ShiLi Miao

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

The germination requirements of Cladium jamaicenseCrantz and Typha domingensisPers. were studied under controlled conditions in the laboratory. Treatments included six temperature regimes, (constant temperatures of 15 20, 25, 30C, and two fluctuating day : night temperature regimes of 25 : 10C and 30 : 20C), two light levels (14 : 10 h light : dark photoperiod and 24 h dark environment), two substrates (peat and water) and two O2 levels (atmospheric and low (4.34%) O2 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 jamaicenseonly germinated with fluctuating temperatures whereas T. domingensisgerminated at all temperature regimes. Light was required for T. domingensisseeds to germinate, whereas C. jamaicensecould 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. domingensisat 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 domingensisproduces a large number of small seeds, which do not germinate when covered by sediment. In contrast, C. jamaicenseproduces fewer and larger

Nutrient and growth responses of cattail (Typha domingensis) to redox intensity and phosphate availability

BACKGROUND AND AIMS In the Florida Everglades, the expansion of cattail (Typha domingensis) into areas once dominated by sawgrass (Cladium jamaicense) has been attributed to altered hydrology and phosphorus (P) enrichment. The objective of this study was to quantify the interactive effects of P availability and soil redox potential (Eh) on the growth and nutrient responses of Typha, which may help to explain its expansion. METHODS The study examined the growth and nutrient responses of Typha to the interactive effects of P availability (10, 80 and 500 microg P L(-1)) and Eh level (-150, +150 and +600 mV). Plants were grown hydroponically in a factorial experiment using titanium (Ti(3+)) citrate as a redox buffer. KEY RESULTS Relative growth rate, elongation, root-supported tissue/root ratio, leaf length, lateral root length and biomass, as well as tissue nutrient concentrations, were all adversely affected by low Eh conditions. P availability compensated for the negative effect of low Eh for all these variables except that low P stimulated root length and nutrient use efficiency. The most growth-promoting treatment combination was 500 microg P L(-1)/ + 600 mV. CONCLUSIONS These results, plus previous data on Cladium responses to P/Eh combinations, document that high P availability and low Eh should benefit Typha more than Cladium as the growth and tissue nutrients of the former species responded more to excess P, even under highly reduced conditions. Therefore, the interactive effects of P enrichment and Eh appear to be linked to the expansion of Typha in the Everglades Water Conservation Area 2A, where both low Eh and enhanced phosphate availability have co-occurred during recent decades.

Growth and nutrient responses of Eloecharis cellulosa (Cyperaceae) to phosphate level and redox intensity.

Phosphorus (P) availability limits plant growth in many ecosystems. The ability of plants to explore for soil P is often impaired by nonresource stressors. Understanding the effects of these stressors on P acquisition in oligotrophic environments is critical in predicting species dominance. Growth and nutrient responses of Eleocharis cellulosa to redox intensity and phosphate level were evaluated under three redox potentials (Eh) and three phosphate (PO(4)) levels (P). Although low Eh (-150 mV) decreased root length at low P, Eh did not affect shoot height, relative growth rate (RGR), shoot elongation, photosynthesis, or biomass of E. cellulosa. Low PO(4) (10 μg P · L(-1)) strongly inhibited growth. Shoot height, RGR, elongation, photosynthesis, and biomass were lower at 10 μg P · L(-1) than at 80 or 500 μg P · L(-1). None of the growth variables, except the ratio of root-supported biomass to root biomass, significantly differed between the 80 and 500 μg P · L(-1) treatments. At low P, plants allocated relatively more biomass to roots than to shoots, compared to the medium and high P levels. Eleocharis cellulosa is well adapted to flooded conditions that lower soil Eh, and elevated PO(4) levels further promote its growth potential.

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.

Interactive effects of redox intensity and phosphate availability on growth and nutrient relations of Cladium jamaicense (Cyperaceae)

Expansion of Typha domingensis into areas previously dominated by Cladium jamaicense in the Florida Everglades has been linked to anthropogenic phosphorus (P) enrichment and increased hydroperiod. The principal stress factor for plants in flooded soils is biochemical reduction, the intensity of which is measured as redox potential (Eh). The objective of this study was to assess the growth response of C. jamaicense to Eh (-150, +150, and +600 mV) and P availability (10, 80, and 500 μg P/L). Plants were grown hydroponically in a factorial experiment using titanium (Ti(3+)) citrate as an Eh buffer. Treatment effects on growth, biomass partitioning, and tissue nutrients were recorded. Growth approximately doubled in response to a 50-fold increase in P availability. Low redox significantly reduced growth and tissue P concentration. While plant P concentrations increased 20-fold between the 10 and 500 μg P/L treatments, P concentrations were 50-100% higher at +600 mV than at -150 mV within each phosphate level. At high Eh, C. jamaicense appears well adapted to low nutrient environments because of its low P requirement and high retention of acquired P. However, at low Eh the ability to acquire or conserve acquired P decreases and as a consequence, higher phosphate levels are required to sustain growth. Findings of this study indicate that young C. jamaicense exhibits low tolerance to strongly reducing conditions when phosphate is scarce.

Immediate ecological impacts of a prescribed fire on a cattail-dominated wetland in Florida Everglades

The effects of fire on nutrient release in wetlands prior to, during and afterwards are notably rare. We initiated a long-term and large-scale ecosystem study, driven by a large restoration program, to assess ecological effects of repeated fires on a nutrient-enriched, cattail-dominated wetland in the Florida Everglades. Here, we report the immediate and short-term (30 days) impacts of the first prescribed fire focusing on a central question of whether the fire affected surface-and pore-water nutrient concentrations and forms. Specifically, we addressed several questions: 1) how fast could the impacts be detected, 2) what were the magnitude and duration of the impacts, and 3) were there any downstream effects detected and if so, how far downstream was the impact observed? The results showed that post-fire increases of average surface water total phosphorus (TP) concentrations over 10 days were 128 %, 119 %, and 135 % for within burned plot, 25 m downstream, and 100 m downstream, respectively, relative to the upstream control (82 +/- 11 mu g L(-1)). A post-fire surface water pH peak (8.4) was observed as soon as 15 minutes after the fire reached within burned plot, and the increase in pH lasted at least three weeks. A significant increase (400 %) in the daily peak dissolved oxygen was detected by the third week post-fire. Daily maximum water temperature increased 2-4 degrees C post-fire and this increase lasted the duration of the 30-day sampling period. Average periphyton TP concentrations from samples collected within burned plot were 3495 +/- 320 mg kg(-1) one month post-fire, but decreased to 1730 +/- 219 mg kg(-1) three months post-fire. Cattail seed germination decreased (41 %) from pre- to post-fire, while seed germination of sawgrass and other species increased (97 % and 12 %, respectively). Overall, whether these short-term responses have sustained effects and how they will shape other entities of the ecosystem in the long-term are currently being investigated and will be assessed in the near future.

Can differences in phosphorus uptake kinetics explain the distribution of cattail and sawgrass in the Florida Everglades

BackgroundCattail (Typha domingensis) has been spreading in phosphorus (P) enriched areas of the oligotrophic Florida Everglades at the expense of sawgrass (Cladium mariscus spp. jamaicense). Abundant evidence in the literature explains how the opportunistic features of Typha might lead to a complete dominance in P-enriched areas. Less clear is how Typha can grow and acquire P at extremely low P levels, which prevail in the unimpacted areas of the Everglades.ResultsApparent P uptake kinetics were measured for intact plants of Cladium and Typha acclimated to low and high P at two levels of oxygen in hydroponic culture. The saturated rate of P uptake was higher in Typha than in Cladium and higher in low-P acclimated plants than in high-P acclimated plants. The affinity for P uptake was two-fold higher in Typha than in Cladium, and two- to three-fold higher for low-P acclimated plants compared to high-P acclimated plants. As Cladium had a greater proportion of its biomass allocated to roots, the overall uptake capacity of the two species at high P did not differ. At low P availability, Typha increased biomass allocation to roots more than Cladium. Both species also adjusted their P uptake kinetics, but Typha more so than Cladium. The adjustment of the P uptake system and increased biomass allocation to roots resulted in a five-fold higher uptake per plant for Cladium and a ten-fold higher uptake for Typha.ConclusionsBoth Cladium and Typha adjust P uptake kinetics in relation to plant demand when P availability is high. When P concentrations are low, however, Typha adjusts P uptake kinetics and also increases allocation to roots more so than Cladium, thereby improving both efficiency and capacity of P uptake. Cladium has less need to adjust P uptake kinetics because it is already efficient at acquiring P from peat soils (e.g., through secretion of phosphatases, symbiosis with arbuscular mycorrhizal fungi, nutrient conservation growth traits). Thus, although Cladium and Typha have qualitatively similar strategies to improve P-uptake efficiency and capacity under low P-conditions, Typha shows a quantitatively greater response, possibly due to a lesser expression of these mechanisms than Cladium. This difference between the two species helps to explain why an opportunistic species such as Typha is able to grow side by side with Cladium in the P-deficient Everglades.

Effects of a prescribed fire on dissolved inorganic carbon dynamics in a nutrient-enriched Everglades wetland

The purpose of this study was to assess the short-term response of dissolved inorganic carbon (DIC) chemistry to a prescribed fire in a nutrient-enriched area of the Everglades. Surface water samples were analyzed for water temperature, pH, total carbon (TC) and DIC concentrations in the bum area, in addition to one upstream and two downstream stations, pre- and post-fire for a period of 14 weeks. Dissolved free carbon dioxide (CO 2 ), the partial pressure of CO 2 (pCO 2 ) and CO 2 flux between surface water and the atmosphere were calculated. Although a large amount of unburned litter remained in the burned area and an immediate increase in the DIC concentration was observed post-fire, the average DIC concentration at the bum area was only slightly higher than the upstream station and lower than the two downstream stations. Similarly, CO 2 concentrations and pCO 2 at the burn area were lower than those of the three control stations. The low CO 2 and pCO 2 immediately post-fire were likely attributed to the elevated pH due to the addition of basic ash. However, the continuously low CO 2 and pCO 2 were the combined results of high pH and increased CO 2 sequestration by the growth of periphyton triggered by increased availability of light and growth space. These factors also explain why the DIC concentration at the burn area did not show a dramatic increase after the fire. Overall, our results suggest that despite decreases in pCO 2 post-bum, this wetland continues to act as a net source of CO 2 to the atmosphere.

Integrating Multiple Spatial Controls and Temporal Sampling Schemes To Explore Short- and Long-Term Ecosystem Response to Fire in an Everglades Wetland

Ecosystem and landscape studies are often faced with less than ideal, large-scale scenarios which are challenged by traditional approaches to experimental design and analysis, primarily because these studies can not be adequately replicated and are confronted by multiple spatial and temporal scales of variation. Variations in parameter and response time further complicate experimental design and data analysis. Rather than struggle with controlling or minimizing the influence of spatial and temporal variation via statistically required replication, we employed BACI and BACIPS designs and applied multiple spatial-scale controls and unbalanced temporal sampling schemes to account for the spatial and temporal structure of the studied system. This multiple-scale design allowed us to assess both pulsed and sustained responses of critical ecosystem processes to a prescribed fire in a nutrient-enriched wetland. A series of regression approaches and confidence intervals were employed to estimate onset, duration, and magnitude of post-fire ecosystem responses. This chapter describes a powerful approach for studying ecosystem disturbance including issue identification, experimental design, data analysis and interpretation, and management recommendations.

Impacts of fire and phosphorus on sawgrass and cattails in an altered landscape of the Florida Everglades

IntroductionAlthough fire as a critical ecological process shapes the Florida Everglades landscape, researchers lack landscape-based approach for fire management. The interactive effect of fire, nutrients, water depth, and invasive cattails (Typha spp.) on vegetation communities is of special concern for ecosystem restoration. In particular, questions concerning the effect of fire on nutrient release and, by extension, the potential thereof to stimulate sawgrass (Cladium jamaicense Crantz) re-growth and cattail expansion under varying hydrological conditions are of immediate relevance to ecologists and land managers who work to restore the Everglades.MethodsIn late April of 1999, a 42,875 ha surface fire, including a 100 ha peat fire, burned the northern section of Water Conservation Area 3A (WCA-3A) in the Everglades. In this study, total phosphorus (TP) in soil, surface water, pore-water, and vegetation was sampled at non-burned, surface-burned and peat-burned areas within one and five months after the burn. Four years after the initial fire, field data were collected in a large scale survey to analyze how the 1999 fire affected cattail distribution in the altered landscape of high soil TP and cattail habitats. Existing GIS maps were utilized to select field sampling locations and to provide additional information for the analysis.ResultsThe analyses showed that five months after the fire, sawgrass biomass re-growth was about 5 times higher in burned areas (611 ± 47 g/m2) than in non-burned areas (102 ± 18 g/m2). Sawgrass re-growth in water depths less than 30 cm was 4.9 ± 0.4 g/m2/day while sawgrass re-growth in water depths deeper than 60 cm decreased to 0.5 ± 0.3 g/m2/day. Cattail biomass re-growth in peat-burned areas was as high as 1,079 ± 38 g/m2. The data also showed that post-fire cattail expansion could be related to cattail stands existing before the fire. Furthermore, post-fire cattail appeared more significant expansion in the areas with soil TP above 900 mg/kg than in that with soil TP below 900 mg/kg.ConclusionsThe data showed that fire within altered landscapes (e.g. high soil TP and/or cattail) of the Everglades could stimulate the re-growth and expansion of cattails, and post-fire re-growth of sawgrass could be severely impeded by deep water after a surface-burn. This research indicates that fire continues to be an effective ecological process for maintaining the Everglades; therefore, ecologists and land managers may have to reevaluate the future management of natural fire with regard to its dynamic relationship with high soil TP and cattail expansion in the altered Everglades landscape.