May 10th, 2013

Abstract for Undergraduate Summer Research Project
Dept. Biology, Student: Esha Ray, Project Directed by Dr. Mozdzer

In light of previous research that has shown that elevated CO2 affects Nitrate assimilation in wheat and Arabidopsis (C3 plants) as well as Ammonium uptake in C4 plants, we propose to conduct an experiment which combines and compares the effects of elevated CO2 on Nitrogen uptake between a C3 sedge (Scirpus olneyi) and a C4 grass (Spartina patens) as well as between native and invasive varieties of the marsh grass Phragmites (Phragmites phragmites and Phragmites australis, respectively). Given the observed negative effect of elevated CO2 on Nitrogen assimilation into plant tissue in general, previous results have predicted that food quality would decline, as well as that C3 plants might dominate over C4 in NH4+ rich systems, but that C4 might out compete C3 in NO3 rich systems under rising concentrations of CO2 within the next half century. It has been conjectured that the reason elevated CO2 has a negative effect on N assimilation in C3 plants at least, is that lowered O2:CO2 ratios in mesophyll reduce photorespiration, of which malic acid and NADP are vital products for the reduction of taken up NO3 to NO2, a process which is necessary for Nitrogen assimilation itself. In addition, it has been found that the invasive marsh grass Phragmites Australis outcompetes the native variety Phragmites Phragmites under conditions of nitrogen enrichment, possibly impairing the capacity of salt marsh soils to act as carbon sinks, as the invasive variety possesses a shallower, less extensive root system, and accumulates belowground biomass and carbon rich dead organic matter at a slower rate than the native Phragmites variety. Specifically, our experiment aims to investigate the effects of elevated CO2 on Nitrogen uptake, the step before assimilation, in C3, C4 and the native and invasive forms of salt marsh grass. The study will involve 5 replicates of the four species each, grown in 6 open top chambers to which 3 different CO3 concs., (320, 420, & 620 ppm) will be delivered, as well as two different levels of N enrichment, crossed in factorial design. Each of the 6 chambers will contain 5 replicates of the 4 plant types, involving 30 plants of each species at a time. After growth under CO2 treatment from 7-12 days, roots will be excised, immersed for 45 minutes in NH4+ compound solution and Urea baths, containing a given concentration of isotopic tracer N15, after which roots will be dried, powdered, and sent for isotopic analysis, to determine the effects of various CO2 treatments on the concentration of N absorbed per unit root mass when exposed in the bath.

Because leaf stomatae of C3 plants tend to close at higher concentrations of CO2, reducing transpiration rates and thus the upward vascular capillary action of water which to a large extent drives nutrient uptake, we predict that elevated CO2 levels may interfere or inhibit Nitrogen uptake in C3 plants at least. Also, depending upon how elevated CO2 stimulates belowground biomass allocation or root production in the two marsh grass varieties, we may observe its varying effects on Nitrogen uptake between them.