Date of Award

5-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Dr Taouflk KSlksl

Second Advisor

Dr Khaled Tarablly

Third Advisor

Dr Shyam Kurup

Abstract

Atmospheric carbon dioxide (CO2) concentrations have been increasing for many decades. The impact of such greenhouse gas has been reported to affect ecosystems at all levels. Elevated atmospheric CO2 can affect the growth of plants and their response to water intake. But, different plants show different degrees of response depending on whether they have C3 or C4 photosynthetic pathway. The aim of this study is to evaluate the effect of CO2 enrichment on the growth and microbial activity of alfalfa (Medicago sativa) and Rhodes grass (Chloris gayana) and also its effect on the water use efficiency (WUE) of these plants. Both plant species were exposed to ambient CO2 (ACO2; ~500 ppm), enriched CO2 (ECO2; ~ 1000 ppm) under regular watering regime or under water stress. Soil samples were tested for microbial activity using Fluorescein diacetate (FDA) hydrolysis technique, shoot and root lengths were measured periodically, WUE was calculated using fresh and dry weight of the plants, and numbers of leaves were counted. Microbial activity under elevated CO2 was 41 % higher in Rhodes grass at water stress, than in ambient CO2 Also, by inducing water stress on Rhodes grass, the WUE increased significantly by 4.6 times i.e. 21.5% than its control counter parts. Moreover, WUE of alfalfa in the treatment (elevated CO2 + water stressed) group was 25.7% (3.8 times) greater than alfalfa grown at control (ambient CO2 + normal water). Fresh weight biomass of Rhodes grass under treatment group showed no significant difference compared to the control group, whereas the biomass of alfalfa was significantly higher in both fresh (4%) and dry matter (11 .3%) under treatment group, compared to the control group. Height of alfalfa grown under CO2 enrichment was 30% lesser at water stress, than compared to the ones grown at normal water conditions. Shoot/root ratio of Rhodes grass grown under elevated CO2 was 28.8% lower than the ones grown at ambient CO2 concentrations, whereas shoot/root ratio of alfalfa grown under CO2 enrichment was 22.9% higher than the ones grown at ambient CO2 concentrations. Number of leaves remained the same for both Rhodes grass and alfalfa under every treatment.

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