Imperata cylindrica, an alien invasive grass, maintains control over nitrogen availability in an establishing pine forest

Abstract

In a field experiment in Florida, USA, 15N-labeled Ammonium Sulfate was used to compare how Pinus taeda seedlings take up and use N in the presence of I. cylindrica and native vegetation using three treatments: 1) vegetation free 2) native competition, and 3) I. cylindrica competition. Imperata cylindrica competition led to smaller pine seedlings with significantly less N content in the pine foliage and roots than those in the native treatment. Competition from I. cylindrica for N contributed to the pine seedlings taking up a greater percentage of the applied fertilizer than the seedlings competing with native vegetation; however, because of their reduced growth they were less efficient in utilizing the fertilizer N. The belowground biomass of I. cylindrica on average was seven times higher than the native species. Despite its lower N concentration in foliage and roots, it retained significantly more N per hectare compared to the native vegetation. While the native species retained more N aboveground, I. cylindrica held significantly more belowground, thus invasion by this grass would lead to a shift of N pools from above to belowground. The fact that we were able to account for 81.5% of the applied fertilizer in the I. cylindrica treatment compared to 62.2% in the native treatment suggests that I. cylindrica tightly retains most of the available N on site making it a particularly good invader.