The effects of periphyton density and current on rates of nutrient transport from the water column through periphyton were measured with periphyton on glass-fiber filters. The flux of NO, and Si was inversely related to periphyton density, but Cl flux was affected only by the highest periphyton densities. The relatively greater decreases in NO, and Si flux than in Cl flux with increases in periphyton density indicated that nutrient uptake by periphyton affected nutrient transport through periphyton. The negative effect of high-density periphyton on Cl transport indicated that the physical structure of periphyton interfered with flux through the microbial matrix. Current had a positive effect on flux of both NO, and Cl through periphyton. The positive effect of current on NO, flux through periphyton increased as periphyton density increased.

a b s t r a c tPhysiological integration among ramets of invasive plant species may support their colonization and spread in novel aquatic environments where growth-limiting resources are spatially heterogeneous. Under contrasting light conditions, we investigated how clonal integration influences growth, biomass allocation and morphology of Ludwigia hexapetala, an emergent floating-leaved macrophyte that is highly invasive in a range of wetland habitat types. In aquatic mesocosms, stolons of offspring ramets were either connected or severed from parent plants, with the pairs exposed to homogenous or heterogeneous combinations of sun or 85% shade. Morphological traits of all ramets were strongly influenced by light environment, and low light availability decreased plant growth, regardless of integration status. Allocation patterns varied with light regime; shaded plants increased allocation to leaf biomass while sun plants allocated more resources to belowground growth. Offspring ramets integrated with parents produced more biomass, suggesting a fitness advantage through integration. However, parent ramet performance declined with stoloniferous integration; integrated parents produced fewer ramets and allocated more resources to belowground biomass. For most response variables measured, there was no significant interactive effect between light treatment and integration, although parents growing in the shade attached to an offspring in the sun increased root mass ratio. The ability to establish and spread into new environments is a key trait of invasive plants, and physiological integration of resources may improve the establishment of juvenile ramets across variable light environments during early colonization. Physiological integration in patchy light environments may contribute to the invasiveness of L. hexapetala.Published by Elsevier B.V.

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