to 3-cm soil was observed with increased P loading, ranging from a mean 75:1 in the no dose treatment to 40:1 in the highest P dose treatment. Extractable NH+4 was significantly correlated
to soil total P in the mesocosm field study further suggesting a possible relationship between N and P.
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and N
in the detritus were each negatively correlated (P < 0.01) with distance from the inflow point along the transect. A significant correlation was observed for microbial biomass C and N vs total P
for the detrital layer, suggesting that P-loading at the inflow point, might have some relationship to the increased size of the microbial biomass.
Microbial biomass C and N both decreased with depth along the transect
pooling data for all stations with respect to depth. Microbial biomass C averaged 13.3, 4.8 and 1.6 g kg-1 and microbial biomass N averaged 1090, 347, and 109 mg kg-1 for detritus, 0 to 10 cm and 10 to 30 cm, respectively (Fig. 2)
. DeBusk (1996) found that the lignin:cellulose increased with depth in these soils which suggests the decrease in microbial biomass C and N with depth is likely due to the lower availability of C to support microbial populations in the subsurface and is similar to results found by others (Williams and Sparling, 1988; Franzluebbers et al., 1995; DeBusk and Reddy 1998).
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, and
and microbial biomass N averaged
, and
as a percentage of total N for detritus, 0- to 10-cm, and 10- to 30-cm depths, respectively. These results suggest that detritus is the most microbiologically active portion of the wetland soil profile and is likely to be responsible for the greatest amount of nutrient turnover–release.
A significant correlation was observed between microbial biomass C and N from the transect study
with the C:N ratio averaging 12.3, 13.9 and 14.7 for detritus, 0- to 10-cm, and 10- to 30-cm soil depths, respectively. A regression of microbial C vs N yielded an average C:N ratio of 11.4 for the microbial pool
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The mean microbial biomass C of the 0- to 3-cm depth soil from the P-dosing study was 7.1 g kg-1 while microbial biomass N averaged 519 mg N kg-1. A strong correlation between microbial biomass C and N was observed
and the slope of the regression returned an average C:N ratio of 9.9 for the microbial pool. The similarity in average C:N ratio of microbial pools from the transect and mesocosm studies does not address the differences in the relative, functional, microbial pool composition along the transect (Drake et al., 1996). Mean microbial biomass C as a percentage of total C and microbial biomass N as a percentage of total N in the P-dosing study were
and
, respectively. These values were higher than the values for the 0- to 10-cm depth but lower than from the detrital layer along the transect.
Microbial biomass N was significantly correlated with P-loading rate
for the 0- to 3-cm soil depth. Both microbial biomasss C and N were positively, significantly correlated with soil total P
providing evidence that P was likely the limiting nutrient to the microbial biomass in natural Everglades peat soils.
Potentially Mineralizable Nitrogen Rate
Potentially mineralizable nitrogen rates from along the transect were highest in the detrital layer, decreasing with depth averaging 126, 35.8, and 18.2 mg N kg-1 d-1 for detritus, 0- to 10- and 10- to 30-cm soil depth, respectively (Fig. 3)
. A similar pattern of decreasing N mineralization with depth has been observed by others in aerobic soils (Franzluebbers et al., 1996; Hossain et al, 1995). There existed a significant negative correlation of PMN rate with distance from inflow for all sample intervals combined
, as well as for each depth interval taken separately, with the most significant effect seen in detritus samples
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Overall, PMN rates were significantly correlated with several soil properties including microbial biomass
and extractable NH+4
with significant negative correlations with total N
. These relationships might be useful in assisting in the development of diagnostic biogeochemical indicators, however care should be taken to examine each relationship before proceeding from correlation to causation (regression). The organic rich Everglades soils have a low redox potential and contain a thin (2–4 mm) oxidized layer due to high available C coupled with high microbial activity (DeBusk, 1996). The low O2 status of the soil can result in the near complete inhibition of the autolithotrophic conversion of NH+4 to NO-3. Therefore, the concentration of extractable NH+4 might provide a good indication of in situ N mineralization rates in flooded soils (Ross et al., 1995; Williams and Sparling, 1988).
The strong relationship of PMN rate with the size of the microbial pool is likely one of causation. Mineralization is a microbial-mediated process and given a substrate (SOM) with a similar C:N ratio, one could expect differences in total active microbial biomass to influence the rate at which inorganic N is liberated from the organic fraction.
The mesocosm experiment provided an excellent opportunity for a separation of effects in the field, as P was loaded at several rates to soil at the same station containing similar vegetative characteristic and presumably, similar microbial populations. Unlike the transect study, where vegetation type and density as well as functional microbial communities varied (Drake et al., 1996), any differences in soil characteristic or microbial processes should be directly attributed to P enrichment.
Total P was significantly, positively correlated with both microbial biomass C and N in the P-dosing study, suggesting a P limitation to the microbial pool. In addition, total P was significantly (P < 0.01) correlated with PMN rate indicating an increase in inorganic N release from soil with increasing total P. These results suggests that total P was a reliable indicator of microbial activity. A similar P limitation to organic N mineralization was found for a volcanic ash (Inceptisol) soil (Munevar and Wollum, 1977) and a peat soil (Histosol) from the Everglades National Park (Nair, 1996).
Combining all the data from the transect and mesocosm studies, the best fit regression model of PMN vs total P was significant at P < 0.01 (Fig. 4) . These results suggest that organic N mineralization rates in WCA-2A were likely controlled by availability of P to the microbial pool.
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times greater than SINM rates under flooded conditions. The best-fit linear regression between drained and flooded SINM rates yielded a slope of 2.14 (Fig. 7)
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There was found a significant (P < 0.05) weak correlation between SINM and distance from inflow for both drained and flooded samples
. A highly significant (P < 0.001) seasonal effect was found with higher ammonification rates in the summer (August 1996) when compared with the winter (March, 1997). A portion of the difference in rates can be attributed to differences of in situ field incubation temperatures (6°C) between sampling dates. Total P was not significantly correlated with either drained or flooded SINM.
Extractable NH+4 exhibited a significant weak correlation to SINM
for both drained and flooded samples. This result is expected, as extractable NH+4 concentrations in the soil are a direct result of net N mineralization processes. The microbial biomass C and N pools were significantly correlated to SINM for the flooded samples. The size of the microbial pool, represented by MBN for the drained samples, was also significantly correlated with SINM. The release or de-amination of NH+4 from amino acids has been seen by others in lake systems where N was not limiting (Gardner et al., 1987; Hollibaugh, 1978). The SINM rates were not strongly correlated with measured soil properties and therefore, does not appear to be a useful assay for determining relative rates of potential organic N mineralization in these soils.
There was a significant difference (P < 0.001) in N mineralization rates of native organic matter and L-alanine, with the average PMN rate 23 times slower than the SINM rates, after a temperature correction for potential N mineralization rates (Q10 of 2). Similar results have been observed for amino acid utilization in lake water (Gardner et al., 1986, 1989) and in soil samples (Alef and Kleiner, 1986). The large difference in ammonification rates between the two parameters (PMN and SINM), lends additional support to the theory that organic N mineralization is limited by the breakdown of larger, more complex compounds while simple amino acids compounds are quickly attacked and utilized by the microbial populations.
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Summary and conclusions |
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TOPABSTRACTINTRODUCTIONStudy AreaMaterial and methodsResults and discussionSummary and conclusionsREFERENCES |
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In summary, eutrophication due to P-loading has appeared to increase the turnover rates of inorganic N from soil and detritus, linked to an increased activity and size of the microbial pool. The microbially mediated mobilization of nutrients, through increased decomposition, has led to an increased availability of inorganic N in the soil. The increased availability of inorganic N could potentially stimulate plant growth. The significant relationship of microbial biomass components to heterotrophic microbial activity (N mineralization) has demonstrated the influence the microbial biomass can exert on concentrations of extractable NH+4 in detritus and soil. This result may possibly affect the overall wetland water quality and species composition of the northern Everglades system.
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ACKNOWLEDGMENTS |
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REFERENCES |
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TOPABSTRACTINTRODUCTIONStudy AreaMaterial and methodsResults and discussionSummary and conclusionsREFERENCES |
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and one standard error for February 1996, August 1996, and March 1997 sampling dates
