Involvement of Arbuscular Mycorrhizal Symbiosis in the Distribution of Sawgrass and Cattail in Florida Everglades

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.