PARENT SESSION
Poster Session #32: Plant Ecology I.
Wednesday, August 8, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Interspecific differences in plant growth response to nitrogen are associated with the response of ULR.

Taub, Daniel¹, ¹

ABSTRACT- A growth analysis approach was used to examine the plant traits underlying interspecific differences in growth response to nitrogen. Seedlings of 17 C₃ grass species were grown in sand culture in a glasshouse. High nitrogen plants were fertilized daily with 5 mM and low nitrogen plants with 0.05 mM NH₄NO₃. All other nutrients were present in amounts expected to be sufficient for optimal plant growth. Relative growth rate (RGR), specific leaf area (SLA), unit leaf rate (ULR) and leaf weight ratio (LWR) were determined for each species at each nitrogen level. The nitrogen response ratio of each parameter was determined as the value of the parameter at high nitrogen divided by the value at low nitrogen. Within species, growth response to nitrogen was largely associated with increased LWR at high vs. low nitrogen. For 14 of the 17 species, the LWR response ratio was greater than the response ratios for either ULR or SLA. For the other three species, the largest response ratio was for ULR. Across all species, the average response was a 37% increase in LWR, a 12% increase in ULR and a 4% decrease in SLA at high vs. low nitrogen. Interspecific differences in growth response to nitrogen were associated primarily with interspecific differences in the ULR response ratio. The rank-order correlation between ULR response ratio and RGR response ratio was 0.88. Re-analysis of previous experiments on plant nutrient response showed a similar pattern; in all studies interspecific variation in the response of RGR to nutrients was associated primarily with variation in ULR response ratio. Interspecific differences in the RGR response ratio were not significantly correlated with either SLA response ratio or LWR response ratio in any of the studies. These results strongly suggest that differences in the extent to which plant species respond to nutrients with increased growth are associated primarily with differences in how ULR responds to nutrient supply.

KEY WORDS: growth analysis, net assimilation rate, unit leaf rate, relative growth rate