1. Jessica Williamson
St. Edward’s University School of Natural Sciences
Austin, TX
Concentration Effects of Plant Growth Promoting Rhizobacteria on
Nolina lindheimeriana in Differing Organic Matter
The overuse of fertilizers to promote plant growth has caused global human health and
environmental issues. However, recent research indicates that the need for fertilizer could be
reduced or eliminated through an increased awareness of beneficial soil microorganisms that
promote plant growth. These plant growth promoting rhizobacteria (PGPR), such as bacteria of
the Pseudomonas genus, benefit plants by promoting root hair growth to increase root
absorption, increasing nutrient availability, and producing phytohormones to also increase plant
growth. Thus, the goal of this research was to observe the effects of PGPR concentration on the
native Texas plant, Nolina lindheimeriana, planted in soil with different levels of organic matter.
I expected to detect a positive relationship between plant growth and PGPR concentration, with
the greatest effects of PGPR on plant growth occurring in plants grown in low organic matter
soil. To begin, I isolated PGPR in the Pseudomonas genus from root samples cultured in
Pseudomonas broth. I confirmed the identity of the isolates using gram staining, microscopy, and
molecular analyses. Using colony forming units and optical density measurements (at 600nm), I
was able to quantify the amount of Pseudomonas bacteria present in the plant rhizosphere as a
baseline concentration. Nine Nolina lindheimeriana were watered every two days with 100mL of
water and 100mL of Pseudomonas broth as a baseline: three planted in high organic matter, three
in low organic matter, and three in normal organic matter. Another nine plants in the same three
organic matter conditions were watered every two days with 100mL of water, 100mL of
Pseudomonas broth and three times the original amount of Pseudomonas bacteria present in the
plant rhizosphere. Compared to the controls, adding a high concentration of PGPR to the plants
resulted in an increase in plant growth and root growth. However, the stimulation by PGPR was
greater in high organic matter than in low organic matter. Overall, a higher concentration of
PGPR, namely bacteria of the Pseudomonas genus, had a positive influence on the growth of
Nolina lindheimeriana, particularly in high organic matter compared to low organic matter soil.
Future experiments may focus on other genera, such as the Azospirillum and may increase the
range of concentrations tested in order to effectively compare the PGPR additions to the effects
of chemical fertilizers