Justicia americana exhibits stem density–aboveground biomass relationships and variability in elemental composition and isotopic signature across tissue types and land use gradients

Abstract

Riverine macrophytes are increasingly understood to influence both the physical and chemical dynamics of rivers by creating biogeochemical hotspots and stabilizing benthic sediments. They contribute carbon and nutrients to both aquatic and adjacent terrestrial ecosystems through senescence and herbivory. Here, we report the relationships between Justicia americana biomass, stem length, and stem density, and % carbon (%C), % nitrogen (%N), C:N, δ15N, and δ13C relationships between tissues types (roots, stems, and leaves). Additionally, we report the effects of land use on the plant's tissue. We found that (1) J. americana stem density and dry biomass were positively correlated ( P < 0.001); (2) δ13C and %N were significantly different in leaf and root tissue; (3) δ13C and δ15N were both positively correlated across tissue types; (4) Leaf C:N was less than ½ of root and stem tissue; (5) %C in leaf tissue was positively correlated ( P < 0.05) with forest cover and negatively correlated with urbanization and watershed area; and (6) provide evidence that J. americana utilizes a C3 photosynthetic pathway. Overall, this study provides novel insight into the ecology of J. americana by elucidating the nutritional quality of different plant tissues and stoichiometric changes in the plant in response to land use.