Emergent macrophytes in phosphorus limited marshes: do phosphorus usage strategies change after nutrient addition?

Two strategies for phosphorus (P) economy in P-limiting environment are conservation of use and enhanced acquisition. Using two wetland macrophytes as an example, we show how these strategies change when the P-limitation is removed. Phosphorus resorption and activities of root phosphatases were evaluated over 4 years in Eleocharis cellulosa Torr. and Typha domingensis Pers. from nutrient addition experiment (P, N, N&P, control) established in 15 P limited marshes of Belize. We hypothesized that after P addition both species will increase tissue P content and decrease P resorption efficiency and root phosphatase activity. Initially high phosphorus resorption efficiency, PRE, significantly decreased in Eleocharis 2 years after the first nutrient addition, while no significant decrease was recorded for Typha. Even more dramatic was 5- to 6-fold increase in P in senescent tissues of Eleocharis as compared to less than 2-fold increase in Typha. Root phosphatase activity was high for both species from control plots. After P addition, Eleocharis showed 35% to 70% decrease in enzyme activity correlated to availability of inorganic P in sediments. Eleocharis and Typha employ the conservation of use strategy when growing in P limited oligotrophic marshes. In addition, Eleocharis is also using the enhanced acquisition strategy. These strategies change when the P limitation is removed but the response varies between the two species and thus changes in the proportion of these two species in a community may result in differences in ecosystem processes such as decomposition.