The response of an emergent sedge Bolboschoenus medianus to salinity and nutrients

The potential for nutrient load (30, 100 and 350 g N m^?2 per year) to alter plant performance under saline conditions (control, 4.5, 9 and 13 dS m^?1) was examined in the sedge Bolboschoenus medianus. Relative growth rates (RGR) across nutrient loadings ranged from 30.2 to 41.8 mg g^?1 per day in controls and were reduced to 20.9–28.5 mg g^?1 per day by salinities of 13 dS m^?1. Whilst higher nutrient loads generally increased RGR, the response was smaller at higher salinities. Responses to salinity and nutrient load were specific. Nutrient load increased the RGR via increases in the leaf area ratio (LAR). The LAR ranged from 1.9 to 2.1 m² kg^?1 across salinity treatments at 30 g N m^?2 per year, and increased to 2.5–2.8 m² kg^?1 at 350 g N m^?2 per year. Salinity reduced the RGR via a reduction in the net assimilation rate (NAR). The NAR in control plants ranged from 14.7 to 16 g m^?2 per day across nutrient loadings and decreased to 11–12 g m^?2 per day at 13 dS m^?1. Carbon isotope discrimination of leaves decreased by 2–3‰ in response to 13 dS m^?1 at the lower nutrient loadings. A prominent response of B. medianus to salinity was a change in biomass allocation from culms to tubers. In contrast, the response to nutrient load was characterised by a shift in biomass allocation from roots to leaves.