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

The potential for nutrient load (30, 100 and 350 g Nm(-2) per year) to afte r 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 1 3 dS m-l 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 ar ea ratio (LAR). The LAR ranged from 1.9 to 2.1 m(2) kg(-1) across salinity treatments at 30 g N m(-2) per year, and increased to 2.5-2.8 m(2) kg(-1) a t 350 g N m(-2) per year. Salinity reduced the RGR via a reduction in the n et assimilation rate (NAR). The NAR in control plants ranged from 14.7 to 1 6g m(-2) per day across nutrient loadings and decreased to 11-12g m(-2) per day at 13 dS m(-1). Carbon isotope discrimination of leaves decreased by 2 -3 parts per thousand in response to 13 dS m(-1) at the lower nutrient load ings. A prominent response of B. medianus to salinity was a change in bioma ss allocation from culms to tubers. In contrast, the response to nutrient l oad was characterised by a shift in biomass allocation from roots to leaves . (C) 2001 Elsevier Science B.V. All rights reserved.