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Root Influence on Nitrogen Mineralization and Nitrification in Avena barbata Rhizosphere Soil

Dep. of Environmental Science Policy and Management, Univ. of California, Berkeley, CA 94720; E. Schwartz, current address: Northern Arizona State Univ., Flagstaff, AZ

View larger version (48K): [in a new window]   Fig. 1. Diagram of plant growth microcosms. About 8 wk after Avena barbata germination, the solid divider separating the two compartments of the microcosm was replaced by a divider with a 5-mm high horizontal slot approximately 3 cm below the soil line. The pattern of root and soil harvest is shown on the right.

View larger version (18K): [in a new window]   Fig. 2. Live, dead, and total bacterial numbers in rhizosphere and bulk soils. Total cells = live cells + dead cells. Cell numbers were log10 transformed before analysis. Error bars indicate standard error of the means.

View larger version (10K): [in a new window]   Fig. 3. Principal component analysis plot of terminal restriction fragment length polymorphism (TRFLP) patterns generated from rhizosphere soil, bulk soil, and control soil. Error bars represent two standards of deviation. Principal component 1 explained 44% of the variation in the data set while component 2 represented 20% of the variation.

View larger version (16K): [in a new window]   Fig. 4. Terminal restriction fragment length polymorphism (TRFLP) fragments present in significantly (p < 0.05) different amounts between rhizosphere and bulk soils. Error bars represent two standards of deviation.

View larger version (13K): [in a new window]   Fig. 5. Rates of potential nitrification, gross nitrification, and NH4 consumption in rhizosphere soil along Avena barbata roots. Error bars indicate standard error of the means. Means sharing a common letter within the same graph are not significantly different (P < 0.05).