Shifts in the Microbial Community Involved in the Nitrogen Cycle of Agricultural Soil
Microenvironments. (4980)
Authors:
J.A. Izquierdo* - University of Massachusetts, Amherst K. Nuesslein - University of Massachusetts, Amherst
Abstract:
Microbial communities regulate a significant portion of the nitrogen cycle in soils.
But we still know very little about the microscale distribution of the diverse soil community in these processes. In this study, we aim to examine the effect of tillage and microenvironment separation on the distribution of three nitrogen processes.
Soil has been separated into four sieved fractions: a macroaggregate (2000-600 um in diameter), a large microaggregate (600-250 um), a small microaggregate (250-75 um) and a clay-silt fraction (under 75 um). Soils were obtained from adjacent
agricultural plots under different tillage treatments: an untilled, a newly tilled and a long-term tilled plot. DNA clone libraries were constructed targeting genes
involved in nitrogen fixation (nifH), nitrate reduction (narG) and ammonia
oxidation (amoA). Dramatic changes were observed in the distribution of nifH and narG between the untilled and the newly tilled plots, marked by drops in the
proteobacterial and compensating increases in the proportion of anaerobic
diazotrophs. Cumulative shifts between soils caused by the tillage treatments were also observed, with newly tilled plots resulting in significant increases of
rhizosphere-associated uncultured diazotrophs and in overall narG diversity. We hypothesize that this is caused, respectively, by the release of endophytes and nutrients from the rhizosphere.
Speaker Information: Javier Izquierdo, University of Massachusetts, Amherst, 33 Pine Street, Amherst, MA 01002; Phone: 413-5451204; E-mail: [email protected]
Session Information: Tuesday, November 2, 2004, 9:00 AM-11:00 AM Presentation Start: 9:00 AM (Poster Board Number: 2821)
Keywords: microenvironment; nitrogen; microaggregate; nifH
