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Title:   Author  item
                                            Caesar, Thecanitem
                                            Stevens, William

                                                         - *Bart*item
                                            Sainju, Upendraitem
                                            Caesar, Anthonyitem
                                            Gaskin, Johnitem
                                            West, Mark
  Submitted to: Soil Science
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 3/28/2014
                                    Publication  Date: N/A
                                    Citation: N/AInterpretive Summary: By understanding how soil water content and organic matter influence the predominant heterotrophic populations of culturable soil-aggregating bacteria, we can gain insight into specific communities (species composition) that are important players in the formation and stability of macroaggregates. We explore the changes of soil-aggregating bacterial communities in microagggregates (0.25-0.05 mm in diameter) held inside macroaggregates (> 0.25 mm) caused by irrigation and tillage practices of an agricultural system cropped to barley and a Conservation Reserve Program (CRP) plantation and to relate these changes to the process of soil aggregation. Data indicating a dominance of soil-aggregating Pseudomonads and Stenotrophomonas maltophilia populations in microaggregates held within macroaggregates of soils under irrigated no-till barley and CRP suggesting that these bacteria can proliferate throughout the surface soil matrix wherever microbial activity associated with organic resources occurs and their activity in producing extracellular polymeric substances (polysaccharides) could contribute to macroaggregate formation and stability.
                                Technical Abstract: Little is known about the microbial community structure associated with soil aggregation in microaggregates (0.25-0.05 mm) that are held within macroaggregates (> 0.25 mm). We investigated the effects of irrigation, tillage and cropping system on aggregate distribution and the community structure of the predominant culturable bacteria in microaggregates held within macroaggregates from 2005 to 2008 at a site in western North Dakota, USA. Managements were malt barley (Hordeum vulgare L.) under no-till and conventional-till and an established no-tilled Conservation Reserve Program (CRP) plantation on Lihen loam (sandy, mixed, frigid, Entic Haplustolls) under irrigated and dryland systems. We hypothesized that microaggregates held within macroaggregates of irrigated no-till barley and CRP management have a higher proportion of the predominant culturable bacterial species that have the capability to aggregate soil than in irrigated and non-irrigated conventional-till barley managements. Fatty acid profiling and DNA sequencing were used to identify bacterial isolates and a soil sedimentation assay to determine their soil-aggregating ability. The proportion of soil aggregating Gram-negative bacteria, dominated by Pseudomonads and Stenotrophomonas maltophilia, were higher under irrigated no-till barley and CRP compared with the other managements. Species abundance and diversity of the soil-aggregating bacterial isolates was the highest in irrigated no-till barley and CRP and the lowest in irrigated conventional-till barley. We demonstrated that microaggregates held within macroaggregates represent a unique microenvironment that select for specific soil-binding microbial communities under irrigated management that develop continuous surface plant residue input, which may contribute to high soil structural stability and resilience at 0-5 cm depth.


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