Date of Award

Spring 5-1-2018

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences

Committee Chair

Micheal Davis

Committee Chair Department

Biological Sciences

Committee Member 2

Jake Schaefer

Committee Member 2 Department

Biological Sciences

Committee Member 3

Mac Alford

Committee Member 3 Department

Biological Sciences

Committee Member 4

Carl Qualls

Committee Member 4 Department

Biological Sciences

Committee Member 5

Kevin Kuehn

Committee Member 5 Department

Biological Sciences


Due to the continuing increases is atmospheric carbon dioxide levels and its potential effect on food sources, there is an interest in evaluating the effect of elevated CO2 concentration versus ambient CO2 concentration in agricultural crop plants although more studies have focused on the aboveground portions of plants rather than the roots. Additionally, the conservation agricultural method, no-till, has been widely suggested as a possible method of increasing soil organic carbon and increasing soil moisture in a hotter world.

This research involves two major agricultural plants, Sorghum bicolor (sorghum), and Glycine max (soybean) grown under four conditions including conventional till elevated, conventional till ambient, no-till elevated, and no-till ambient. These plants, along with three rotating cover crops, were grown in open top chambers (OTCs) at the USDA-ARS National Soil Dynamics Laboratory at Auburn, Alabama as part of a series of related studies. The cover crops were not used during conventional tillage and were grown under no-till elevated and no-till ambient conditions.

The first part of the study involved comparing root growth response to the treatments of the important agricultural plants, sorghum and soybean. There was a trend toward greater standing root crop with sorghum using no-till cropping methods. There was a significantly greater average root length of sorghum in deeper soil and a trend toward elevated atmospheric CO2 concentration being associated with increased average root length of sorghum. For soybean, there was a significant effect of no-till on average root diameter.

The second area of focus involved comparing the three legumes in the study at no-till elevated CO2 concentration at 720 µmol mol- and no-till ambient CO2 concentrations at 365 µmol mol-1conditions. This included soybean (Glycine max (L.) Merrill), sunn hemp (Crotalaria juncea L), and scarlet clover (Trifolium incarnatum L.). There was a species difference, as postulated previously, with sunn hemp having a significant growth response to elevated CO2 concentration while there was less increased root growth from the other two legumes. Additionally, both sunn hemp and soybean had increased root growth in deeper soil (17 – 34 cm) which clover did not.

The third portion of the study involved a comparison of a C3 cover crop grass, wheat (Triticum aestivum L.), with a C4 grass (Sorghum bicolor L.), at no-till ambient and no-till elevated conditions. In this case, both members of family Poaceae had root growth response to elevated CO2 concentration, which although not identical, did not support earlier indications of C3 plants having an advantage in elevated CO2 concentration.