Temporary emersion enhances amphibious Isoetes production

Annual primary production of two amphibious quillworts was measured in two contrasting temporary environments in NE Spain: Isoetes echinospora growing in a high mountain semipermanent pool and Isoetes delilei growing in a Mediterranean pool. Leaf primary production showed a unimodal distribution with a peak in July for I. echinospora and in April for I. delilei. The population of I. echinospora produced 38.7 g DW m^–2 y^–1 (15.5 g C m^–2y^–1) of leaves the year of complete submersion, but leaf production increased to 49.3 g DW m^–2y^–1 (19.7 g C m^–2y^–1) the year with two months of emersion (27.4% increase). Leaf production of I. delilei also increased significantly after emersion (the pool dries out annually) and reached an annual leaf production of 676.7 g DW m^–2y^–1 (265.3 g C m^–2y^–1). I. delilei leaf production was 15 times higher than I. echinospora and much higher than the described range for submerged isoetids. The production increase of I. echinospora under temporal emersion together with the unusual high production of I. delilei thriving in temporary pools suggests that temporal emersion enhance amphibious isoetid production.