The Relationship Between Relative Growth Rate and Sensitivity to Nutrient Stress in Twenty-Eight Species of Emergent Macrophytes

Abstract

(1) Stress sensitivity is defined as the decrease in the relative growth rate of a species relative to a decline in resource supply. This definition is used to test the hypothesis of a trade-off between maximum relative growth rates and sensitivity to stress. (2) The data used to test this hypothesis were collected from twenty-eight species of emergent macrophytes, occurring in north-eastern North America. Seedlings of these species were grown from seed in washed sand in a glasshouse in two nutrient conditions: full strength Hoagland's solution and one-tenth strength Hoagland's solution. Relative growth rates were determined from seedlings aged ten to thirty days old. (3) There was no correlation between relative growth rate in the full strength Hoagland's solution and relative growth rate in the one-tenth Hoagland's solution (r = 029, P> 0 1). (4) This resulted in a strong positive correlation between relative growth rate of these species in full strength Hoagland's solution and their sensitivity to decreasing nutrient supply (stress) (r=080, P<0 001), indicating that those species whose relative growth rate was highest in the more fertile conditions had their relative growth rate most depressed in the less fertile conditions. (5) This relationship held even on a proportional basis, such that the proportional decrease in relative growth rate was correlated with sensitivity to nutrient stress (r = 0 55, P<0 1).