Cladium Jamaicense Research Articles

Nutrient and Hydrology Effects on Soil Respiration in a Northern Everglades Marsh

Microbial respiration in peat and overlying plant litter, as influenced by water level and phosphorus enrichment, was evaluated for an Everglades (Florida, USA) marsh ecosystem by measuring CO2 and CH4 release from soil–water microcosms. Intact cores of peat, overlying plant litter, and surface water were collected at seven locations in cattail (Typha domingensis Pers.) and sawgrass (Cladium jamaicense Crantz) stands along a phosphorus (P) enrichment gradient in Water Conservation Area 2A (WCA-2A). Each soil–water microcosm was outfitted with a controlled air circulation system whereby outflow gas from the headspace could be analyzed for CO2 and CH4 to determine flux of C from the soil–water column to the atmosphere. Gaseous C flux was determined for flooded conditions (10-cm water depth) and for water levels of 0, 5, 10, and 15 cm below the peat surface. Overall, decreasing water level resulted in significantly increased C flux, although rates were significantly higher under flooded conditions than under nonflooded, saturated-soil conditions, presumably due to O2 availability associated with algal photosynthesis within the litter layer in the water column. Carbon flux decreased significantly for sites increasingly distant from the primary hydrologic and nutrient inflows to WCA-2A. The microcosm study demonstrated that the C turnover rate was significantly increased by accelerated nutrient loading to the marsh, and was further enhanced by decreasing water level under drained conditions. Our results also demonstrated that photosynthesis within the water column is a potentially important regulator of C mineralization rate in the litter layer of the marsh system.

Phosphatase activity as an early warning indicator of wetland eutrophication: problems and prospects

A phosphorus (P) loading experiment conducted in the oligotrophic P-limited Everglades was used to assess the utility of phosphatase activity (PA) of periphyton as an early warning (EW) indicator of wetland eutrophication. Phosphorus loads of 0, 0.4, 0.8, 1.6, 3.2, 6.4 and 12.8 g P m−2 yr−1 were applied to mesocosms placed in a slough community consisting of Cladium jamaicense Crantz, Eleocharis spp. and calcareous periphyton mats. Phosphatase activity, expressed on a biomass-specific basis, was not a sensitive indicator of P enrichment for epiphytic periphyton growing on acrylic dowels or floating mat periphyton. However, surface-area-specific PA was a sensitive indicator of P enrichment, responding within 2–3 weeks of the initiation of dosing. Surface-area-specific PA of unenriched periphyton ranged from 0.42 to 0.7 nmol cm−2 min−1, while PA of periphyton growing in the highest load (12.8 g P m−2 yr−1), ranged from 0.11 to 0.29 nmol cm−2 min−1. Conclusions drawn from PA analyses were consistent with those obtained from periphyton primary productivity and P content. Phosphatase activity is a potentially valuable EW indicator when used in conjunction with other complementary indicators.

Root phosphatase activity in Cladium jamaicense and Typha domingensis grown in Everglades soil at ambient and elevated phosphorus levels

Activity of root phosphatase was examined in Cladium jamaicense (sawgrass) and Typha domingensis (cattail) grown under controlled conditions in Everglades peat with different inorganic P availabilities and flooding regimes. Cladium root phosphatase activity was significantly greater than for Typha when both were subjected to relatively low inorganic phosphorus concentrations (10 to 80 μg l−1) in the interstitial water, indicating a greater potential for Cladium to use organic phosphorus compounds as a phosphate source. When inorganic phosphorus concentration was elevated (500 μg l−1), internal root phosphate concentrations increased and root phosphatase activities decreased in both species to similar levels. Thus, root phosphatase activity in these species is induced by low ambient inorganic phosphate concentrations. The relatively greater ability of Cladium to hydrolyze organic phosphorus compounds indicates that it is physiologically better adapted to peat-based, low inorganic phosphorus conditions and helps explain this species’ historic dominance in peat-based Everglades soils.

EVAPOTRANSPIRATION MEASUREMENT AND ESTIMATION OF THREE WETLAND ENVIRONMENTS IN THE UPPER ST. JOHNS RIVER BASIN, FLORIDA1

ABSTRACT: Accurate estimates of evapotranspiration from areas dominated by wetland vegetation are needed in the water budget of the Upper St. Johns River Basin. However, local data on evapotranspiration rates, especially in wetland environments, were lacking in the project area. In response to this need, the St. Johns River Water Management District collected evapotranspiration field data in Fort Drum Marsh Conservation Area over the period 1996 through 1999. Three large lysimeters were installed to measure the evapotranspiration from different wetland environments: sawgrass (Cladium jamaicense), cattail (Typha domingensis), and open water. In addition, pan evaporation was measured with a standard class “A” pan. Concurrently, meteorological data including rainfall, solar radiation, wind speed, relative humidity, air temperature, and atmospheric pressure were collected. By comparing computed evapotranspiration rates with those measured in the lysimeters, parameters in the Penman‐Monteith, the Priestley‐Taylor, and Reference‐ET methods, and evaporation pan coefficients were estimated for monthly and seasonal cycles. The results from the data collected in this study show that mean monthly evapotranspiration rates, computed by the different methods, are relatively close. From a practical point of view, results indicate that the evaporation pan can be used equally well as the more complex and data‐intensive methods. This paper presents the measured evapotranspiration rates, evaporation pan coefficients, and the estimated parameter values for three different methods to compute evapotranspiration in the project area. Since local data on evaporation are often scarce or lacking, this information may be useful to watershed hydrologists for practical application in other project regions.

Flower and spikelet morphology in sawgrass, Cladium jamaicense Crantz (Cyperaceae).

In recent systematic treatments of the Cyperaceae, spikelets of all but the most primitive tribes have been considered to be indeterminate, whereas historically the number of flowers, floral sex and distribution of sexes in spikelets have been important characters in suprageneric classifications. However, descriptions of these spikelet characteristics for sawgrass, Cladium jamaicense Crantz, vary among authors. Spikelet morphology was analysed using developmental and phenological studies of sawgrass populations in south Florida, USA. Sawgrass spikelets have two flowers that expand successively. Flowers are fundamentally hermaphroditic and protogynous. The first flower to expand (F1) terminates the spikelet axis, whereas the second flower (F2), ensheathed by an addorsed prophyll, develops in the axil of the last bract produced on the axis. In 86% of the spikelets examined from ramets of three populations, the gynoecium of the F1 flower aborted, so this flower was functionally male and the spikelet was protandrous. However, in 14% of spikelets from these individuals, the F1 flower was hermaphroditic and could set seed. The F2 flower was typically hermaphroditic and matured stigmas, then anthers. Thus, spikelets in C. jamaicense are determinate and have two flowers that are dichogamous both within flowers and between flowers in a spikelet; spikelet sex expression can vary among plants and populations, especially in the first flower. These data for sawgrass suggest that a re-examination of spikelet development and phenology in other genera is needed to clarify the expression of these characters in the family.

EFFECTS OF FIRES ON FORAGING AND BREEDING WADING BIRDS IN THE EVERGLADES

Nests, eggs, and chicks of nesting wading birds were unharmed by two fires in the Everglades. However, at least 50 adult White Ibises (Eudocimus albus) foraging away from the breeding colonies were killed during one fire. These results are counter-intuitive given that well-flighted adult birds seem more capable of escaping a fire than immobile nests or eggs. Nests probably were unharmed because of their location in wet willow (Salix carolina) and buttonbush (Cephalanthus occidentalis) islands. The adult birds foraging in a small cattail (Typha angustifolia) stand may have been trapped by flames in surrounding tall sawgrass (Cladium jamaicense) or debilitated by smoke inhalation. These observations provide insight into the direct effects of fire on wading bird breeding colonies and individual survival.

Genotypic Diversity and Clonal Structure of Everglades Sawgrass,Cladium jamaicense(Cyperaceae)

The extent of asexual reproduction and the spatial distribution of clones can influence ecological and evolutionary processes in populations. Sawgrass, Cladium jamaicense, which is the dominant ecosystem component in the Florida Everglades, can reproduce sexually and asexually. We examined patterns of genotypic diversity and evaluated the importance of clonal reproduction in Everglades populations of C. jamaicense, using allozymes as genetic markers. We sampled plants in a replicated grid along 11‐m transects in 18 populations of sawgrass distributed throughout the Everglades. Genotypic diversity was low in Everglades sawgrass populations, compared with other plants (mean [SE] number of multilocus genotypes per populatio \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\c...

Genetic Diversity of Everglades Sawgrass,Cladium jamaicense(Cyperaceae)

Genetic diversity studies of wetland plants are scarce, but estimates of genetic diversity are useful for learning about plant biology or developing appropriate management strategies. We used allozymes to examine patterns of genetic diversity in Cladium jamaicense, the dominant plant species of the Florida Everglades. We sampled 18 populations (a total of 818 plants) in a replicated grid pattern. Because C. jamaicense can reproduce asexually, we compared estimates of genetic diversity calculated using all sampled ramets to those using only genets within populations. Fewer than half of the 13 loci studied were polymorphic ($$P_{\mathrm{s}\,}=46.2\% $$), with just under two alleles per locus on average ($$A_{\mathrm{s}\,}=1.9$$). Heterozygosity was also low and was lower for ramet‐level estimates (ramets: $$H_{\mathrm{es}\,}=0.069$$, $$H_{\mathrm{ep}\,}=0.051$$; genets: $$H_{\mathrm{es}\,}=0.094$$, $$H_{\mathrm{ep}\,}=0.067$$). Ramet‐level estimates indicated heterozygote excess in eight populations and heterozygote deficiencies in four populations, but genet‐level estimates indicated inbreeding in only one population. Ramet‐level estimates indicated significant population differentiation ($$F_{\mathrm{ST}\,}=0.268$$), but genet‐level estimates did not ($$F_{\mathrm{ST}\,}=0.035$$). Similarly, mean genetic distance between populations was higher based on ramet‐level estimates ($$\overline{D}=0.024$$) than genet‐level estimates ($$\overline{D}=0.016$$), and we found a weak correlation between genetic and geographic distance based on ramet‐level estimates ($$r=0.15$$, $$P=0.02$$) but not genet‐level estimates ($$r=0.04$$, $$P=0.2$$). Thus, clonal reproduction resulted in effective genetic differentiation among populations. Observed patterns of population differentiation may reflect high levels of gene flow among populations or patterns established during colonization that persist through long‐lived clones. Genetic diversity of Everglades C. jamaicense was low compared to other sedges or other species with similar life histories (ramets: $$H_{\mathrm{T}\,}=0.150$$; genets: $$H_{\mathrm{T}\,}=0.203$$). This low genetic diversity may reflect a relatively recent origin of C. jamaicense populations in south Florida.

THE ROLE OF SOIL FERTILITY IN INVASION OF BRAZILIAN PEPPER (SCHINUS TEREBINTHIFOLIUS) IN EVERGLADES NATIONAL PARK, FLORIDA1

Brazilian pepper (Schinus terebinthifolius Raddi), an exotic invasive plant, is native to South America. In south Florida, this plant has invaded abandoned agricultural lands, poorly managed pastures, roadsides, and canal banks extensively. The Hole-in-the Donut (HID), approximately 4000 ha within the Everglades National Park, is a major site of invasion of this exotic plant. This area was previously short hydroperiod prairie and pineland, but it is now a monospecific stand of Brazilian pepper. It has been hypothesized that this transformation is related to rock-plowing soil (crushing the limestone bedrock to increase soil depth) and to intensive vegetable production 25 to 70 years ago. The objectives of this study were to compare the chemical and physical differences of soils from four land uses (undisturbed land, rock-plowed farm land, non-rock-plowed farm land, and restored land) and the mineral nutrient contents of Brazilian pepper and sawgrass (Cladium jamaicense Crantz). Farming in the HID area changed the soil chemical properties significantly through rock-plowing and the application of agrichemicals necessary for commercial vegetable production. Rock-plowing increased the percenage of rock fragments and the soil pH. Total concentrations of nutrients (N, P, Zn, and Cu) in soils were elevated in both rock-plowed and non-rock-plowed farm lands. Plant-available nutrients in soil of rock-plowed farm land increased about 3 times for P, 6 times for Zn, and 10 times for Cu. As a result of the increased soil fertility, concentrations of P and Zn in Brazilian pepper leaves were 5 and 3 times higher, respectively, than those in sawgrass. High correlation coefficients between leaf P and total and plant-available P in soils indicate that P enrichment in farmed soils facilitated the invasion of Brazilian pepper in this area.

Growth, biomass allocation and nutrient use efficiency in Cladium jamaicense and Typha domingensis as affected by phosphorus and oxygen availability

The effects of phosphorus (P) and oxygen availability on growth, biomass allocation and nutrient use efficiency in Cladium jamaicense Crantz and Typha domingensis Pers. were studied in a growth facility equipped with steady-state hydroponic rhizotrons. The treatments included four P concentrations (10, 40, 80 and 500 μg l −1) and two oxygen concentration (8.0 and <0.5 mg O 2 l −1) in the culture solutions. In Cladium, no clear relationship was found between P availability and growth rate (19–37 mg g −1 d −1), the above to below ground biomass ratio ( A/ B) (mean=4.6), or nitrogen use efficiency (NUE) (mean=72 g dry weight g −1 N). However, the ratio between root supported tissue (leaves, rhizomes and ramets) and root biomass ( S/ R) (5.6–8) increased with P availability. In contrast, the growth rate (48–89 mg g −1 d −1) and the biomass ratios A/ B (2.4–6.1) and S/ R (5.4–10.3) of Typha increased with P availability, while NUE (71–30 g dry weight g −1 N) decreased. The proportion of root laterals was similar in the two species, but Typha had thinner root laterals (diameter=186 μm) than Cladium (diameter=438 μm) indicating a larger root surface area in Typha. The two species had a similar P use efficiency (PUE) at 10 μg P l −1 (mean=1134 g dry weight g −1 P) and at 40 and 80 μg P l −1 (mean=482 dry weight g −1 P) but the N/P ratio indicated imbalances in nutrient uptake at a higher P concentration (40 μg P l −1) in Typha than in Cladium (10 μg P l −1). The two species had similar root specific P accumulation rate at the two lowest P levels, whereas Typha had 3–13-fold higher P uptake rates at the two highest P levels, indicating a higher nutrient uptake capacity in Typha. The experimental oxygen concentration in the rhizosphere had only limited effect on the growth of the two species and had little effect on biomass partitioning and nutrient use efficiency. The aerenchyma in these species was probably sufficient to maintain adequate root oxygenation under partially oxygen depleted conditions. Cladium had characteristics typical for plants from nutrient poor habitats, which included slow growth rate, low capacity for P uptake and relatively inflexible biomass partitioning in response to increased P availability. In contrast, Typha demonstrated a high degree of flexibility in growth, biomass partitioning, and nutrient accumulation to P availability, similar to species from nutrient rich habitats. Although the N/P ratio indicated that Typha was more nutrient stressed at the low P levels, Typha had a higher capacity for P uptake and was more competitive than Cladium at the applied P concentrations.

Fate of oxygen losses from Typha domingensis (Typhaceae) and Cladium jamaicense (Cyperaceae) and consequences for root metabolism

The objective of this work was to determine whether radial oxygen loss (ROL) from roots of Typha domingensis and Cladium jamaicense creates an internal oxygen deficiency or, conversely, indicates adequate internal aeration and leakage of excess oxygen to the rhizosphere. Methylene blue in agar was used to visualize the pattern of ROL from roots, and oxidation of a titanium-citrate solution was used to quantify rates of oxygen leakage. Typha's roots had a higher porosity than Cladium's and responded to flooding treatment by increasing cortical air space, particularly near the root tips. A greater oxygen release, which occurred along the subapical root axis, and an increase in rhizosphere redox potential (E(h)) over time were associated with the well-developed aerenchyma system in Typha. Typha roots, regardless of oxygen release pattern, showed low or undetectable alcohol dehydrogenase (ADH) activity or ethanol concentrations, indicating that ROL did not cause internal deficiencies. Cladium roots also released oxygen, but this loss primarily occurred at the root tips and was accompanied by increased root ADH activity and ethanol concentrations. These results support the hypothesis that oxygen release by Cladium is accompanied by internal deficiencies of oxygen sufficient to stimulate alcoholic fermentation and helps explain Cladium's lesser flood tolerance in comparison with Typha.

Fungal and bacterial contributions to the decomposition of Cladium and Typha leaves in nutrient enriched and nutrient poor areas of the Everglades, with a note on ergosterol concentrations in Everglades soils

Fungal biomass was detected in peat soils from throughout the Everglades based on the presence of ergosterol. Ergosterol concentrations in soils were not detectably affected by the dominant plant, Cladium jamaicense or Typha domingensis , or phosphorus content of soils. In situ decomposition of decaying leaves, measured by respiration, was high (maximum 484 ul O 2 h −1 g −1 dry biomass). Approximately 30% of respiration was by bacteria, and the rest was by fungi and other eukaryotes. Respiration rates were essentially the same for decomposing leaves of both plant species, with higher rates early in the decomposition process. Respiration rates were relatively unaffected by the nutrient status of the site, except for eukaryotic respiration on Cladium , which was usually higher at a high nutrient site. Ergosterol concentration increased in decaying leaves through time and was unrelated to the nutrient level except for Cladium , where it was higher at the high nutrient site. Eukaryotic respiration was not correlated with ergosterol concentration in decomposing leaves of Typha , but was positively correlated with ergosterol for Cladium.

Seed germination of two Everglades species, Cladium jamaicense and Typha domingensis

The germination requirements of Cladium jamaicense Crantz and Typha domingensis Pers. were studied under controlled conditions in the laboratory. Treatments included six temperature regimes, (constant temperatures of 15 20, 25, 30°C, and two fluctuating day : night temperature regimes of 25 : 10°C and 30 : 20°C), two light levels (14 : 10 h light : dark photoperiod and 24 h dark environment), two substrates (peat and water) and two O 2 levels (atmospheric and low (4.34%) O 2 concentration) using a complete randomized block design. The average incubation period needed for seeds to germinate was shorter for T. domingensis (1.1–19.5 days) than for C. jamaicense (26–46 days) and the final germination percentage was higher for T. domingensis than for C. jamaicense (85 vs. 42 %). Cladium jamaicense only germinated with fluctuating temperatures whereas T. domingensis germinated at all temperature regimes. Light was required for T. domingensis seeds to germinate, whereas C. jamaicense could germinate at a reduced rate in the dark. Peat substrate had a positive effect on germination in both species. Peat substrate shortened the incubation period for seeds of both species, enhanced germination of T. domingensis, especially at low temperatures, and enhanced germination of C. jamaicense in the dark. Low oxygen availability did not influence the germination of C. jamaicense but enhanced germination of T. domingensis at low temperatures. Although the two species differ significantly in their germination requirements and responses to specific environmental conditions, germination of both these species was enhanced by environmental conditions typical of exposed water saturated mudflats or sediment surfaces. Typha domingensis produces a large number of small seeds, which do not germinate when covered by sediment. In contrast, C. jamaicense produces fewer and larger seeds, with resources able to support growth through a thin layer of sediment or detritus.

Phosphorus Enrichment Affects Litter Decomposition, Immobilization, and Soil Microbial Phosphorus in Wetland Mesocosms

Like many wetland ecosystems, areas of the northern Everglades of Florida, USA, have been influenced by P eutrophication. Our objective was to determine if P enrichment of water influences the litter decomposition rate and nutrient immobilization by litter and, further, to determine the quantitative relationship of these responses across a range of P concentrations in surface water. In addition, we determined whether P additions rapidly elevated microbial biomass P in the soil. In order to isolate the effects of P enrichment, we placed bags containing cattail (Typha domengensis Crantz) and sawgrass (Cladium jamaicense Pers.) litter into two sets of experimental channels into which controlled inputs of five different phosphate concentrations were added continuously. After 1 yr of incubation, litter was analyzed for C, P, N, Cu, Ca, and K content. Loss of C at the end of 1 yr increased linearly with increasing average PO4 content in the channels with a similar slope for both species of litter. Immobilization caused an absolute increase in P content of the litter up to approximately ninefold across the range of water P concentrations, while immobilization of N, Ca, and K did not vary with water P concentrations. During decomposition, litter exhibited a net uptake of Cu (a nutrient potentially limiting plant growth on peat soils). The microbial biomass P was up to nine times higher in the surface soil of the most enriched channel compared with the control, but this elevation in concentration was restricted to the upper 12 cm of soil.

NUTRIENT EFFECTS ON STAND STRUCTURE, RESORPTION EFFICIENCY, AND SECONDARY COMPOUNDS IN EVERGLADES SAWGRASS

Long-term studies along a 30-yr nutrient-enrichment gradient in the northern part of the subtropical Everglades fen allowed us to assess the effects of nitrogen (N) and phosphorus (P) additions on plant community structure and chemical qualities of wetland plants. Areas in the highest P-enriched zones (>1000 mgP/kg), once dominated by open-water sloughs and surrounding monocultures of sawgrass (Cladium jamaicense, a stress-tolerant low-nutrient-status species), are now dominated by cattail (Typha domingensis, a competitive, high-nutrient-status species). Areas of moderate (750–500 mg/kg) and low (<500 mg/kg) P soil concentrations have maintained their original plant composition. Analysis of nutrient-use efficiency indicates that sawgrass is highly efficient in nutrient resorption and nutrient proficiency, but this efficiency decreases at high soil P concentrations. Both indices indicate that suboptimal concentrations of P, which limit growth and optimize retention of P within the plant, exist in the Everglades. This information, when coupled with the low levels of P found in the plants, soil, and pore water of the unenriched portions of the Everglades, indicates that this ecosystem is extremely P limited. High molar N:P leaf ratios suggested P limitations for sawgrass at unenriched sites, but not in highly enriched areas. Intermediate P loadings resulted in either N or P limitations. Increased leaf P concentrations correspond to decreased phenolic content of sawgrass leaves, suggesting that this species’ metabolic growth response follows the carbon–nutrient balance hypothesis of decreased production of phenolics with increased nutrient supply. Concomitant with decreased foliar phenolic content at high P enrichment was an increase in herbivory and fungal infections.

Macrophyte Species Changes in the Everglades: Examination along a Eutrophication Gradient

AbstractMacrophyte species distribution in the marsh and slough areas of the northern Everglades were examined along a surface water and soil P gradient to characterize the effects of nutrient enrichment on the macrophyte community changes in the Everglades ecosystem. Macrophyte species distribution and frequency examined at 51 sites located in the Water Conservation Area (WCA‐2A) revealed distinct trends in species changes with P enrichment. Marshes in the unenriched and enriched areas were dominated by Cladium jamaicense and Typha domingensis, respectively. Open water areas were characterized by Eleocharis sp., Utricularia sp., Chara zeylanica, and Nymphaea odorata in the unenriched areas and by floating plants and Polygonum sp. in the enriched areas. We compared the macrophyte species distribution with the soil P contour map of WCA‐2A and derived six major categories of P enrichment (labeled 0–5) that may be used to adequately describe macrophyte species distribution in the WCA‐2A. Soil and surface water P values that correspond to the different P‐enrichment categories and the number of macrophyte species in each category have been estimated. Examination of the relative abundance of the macrophyte species in the six P‐enrichment categories showed a decline in characteristic slough macrophyte species with P enrichment. Increase in P status of the system was also accompanied by the advent and gradual establishment of macrophytes such as Mikania scandens, Sarcostemma clausum, Polygonum sp., Acrostichum danaeifolium, and a variety of floating plants. Characteristic slough macrophyte species such as Utricularia purpurea, Eleocharis elongata, and Eleocharis cellulosa serve as indicators of the unenriched P conditions.

Controls on emergent macrophyte composition, abundance, and productivity in freshwater Everglades wetland communities

The relationships between tissue nutrient content, species-specific productivity, and species abundance were investigated in seven emergent wetland species to determine how important a functional role phosphorus availability plays in controlling specific composition, abundance, and productivity in two naturally occurring Everglades wetland communities (sawgrass and wet prairie). Evidence from our tissue nutrient data suggest that the dominant taxa in each of these communities (Cladium jamaicense in the sawgrass community andEleocharis spp. in the wet prairie community) are strongly limited by phosphorus and that the availability of this nutrient is important in controlling the productivity of each of these taxa.Cladium jamaicense had a significantly higher molar N:P ratio than either of the two other species, which were found to co-exist in the sawgrass community, suggesting that this species has extremely low requirements for phosphorus and, consequently, may be able to most effectively use phosphorus under conditions of low availability. Nutrient availability also seemed to be important toPeltandra virginica, although it seems that this species may be limited by nitrogen as opposed to phosphorus. Unlike bothC. jamaicense andP. virginica, nutrient availability (either nitrogen or phosphorus) was insufficient to explain patterns of productivity or abundance forP. cordata, suggesting that some other environmental factor is more important for this species. In the wet prairie community, bothEleocharis spp. and the second most abundant species,Sagittaria lancifolia, had relationships that suggested that the productivity or abundance of both of these species is regulated by phosphorus availability. In contrast,Panicum hemitomon, an important Everglades plant, did not show either productivity or abundance patterns that could be adequately explained in terms of nutrient availability. It seems more likely that, similar toP. cordata in the sawgrass community, some other environmental variable is more important than phosphorus availability—although the high N:P ratios inP. hemitomon leaf tissue do suggest that this species is phosphorus-limited. Furthermore, leaf tissue N:P data also suggested thatHymenocallis palmeri may be limited entirely by nitrogen, rather than phosphorus.

Turnover of Detrital Organic Carbon in a Nutrient‐Impacted Everglades Marsh

AbstractPhosphorus loading to the Everglades from nearby agricultural areas has become a major concern, and is considered to be a significant factor in the encroachment of cattail (Typha domingensis Pers.) and other rapidly growing vegetation into endemic sawgrass (Cladium jamaicense Crantz) marsh. The objectives of this research were to evaluate the variability in turnover of organic C in plant and soil detrital pools along a P enrichment gradient in an Everglades marsh and to identify substrate characteristics and environmental factors controlling C turnover. Potential rates of C mineralization in plant litter and peat were determined by measuring aerobic and anaerobic microbial respiration under controlled conditions in laboratory incubations. Potential C mineralization decreased with depth and, consequently, substrate age, in the plant‐soil profile. Within individual detrital pools [standing dead plant material, soil litter layer, surface peat (0–10 cm depth) and subsurface peat (10–30 cm depth)], potential C mineralization decreased down gradient from the source of nutrient loading to WCA‐2A. Overall, 91% of the variability in aerobic C mineralization in peat and plant litter was accounted for by substrate P concentration and lignocellulose composition. Anaerobic C mineralization rates were consistently about one‐third of aerobic rates. Results indicated that organic C turnover in detrital pools in WCA‐2A is significantly affected by accelerated P loading, but is also controlled by O2 availability and substrate C quality.

Effects of various treatments on the germination of sawgrass,Cladium jamaicense Crantz, seeds

The objective of this research was to test the effectiveness of several treatments at raising germination percentages of sawgrass (Cladium jamaicense) seeds. Sawgrass seed lots from two years (1991 and 1995) were tested in two separate germination experiments that were run from 1994 to 1995 and 1995 to 1996. Treatments aimed at breaking dormancy were abrasion with sand paper, steeping in hot water, dry heating, soaking in nitric acid or sodium hypochlorite, cold, moist stratification (for a duration of 3 days or 1 month), and supplements of exogenous chemicals (gibberellic acid or potassium nitrate). A combination treatment of wet heat followed by soaking in gibberellic acid was tested. In the 1994–1995 experiment, no treatment was effective at increasing germination over that of untreated seeds (P>0.05). Treatments with dry heat, abrasion, the combination treatment, and the water control significantly reduced germination. In contrast, in the 1995–1996 experiment, treatment with sodium hypochlorite (bleach) significantly increased sawgrass germination in comparison with untreated seeds. Cold, moist stratification for one month significantly increased germination over that found in the water control. The highest germination of nearly 80% was achieved in seeds that were treated with bleach. The results of this experiment suggest that the disinfectant properties of bleach may be one mechanism through which sawgrass germination is enhanced.

Factors influencing cattail abundance in the northern Everglades

Since the early 1900s, the Everglades have been influenced by anthropogenic actions including altered hydrology and increased nutrient loading. In the northern Everglades an apparent effect of these disturbances has been the development and proliferation of dense cattail ( Typha spp. ) stands in areas previously dominated by sawgrass ( Cladium jamaicense Crantz) and sloughs. Cattail cover, soil nutrient concentrations, topography and fire history were determined for the Holey Land and Rotenberger Wildlife Management Areas, located in the northern Everglades. These data were analyzed using multiple regression to assess the relative influence of fire, hydrology and soil nutrients on cattail abundance. Holey Land and Rotenberger were overdrained over recent decades which resulted in soil compaction and nutrient accumulation, illustrated by increased soil bulk densities and elevated nutrient storage. Average bulk densities were 0.13 g cm −3 for Holey Land and 0.22 g cm −3 for Rotenberger. Average total P (TP) stored in the surface 10 cm of soil in Holey Land and Rotenberger were 7 and 13 g m −2, respectively. In contrast, Everglades soils uninfluenced by nutrient enrichment and with less severe overdrainage have bulk densities of 0.07 g cm −3 and TP storage of 4 g m −2. Typically, elevated soil P concentrations have been considered a primary factor influencing cattail growth and distribution in the Everglades. With the apparent absence of P limitation in Holey Land and Rotenberger, cattail abundance was influenced by either fire or hydrology. Forty-six percent of the variation of cattail cover in Holey Land was explained by elevation, indicating that increased water depth and duration of flooding have a significant impact on cattail expansion. In Rotenberger, fire was the most influential factor, explaining 57% of the variation in cattail cover. Hydrology was the second most important factor limiting cattail abundance.