Degree

Master of Science (MS)

Department

Plant Pathology and Crop Physiology

Document Type

Dissertation/Thesis

Abstract

In Louisiana, sugarcane has been grown in the same soils for over 200 years. A phenomenon wherein soils with a long-term sugarcane cropping history produce decreased yields compared to adjacent land without a recent history of sugarcane cultivation has been documented in multiple sugarcane growing regions. Research in both Louisiana and internationally has shown positive plant growth responses when soils with a long-term cultivation history are sterilized or treated with selective biocides, suggesting there is a biological component to the underlying soil health issue. In this study, soil microbial ecology was compared for paired sites with short and long-term sugarcane cropping histories at six locations in plant cane and two in plant cane and first ratoon. Yield estimates of paired sites revealed crops grown in short-term cultivation soils generally out-yielded their long-term counterparts. Soil properties that can influence microbial ecology, including soil organic matter, macro and micronutrients, and soil extracellular enzymes, were generally present at higher levels in short-term cultivation soils, but varied by location. Root staining revealed greater fungal endophyte colonization in long-term cultivation soils. Distance-based redundancy analysis of fatty acid methyl ester biomarkers revealed differences in community structure based primarily on location but also cropping history. Analysis of 16S prokaryotic and ITS fungal amplicon-based metagenomic β-diversity data revealed prokaryotic community structure was also primarily influenced by location, whereas fungal communities differed based on cropping history. This suggests fungi are major contributors to the detrimental effects associated with sugarcane monoculture. Additional α-diversity comparisons of 16S and ITS metagenomes revealed portions of prokaryotic and fungal communities were more commonly associated with short and long-term sugarcane cultivation in both bulk and rhizosphere soils. Candidate microorganisms beneficial to sugarcane growth that were more abundant in soils with a short-term cropping history included 107 prokaryotic genera and 37 fungal genera in bulk soils and 97 prokaryotic genera and 46 fungal genera in rhizosphere soils. Candidate microorganisms detrimental to sugarcane growth that were more abundant in soils with a long-term cropping history included 117 prokaryotic genera and 58 fungal genera in bulk soils and 94 prokaryotic genera and 40 fungal genera in rhizosphere soils.

Date

8-18-2017

Committee Chair

Hoy, Jeffrey

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