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Title: RHIZOSPHERE SOLUTION CHEMISTRY AND THE NUTRIENT STATUS OF JUVENILE CORN, COTTONWOOD, AND SWITCHGRASS PLANTS

Author
item WANG, ZHENYU - IOWA STATE UNIVERSITY
item KELLY, J - IOWA STATE UNIVERSITY
item Kovar, John

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2004
Publication Date: 3/1/2005
Citation: Wang, Z., Kelly, J.M., Kovar, J.L. 2005. Rhizosphere solution chemistry and the nutrient status of juvenile corn, cottonwood, and switchgrass plants. Plant and Soil Journal. 270:213-221.

Interpretive Summary: Recently, soil conservation and water quality advocates have been promoting the use of plant and tree buffers to filter nutrients and sediment from runoff water and near-surface groundwater, so that streams and lakes are not polluted. At this point, we do not fully understand the role of plant uptake in controlling nutrient losses, because our understanding of the dynamics of nutrients in soil solution around roots is limited. In this study, we used a micro-sampling technique to measure spatial and temporal changes in soil solution phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) in the rhizosphere of young corn cottonwood and switchgrass plants. At the end of ten days of measurements, we found that corn plants produced the most roots, and depleted more P and K from solution, than did the cottonwood and switchgrass plants. Nutrient accumulation per unit length of cottonwood root was 37% higher for P, five to 20 times higher for Ca, and one to five times higher for Mg than measured for corn and switchgrass. However, K accumulation per unit length of corn root was two to five times higher than that of the cottonwood and switchgrass. This suggests that the plant species used in a buffer will affect its ability to remove soluble nutrients. These results should be of great interest to commercial growers and conservationists, as well as the fertilizer industry.

Technical Abstract: The ability to sample rhizosphere solution in situ is an important step in improving our understanding of soil solution nutrient dynamics. However, our knowledge of the spatial heterogeneity and temporal dynamics of rhizosphere solution is limited, and even less is known about how rhizosphere solution chemistry varies among plant species. A mini-rhizotron experiment was conducted with juvenile corn (Zea mays L. cv. Stine 2250), cottonwood (Populus deltoides L.), and switchgrass (Panicum virgatum L.) plants grown for 10-d in a fine silty, mixed, mesic Cumulic Hapludoll (Kennebec series). Micro-samples (100-200 ul) of rhizosphere and bulk soil solution were collected at 24-h intervals at a tension of -100 kPa and analyzed for P, K, Ca, and Mg concentration with Capillary Electrophorisis techniques. Plants were harvested at the end of the 10-d period, and tissue digests analyzed for nutrient content by ICP. Corn plants produced roots that were 22% longer than cottonwood, and 87% longer than switchgrass. Similar trends were observed in number of root tips and root surface area. At the end of 10 days, rhizosphere solution P and K concentrations in the immediate vicinity of the roots decreased by approximating 24 and 8%, respectively, for corn, and 15 and 6% for cottonwood. A rhizosphere effect was not found for switchgrass. Corn shoot P, K, and Mg concentrations were 57 to 79% higher than those of switchgrass and cottonwood. Cottonwood shoot Ca concentration, however, was 41 to 57% higher than that of corn or switchgrass. There was no difference in root P concentration among the three species. Nutrient accumulation efficiency of the cottonwood was 37% higher for P, five to 20 times higher for Ca, and one to five times higher for Mg than those of corn and switchgrass. However, K accumulation efficiency of corn was two to five times higher than that of the cottonwood and switchgrass. Nutrient utilization efficiency of P, K, and Mg was higher in cottonwood than in corn and switchgrass. These results suggest that differences in rhizosphere solution chemistry are element-specific and depend on root production and morphology among plant species.