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.

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Premise of research. Formerly sparsely distributed southern cattail (Typha domingensis) is now rapidly replacing the historically predominant sawgrass (Cladium jamaicense) in Florida Everglades wetlands. Previous studies have attributed anthropogenic phosphorus (P) enrichment as a causal factor. We investigated various traits of known importance to P acquisition and use in cattail and sawgrass, in order to determine the underlying mechanisms driving the sawgrass-cattail habitat shift.Methodology. An integration of morphological, physiological, biochemical, and molecular approaches were used to examine growth, root structure, photosynthesis, enzyme activities, and gene expression in plants grown under different P conditions.Pivotal results. Cattail and sawgrass exhibited distinct patterns of P responses between roots and shoots. While cattail displayed plasticity in shoots and inflexibility in roots, sawgrass demonstrated the opposite pattern, exhibiting a remarkable capacity for modulating its root system architecture, acid phosphatase activity, and phosphate transporter abundance. Likely advantageous under P impoverishment for sawgrass in the historic Everglades undisturbed by man, these adaptations are nullified under current anthropogenic P enrichment, thus opening the door for competition from cattail. In response to high P availability, cattail exhibited enhanced protein synthesis, photosynthesis, and growth in its plastic shoots, empowering its spatial expansion at the expense of sawgrass.Conclusions. The species-specific patterns of root/shoot-disparate plasticity may be an important mechanism underlying the spatial redistribution of cattail and sawgrass in the anthropogenic resource-altered environment. High plasticity in shoots in response to environmental nutrient enrichment is likely a common trait shared by invasive-prone plants.

In areas of the Florida Everglades, USA, a massive replacement of the historically predominant sawgrass by native cattail is occurring. Phosphorus enrichment due to runoff and hydrological engineering is considered a major environmental cause. As part of our investigation into the genetic and molecular mechanisms underlying this habitat shift, we examined the possible involvement of arbuscular mycorrhizal (AM) symbiosis in sawgrass and cattail. Laboratory experiments determined that sawgrass, but not cattail, was susceptible to fungal inoculation and formed AM under low phosphate (Pi) conditions. Collection of plants from four representative sites in the Everglades revealed that while all sawgrass plants formed root AM associations, no AM was detected in cattail. We identified a phosphate transporter gene of sawgrass, CjPT4, that was preferentially expressed in roots of fungal inoculated and AM plants. In contrast, cattail PT genes were steadily expressed regardless of Pi levels. Our studies demonstrate a strong possibility that ability to form AM symbiosis is a key genetic distinction between sawgrass and cattail in their adaptive response to the changing phosphorus environment. We propose a mechanistic explanation based on AM symbiosis for the distribution and competition of these two plants in the pre-industrial Pi-deficient and modern Pi-enriched Florida Everglades ecosystems.