Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2010
Publication Date: 5/1/2010
Citation: Acosta Martinez, V., Dowd, S.E., Sun, Y., Allen, V.G., Wester, D. 2010. Pyrosequencing analysis for characterization of bacterial diversity in a soil as affected by integrated livestock-cotton production systems. Applied Soil Ecology. 45(1):13-25. Interpretive Summary: In the Southern High Plains region of Texas, an effort between USDA and Texas Tech University was initiated since 1997 to evaluate the economics, water savings from Ogallala Aquifer and soil quality between the typical continuous cotton system and an integrated cropping-livestock system that included cotton, forage, and Angus-cross stocker beef steers. For the integrated system, steers grazed in sequence a perennial warm-season grass paddock, and then rye and wheat grown in two paddocks (stages) of a rotation with cotton. As a part of the evaluation of soil quality and functioning, the bacterial diversity of soil was evaluated after 10 years under these systems. Bacterial populations are important in soil processes that decompose pollutants, provide nutrients to the system, and fix atmospheric nitrogen. Bacteria also combat pathogens and act as buffers that maintain the balance of ecosystems. This study found positive correlations between certain bacteria (Protobacteria, Firmicutes, Chloroflexi, Verrucomicrobiae and Fibrobacteres) and the activities of enzymes involved in C and P cycling, which were increased in soil under the integrated livestock-cotton system. In addition, trends on the predominant bacteria under the integrated livestock-cotton system (i.e., Protobacteria) may indicate the bacteria playing a major role in soil processes that were increased under the integrated livestock-cotton system.
Technical Abstract: Impacts of integrated livestock-crop production systems compared to specialized systems on soil bacterial diversity have not been well documented. We used a bacterial tag encoded FLX amplicon pyrosequencing (bTEFAP) method to evaluate bacterial diversity of a clay loam soil (Fine, mixed, thermic Torrertic Paleustolls) after 10 yrs under an integrated livestock (beef)-cotton system compared to continuous cotton (Gossypium hirsutum L.) in a semiarid region. In the integrated system, cattle alternatively grazed a perennial warm-season grass [Bothriochloa bladhii (Retz) S.T. Blake] paddock and small grains grown in a two-paddock wheat (Triticum aestivum L.)- fallow-rye (Secale cereal L.)-cotton rotation. Maximum observed number of unique sequences operational taxonomic units (OTU) at 3% dissimilarity level (roughly corresponding to the species level) corresponded to 1,200 and 1,100 at 0-5 cm and 5-15 cm depths, respectively. Predominant phyla at 0-5 and 5-15 cm in this soil (up to 65% of abundance) despite system effects were Protobacteria, Actinobacteria, and Gemmatimonadetes. Protobacteria were more predominant in soil under the integrated livestock-cotton system compared to Ct-Ct whereas Bacteroidetes were more predominant under Ct-Ct. Chlorofexi, Verrucomicrobiae, Acidobacteria and Spirochaetes were more abundant under fallow periods of the rotation compared to systems sampled under cotton (Rye-Cotton-Wheat-Fallow or Ct-Ct) or grass (i.e., pasture). Grazing effects were significant for Actinobacteria, '''and'''Protobacteria, Bacteroidetes, Caldilineae, Thermomicrobia, Spartobacteria, and Nitrospira. Only Nitrospira, Planctomycetacia, and Chlorofexi showed decreases with soil depth. Positive correlations between certain bacteria (Protobacteria, Firmicutes, Chloroflexi, Verrucomicrobiae and Fibrobacteres) and the activities of alkaline phosphatase and '-glucosidase were found.