RHIZOSPHERE INTERACTIONS AS DETERMINANTS OF MICROBIAL COMMUNITY ASSEMBLY IN A TROPICAL SOIL

Item Summary

Title:	RHIZOSPHERE INTERACTIONS AS DETERMINANTS OF MICROBIAL COMMUNITY ASSEMBLY IN A TROPICAL SOIL
Authors:	DHUNGANA, ISHWORA
Contributors:	Nguyen, Nhu N. (advisor) Tropical Plant and Soil Sciences (department)
Keywords:	Soil sciences Microbial communities Oxisol Plant species Planting cycle show 2 moreRoot exudates Soil microbes show less
Date Issued:	2020
Publisher:	University of Hawai'i at Manoa
Abstract:	Terrestrial plants and their root systems interact strongly with soil and soil microbes, especially in the rhizosphere. This strong interaction is because of the chemical compounds released by plant roots known as “root exudate”. However, there exist limited evidence to support the idea that different plant species have the ability to drive soil microbial community structure, especially across time in a field setting. In addition, there exists a huge gap that studies the mechanism (root exudate) different plant species use to influence rhizosphere microbial communities. I conducted a field experiment to assess how three plant species (Lactuca sativa, Brassica juncea, and Zea mays) under continuous monocropping system-mediated soil microbial (bacterial and archaeal and fungal) community composition in a tropical Oxisol. Furthermore, I performed a lab experiment to look at how root exudates may select for different soil microbes and how rhizosphere microbes respond to the root exudates of different plant species mentioned above. From my field experiment, I show that microbial richness and diversity increases and community composition changes in cultivated soil compared to fallow soil. I found that plant species do not strongly influence bacterial and archaeal richness, diversity, and composition but influences fungal community diversity and composition. I record a strong influence of repeated planting cycles on bacterial, archaeal, and fungal community richness, diversity, and composition. My results demonstrate that plant species has different effect on bacteria and archaea than they do on fungi, but the presence of plants and the length of cultivation has stronger effects on soil microbes than they do plant species. From my lab experiment, I found a suite of both potentially beneficial and phytopathogenic bacteria in the rhizosphere of Lactuca sativa, Brassica juncea, and Zea mays species. When grown with different root exudates, Lactuca sativa rhizosphere bacteria performed better in non-host exudate, Brassica juncea rhizosphere bacteria performed equally well in both host and non-host exudates, whereas Zea mays rhizosphere bacteria performed similarly in host and all non-host exudates. My results demonstrate that as a whole, root exudate profiles from individual plants do not necessarily select for specific microbes, and that apparent selection in the rhizosphere might be associated with other factors specific to the exudates of individual plant species. These findings broaden the understanding of the role that root exudates, an important mechanism, in selecting distinct microbial communities in the rhizosphere. Further research are required to investigate the other factors that drive soil microbial communities.
Pages/Duration:	61 pages
URI:	http://hdl.handle.net/10125/73389
Rights:	All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections:	M.S. - Tropical Plant and Soil Sciences

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