Appropriation of nitrogen by the invasive cattail Typha × glauca

Abstract

A 15N-addition mesocosm experiment was used to study competition for nitrogen (N) between the aggressive cattail species Typha×glauca (T. latifolia×T. angustifolia) Godr. (hybrid cattail) and a suite of native plant species often found in marshes Typha invades. Plant uptake of 15N released from labeled Typha and native-species litter was then measured in a pot experiment with new cohorts of two native plant species (Juncus balticus Willd. and Schoenoplectus acutus Muhlenberg ex Bigelow) grown with and without Typha. In both experiments, species differed in their above- and belowground uptake of 15N, with Typha outperforming the other species (1.7–5.0-times greater mean uptake, P=<0.0001–0.007). Typha then held on more strongly to the N it acquired: newly grown native plants in the pot experiment acquired more 15N from native litter than from Typha litter (1.4–12.0-times greater mean uptake, P=0.0006–0.017). In contrast, Typha showed no differences in N uptake by litter type (P=0.16–0.54). There were no main effects of live Typha on native-plant N uptake (P=0.64–0.86), but there were modest interactions between Typha presence and litter type (P=0.030–0.091). Where native plants and Typha co-occurred, native species matched Typha in recovering 15N from native litter (P=0.17–0.33) but recovered 90–96% less 15N from Typha litter (P=0.020–0.021). Typha's higher overall N recovery was due to both greater biomass production and uptake efficiency (15N per unit dry weight). Typha's greater N uptake and retention, repeated over multiple cycles of senescence and new growth, should lead to an increasing appropriation of N away from native species and into living and dead Typha biomass.