Canopy structure, photosynthetic capacity and nitrogen distribution in adjacent mixed and monospecific stands of Phragmites australis and Typha latifolia

Shifts in canopy structure associated with nonnative plant invasions may interact with species-specific patterns of canopy resource allocation to reinforce the invasion process. We documented differences in canopy light availability and canopy resource allocation in adjacent monospecific and mixed stands of Phragmites australis and Typha spp. in a Great Lakes coastal wetland presently undergoing Phragmites invasion to better understand how light availability influences leaf nitrogen content (N-mass) and photosynthetic capacity (A(max)) in these species. Due to their horizontally oriented leaves, light attenuates more rapidly in monospecific stands of Phragmites than in monospecific stands of Typha, where leaves are more vertically-oriented. Whereas Typha canopies followed our prediction that patterns of N-mass and A(max) should closely parallel patterns of canopy light availability, N-mass and A(max) were consistent throughout Phragmites' canopies. Moreover, we observed overall greater N-mass and lower photosynthetic nitrogen use efficiency in leaves of Phragmites than in leaves of Typha. Improved understanding of the link between N-mass and A(max) in these canopies should improve our understanding of carbon and nitrogen cycling consequences of Phragmites invasion in wetland ecosystems.