Monday, November 5, 2007
96-10
Soil Biotic Interactions and C&N Dynamics with Andropogon gerardii.
Ping Hu1, Charles W. Rice2, Paul White3, Gail Wilson1, and Tim Todd1. (1) Kansas State University - Agronomy, Kansas State University, 2004 Throckmorton Plant Sciences Center, Manhattan, KS 66502, (2) 2701 Throckmorton Hall, Kansas State University, Kansas State University, Department of Agronomy, Manhattan, KS 66506-5501, (3) Kansas State University - Plant Pathology, 2004 Throckmorton, Plant Sciences Center, Manhattan, KS 66506
Although mycorrhizal symbioses (mutualistic associations of plant roots and fungi) are ubiquitous in nature, neither the influences of mycorrhizae on carbon and nitrogen retention nor their effects on soil food webs and nutrient cycling are well understood. This project seeks to determine: 1) the role of mycorrhizal symbiosis on C and N sequestration; 2) the impact of belowground grazers on C and N cycling within the biotic communities; and 3) the interactive feedbacks of sequestered C and nutrient availability on soil biota. Greenhouse and field studies include experimental manipulations of mycorrhizal fungi, nematodes, as a representative of belowgrazers, and soil P availability. Big bluestem (Andropogon geradii), a mycorrhizal dependent plant, was the host plant. Measurements include plant components (roots, rhizomes, shoots), and soil components (microbial biomass, aggregates, total soil mass) for C and N. 15N was used to trace N into different components of the plant-soil system. Mycorrhizae and P significantly increased belowground plant biomass by 41 % and 25%, respectively. Nematodes decreased both above- and below- ground plant biomass in the absence of mycorrhizae and P by 79% and 63%. Mycorrhizae increased rhizome biomass by 72%, while P increased root biomass by 67%. Microbial biomass was not responsive to experimental treatments. Mycorrhizal fungal abundance as indicated by NLFA (Neutral Lipid Fatty Acid) increased the quantity of macroaggregates (>2000), r=0.63. Suppression of mycorrhizae and/or addition of P under field conditions did not significantly affect plant biomass.