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

<p>Abstract</p> <p>Background</p> <p>Cattail (<it>Typha domingensis</it>) has been spreading in phosphorus (P) enriched areas of the oligotrophic Florida Everglades at the expense of sawgrass (<it>Cladium mariscus </it>spp. <it>jamaicense</it>). Abundant evidence in the literature explains how the opportunistic features of <it>Typha </it>might lead to a complete dominance in P-enriched areas. Less clear is how <it>Typha </it>can grow and acquire P at extremely low P levels, which prevail in the unimpacted areas of the Everglades.</p> <p>Results</p> <p>Apparent P uptake kinetics were measured for intact plants of <it>Cladium </it>and <it>Typha </it>acclimated to low and high P at two levels of oxygen in hydroponic culture. The saturated rate of P uptake was higher in <it>Typha </it>than in <it>Cladium </it>and higher in low-P acclimated plants than in high-P acclimated plants. The affinity for P uptake was two-fold higher in <it>Typha </it>than in <it>Cladium</it>, and two- to three-fold higher for low-P acclimated plants compared to high-P acclimated plants. As <it>Cladium </it>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, <it>Typha </it>increased biomass allocation to roots more than <it>Cladium</it>. Both species also adjusted their P uptake kinetics, but <it>Typha </it>more so than <it>Cladium</it>. The adjustment of the P uptake system and increased biomass allocation to roots resulted in a five-fold higher uptake per plant for <it>Cladium </it>and a ten-fold higher uptake for <it>Typha</it>.</p> <p>Conclusions</p> <p>Both <it>Cladium </it>and <it>Typha </it>adjust P uptake kinetics in relation to plant demand when P availability is high. When P concentrations are low, however, <it>Typha </it>adjusts P uptake kinetics and also increases allocation to roots more so than <it>Cladium</it>, thereby improving both efficiency and capacity of P uptake. <it>Cladium </it>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 <it>Cladium </it>and <it>Typha </it>have qualitatively similar strategies to improve P-uptake efficiency and capacity under low P-conditions, <it>Typha </it>shows a quantitatively greater response, possibly due to a lesser expression of these mechanisms than <it>Cladium</it>. This difference between the two species helps to explain why an opportunistic species such as <it>Typha </it>is able to grow side by side with <it>Cladium </it>in the P-deficient Everglades.</p

Factors and mechanisms influencing seed germination in a wetland plant sawgrass

Abstract Sawgrass (Cladium jamaicense) is the predominant plant and vegetation community in the Florida Everglades. Germination of sawgrass seeds in the laboratory or nursery has been difficult and problematic, yet little is known about the physiological mechanistic regulation of the sawgrass seed germination process. In the present study, we examined the factors and mechanisms that influence sawgrass seed germination. We found that removal of seed husk and bracts, pre-soaking with bleach (hypochlorite), breaking the seed coat, or combinations of these treatments promoted the rate and success of germination, whereas presence of seedencasing structures or treatment with husk/bract extract inhibited germination. We further detected the presence of abscisic acid (ABA) in the husk and bract. Experiments with ABA and gibberellin biosynthesis inhibitors fluridone and tetcyclacis suggested that ABA already presented in the pre-imbibed seeds, and not derived through post-dormancy de novo synthesis, contributed to the inhibition of seed germination. Examination of bleach and mechanical treatments indicated the physical barrier presented by the seed-encasing structures provided additional mechanism for the long-term delay of seed germination. Based on the results of this study and others, we discussed the implications of sawgrass seed dormancy and germination in relation to its natural habitat and proposed a hypothesis that the protracted seed dormancy in sawgrass offered an adaptive advantage in the pre-anthropogenic Everglades environment, but may become a liability in the current man-managed Everglades water system

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 mg P L 21 ) and Eh level (2150, þ150 and þ600 mV). Plants were grown hydroponically in a factorial experiment using titanium (Ti 3þ ) 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 mg P L 21 / þ 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

The ecological–societal underpinnings of Everglades restoration

The biotic integrity of the Florida Everglades, a wetland of immense international importance, is threatened as a result of decades of human manipulation for drainage and development. Past management of the system only exacerbated the problems associated with nutrient enrichment and disruption of regional hydrology. The Comprehensive Everglades Restoration Plan (CERP) now being implemented by Federal and State governments is an attempt to strike a balance between the needs of the environment with the complex management of water and the seemingly unbridled economic growth of southern Florida. CERP is expected to reverse negative environmental trends by “getting the water right”, but successful Everglades restoration will require both geochemical and hydrologic intervention on a massive scale. This will produce ecological trade-offs and will require new and innovative scientific measures to (1) reduce total phosphorus concentrations within the remaining marsh to 10 μg/L or lower; (2) quantify and link ecological benefits to the restoration of depths, hydroperiods, and flow velocities; and (3) compensate for ecological, economic, and hydrologic uncertainties in the CERP through adaptive management