Rhizome growth and nutrient resorption: mechanisms underlying the replacement of two clonal species in Florida Everglades

Abstract

Spatial occupation and nutrient resorption (the process by which nutrients are recovered from senescing leaves to other plant tissue) are important mechanisms employed by plants to invade a new habitat and to recycle nutrients, respectively. Two clonal freshwater species with different life histories (sawgrass, Cladium jamaicense Crantz, and cattail, Typha domingensis Pers.) were studied to understand mechanisms underlying vegetation replacement in Florida Everglades. Seedlings of both species were planted in plastic pots holding approximately 1500 cm 3 of either phosphorus (P)-enriched (711 mg/kg) or P-unenriched (257 mg/kg) soil. Four holes in the bottom at the sides of each pot allowed rhizomes to spread outside the pot. The plants were placed in outdoor mesocosms with plenty of space for rhizomes to grow. For 1 year, water levels in the mesocosms were maintained between 15 and 25 cm with the same P treatment as the soil. Total biomass and ramet production of both species significantly increased in the enriched treatment, yet contrasting rhizome growth patterns were found between them. Although sawgrass genets produced a greater total biomass and number of ramets than cattails in the enriched treatment, cattail genets occupied a larger area. Morphological constraints in sawgrass limit its spatial expansion in P-enriched areas. Both species exhibited an extremely high P resorption efficiency, ranging from 69 to 82% for sawgrass and 61–71% for cattail. This finding supports that high-nutrient resorption from senescing leaves is characteristic for plant species with contrasting life histories. Thus, it is not appropriate to predict nutrient resorption efficiency of plants based on their nutrient concentrations in senesced leaves (i.e., proficiency values).