Theses and Dissertations

Date of Award


Document Type


Degree Name

Master of Science (MS)


Agricultural, Environmental, and Sustainability Sciences

First Advisor

Dr. Engil Isadora Pujol Pereira

Second Advisor

Dr. Teresa Patricia Feria

Third Advisor

Dr. Mirayda Torres-Avila


Fungicide applications are effective to prevent fungal pathogens that are known to cause crop damage and decrease yields. However, these pesticides can exert toxic or inhibitory effects on non-targeted organisms such as soil microbial communities. In addition, it is unknown to what extent shifts in temperature and soil moisture resulting from global climate change, alter the activities of non-targeted soil organisms. The aim of this study was to evaluate soil biological parameters such as soil respiration and enzyme activities involved in the cycling of carbon, nitrogen, and phosphorous (Beta-glucosidase, Fluorescein Diacetate (FDA) Hydrolysis, urease, alkaline phosphatase, acid phosphatase, and N-acetyl-Beta-glucosaminidase) from the use of fungicides, azoxystrobin and tebuconazole, with anticipated temperatures and moisture levels based on the Intergovernmental Panel on Climate Change (IPCC) Representative Concentrated Pathway 8.5 scenario (RCP 8.5) from the end of the century (2070-2100) in the Lower Rio Grande Valley, Texas, U.S.A. A total of 30 random samples were collected from a loamy sand soil in Raymondville, Texas (26° 28’ 57.69” N and 97° 55’ 53.21” W) for a 45-day incubation period under a microcosm approach. The microbial communities’ responses to fungicide, increasing temperatures, and decreasing moisture alone and in combination were studied in a factorial experiment, resulting in a total of 12 treatments with 12 replicates each, comprised of three fungicide treatments (azoxystrobin, tebuconazole, and no fungicide control) applied accordingly by the recommended manufacture rate, two temperature levels (24ºC and 28ºC), and two soil moisture levels (8% and 9%). Results indicated FDA was increased by tebuconazole at 28ºC, however other indicators were suppressed or unchanged. This may indicate other processes were enhanced that were not measured in this study. With increments of temperatures, Beta-glucosidase, and phosphatase activities reduced rates. Tebuconazole significantly decreased Beta-glucosidase and phosphatase activities, while azoxystrobin significantly lowered urease rates. Decreased microbial activities due to temperature, moisture, and fungicide, may therefore impact nutrient availability to other microbes and plants. Solely moisture reduction had no significant impact on soil microbial activities. Therefore, it is imperative to protect soil ecosystems to aid the sustainability of agriculture and support healthy ecosystems. Future research should consider whether microbial functioning can withstand the long-term exposure to these disturbances, exploring adaptation mechanisms (e.g., shifts in microbial diversity) upon ecosystem-based strategies for prevention of crop diseases.


Copyright 2022 Armida Rivera. All Rights Reserved.