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Nematodes As Bioindicators of Soil Food Web

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Nematodes As Bioindicators of Soil Food Web NEMATODES AS BIOINDICATORS OF SOIL FOOD WEB HEALTH IN AGROECOSYSTEMS: A CRITICAL ANALYSIS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By SHABEG SINGH BRIAR * * * * * The Ohio State University 2007 Dissertation Committee: Professor Parwinder S. Grewal, Adviser Professor Sally A. Miller, Adviser Professor Casey W. Hoy Professor Landon H. Rhodes Approved by Advisers ____________________ ____________________ Plant Pathology Graduate Program Abstract Nematodes occupy a central position in the soil food web occurring at multiple trophic levels and, therefore, have the potential to provide insights into condition of the soil food webs. I hypothesized that differences in management strategies may have differential effects on nematode community structure and soil properties. This hypothesis was tested in three different replicated experiments. In the first study a conventional farming system receiving synthetic inputs was compared with an organically managed system and in the second study four different farming strategies with and without compost application transitioning to organic management were compared for nematode communities and soil characteristics including soil bulk density, organic matter, microbial biomass and mineral-N. The third study was aimed at assessing the indicative value of various nematode measures in five habitats. Nematode food webs were analyzed for trophic group abundance and by calculating MI, and enrichment (EI), structure (SI) and channel indices (CI) based on weighted abundance of c-p (colonizer-persister) guilds. Bacterivore nematodes were more abundant in the organic than the conventional whereas the conventional system had higher population of the root lesion nematode, Pratylenchus crenatus compared with organic system. Organic hay plots had the lowest populations of P. crenatus compared to corn, soybeans and oats. Enrichment ii opportunists c-p 1 and general opportunists c-p 2 bacterivores were higher in composted than the non-composted strategies. Population of Pratylenchus sp. was significantly lower but that of c-p 2 plant parasites Tylenchus and Filenchus were higher in the composted compared with non-composted amended soils. Principal components analysis indicated that MI, SI and EI contributed the most to differences between the habitats. Forests and shrublands had highly structured food webs as expected but their high enrichment may be unique due to the muck soils. Croplands showed a clear distinction from other habitats with less structured food webs. Turfgrass lawns occupied an intermediary position between disturbed and unmanaged habitats. Lack of increase in SI in the organic farming system could be due to the high tillage requirement, which might have suppressed the population of high c-p value tillage- sensitive nematodes. iii DEDICATED TO MY PARENTS iv ACKNOWLEDGMENTS During the course of my thesis work, there were many people who were instrumental in helping me. Without their guidance, help and patience, I would have never been able to accomplish the work of this thesis. First, I wish to thank my advisers, Dr. Parwinder Grewal and Dr. Sally Miller for intellectual support, encouragement, and enthusiasm, which made this thesis possible, and for their patience in correcting both my stylistic and scientific errors. I thank my advisory committee members, Dr. Casey Hoy and Dr. Landon Rhodes for their guidance, help, academic support and constructive suggestions that opened my eyes to much deeper insight in my research project. Also I want to thank all members of Dr. Grewal’s lab for their compassion, friendship and help, especially Dr. Ganpati Jagdale. Also I want to thank all the faculty members and staff of the Department of Plant Pathology for their help, time and the highest level of education. I would like also, to express my deep respect and gratitude for all members of the Department of Entomology, where I conducted my entire research project. I do not want to forget to thank my wife (Ruby), and two sons (Robin and Monty) for their patience during stressful times. v VITA April 3, 1973.............................................Born-Faridkot, India. 1995 -1997………………………………Master of Science, Nematology and Plant Pathology, Punjab Agricultural University, Ludhiana, Punjab, India. 2003-Present…………………………….Graduate Research Associate, The Ohio State University. EMPLOYMENT September 1998-March 2003…………...Assistant Professor of Nematology, Punjab Agricultural University, Punjab, India. September 1997-August 1998………...Research Associate, Department of Plant Pathology, Punjab Agricultural University, Ludhiana, Punjab, India. FIELD OF STUDY Major: Plant Pathology vi TABLE OF CONTENTS Page Abstract .................................................................................................................……..ii Dedication .............................................................................................................……..iv Acknowledgments...................................................................................................….....v Vita.........................................................................................................................…......vi List of Tables...........................................................................................................…....ix List of Figures.....................................................................................................……....xii Chapters: 1. Introduction...............................................................................………………………....1 2. Soil nematode community, organic matter, microbial biomass and nitro gen dynamics in field plots transitioning from conventional to organic management……….....................................................................................…….….......11 2.1 Introduction……………………………………………………………….……......11 2.2 Materials and methods….…………………………………….…………………....14 2.3 Results…………………………………………………………………..……….....18 2.4 Discussion……………………………………………………………………….....20 2.5 Summary…………………………………………………...…………………........24 2.6 References…………………………………………………………………….........26 3. Effect of compost or non-compost based organic transitioning strategies on soil nematode community, organic matter, microbial biomass and nitrogen dynamics…...44 3.1 Introduction……………………………………………………………………......44 vii 3.2 Materials and methods……………………………………….………………….....47 3.3 Results………………………………………………………………………..……51 3.4 Discussion………………………………………………….……………...………55 3.5 Summary……………………………………………...…………………………...59 3.6 References………………………………...…………………………………….…61 4. An assessment of the indicative value of nematode trophic group abundance and food web indices in differentiating habitats with a gradient of anthropogenic impact…...................................................................................................................….79 4.1 Introduction………..……………………………………………………………...79 4.2 Materials and methods…..………………………………………………………..82 4.3 Results……………………………………………………………………………85 4.4 Discussion..………….……………………………….…………………………...88 4.5 Summary………………………………………………………………………….93 4.6 References………………………………………………………………………...94 5. Synthesis and future directions……………………………………………….……..109 Bibliography………………………………………………………………………..122 viii LIST OF TABLES Table Page 2.1 List of nematode genera identified at the experimental site in conventional and organic farming system plots …………………………………………………….35 2.2 Effect of farming systems on nematode trophic groups, root lesion nematode Pratylenchus crenatus and nematode community indices including enrichment (EI), structure (SI), and channel index (CI) from spring 2000 to spring 2004…………….....…………………………………………..………..36 2.3 Effect of farming systems on soil bulk density (BD), total organic matter % (TOM), particulate organic matter (0.05-2 mm) (POM), % mineral + associated organic matter (MAOM) (<0.05 mm), mineral-N (NH4 -N - -1 and NO3 -N (µg g dry soil), and microbial biomass-N (MB-N).……….……....37 2.4 Mean soil bulk density (BD), total organic matter % (TOM), particulate organic matter (0.05-2 mm) (POM), % mineral associated organic matter + - -1 (MAOM) (<0.05 mm), mineral-N (NH4 -N and NO3 -N (µg g dry soil), and microbial biomass-N (MB-N) in conventional and organic arming systems…………………………...........................................................................38 3.1 Description cropping sequences of four main plot management strategies: fallow, mixed species hay, low intensity vegetables as open field vegetables and intensive vegetable production under high tunnels...…….………69 ix 3.2 Effect of main plot strategies and compost on nematode c-p groups and food web indices [enrichment (ei), structure (si), and channel index (ci)]..…….….….................................................................................…........70 3.3 Comparison between main plot strategies with and without compost on nematode c-p guilds (Bf: bacterivore; Ff: fungivores; Om: omnivores; Pr: predatory and Pp: plant-parasites) from 2003 and 2006 soil sampling..…………………......................................................…………………....71 3.4 Effect of main plot strategies and compost on soil properties [bulk density (BD), organic matter % (TOM), % mineral associated organic matter (MAOM) (<0.05 mm), particulate organic matter (0.05-2 mm) (POM), mineral-N + - -1 (NH4 -N and NO3 -N (µg g dry soil), and microbial biomass-N (MB-N) (µg g-1)]……………......................................................................................……..73
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