Plasticity of plant N uptake in two native species in response to invasive species.
Survival competition caused by limiting nutrients is often strong between invasive and native plant species. The effects of plant invasion on nutrient uptake in plant growth remain largely unclear. Clarifying how invasive plants affect N uptake by natives will provide a better understanding on mechanisms responsible for plant invasion. A 15N-labeling experiment was conducted using two common invasive species (Alternanthera philoxeroides (Mart.) Griseb. and Wedelia trilobata (L.) Hitchc.) and their native congeners (A. sessilis (L.) DC. and W. chinensis (Osbeck.) Merr.) to examine their growth and uptake of NH4+, NO3-, and glycine when grown in monocultures and mixed cultures. All plants were grown in a greenhouse for 70 days for labelling and biomass measurements. The main factor affecting N uptake by the four species was the form of N, rather than species identity. In all of the species, the most N was taken up in the form of NH4+, followed by NO3- and glycine. The two invasive species grew faster, with stable N-uptake patterns despite more moderate uptake rates of N than the native species. Native species were strongly affected by the invasive species. The presence of invasive species caused the N-uptake rates of the natives to be reduced, with altered N-uptake patterns, but did not substantially alter their growth rates. Native species reduced their N-uptake rates but increased N-use efficiency through altering N-uptake patterns in the presence of invasive plants. Such a flexible N-uptake pattern could be an important survival strategy for native plants in competition with invaders.