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Title: Labile carbon and nitrogen from rhizoplane and surface soils of two perennial grasslands

Author
item GRANT, DOUG - USDA-APHIS
item Reeder, S
item REDENTE, ED - COLORADO STATE UNIVERSITY

Submitted to: Ecological Society of America Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 4/12/2006
Publication Date: 8/7/2006
Citation: Grant, D.W., Reeder, S.J., Redente, E. 2006. Labile carbon and nitrogen from rhizoplane and surface soils of two perennial grasslands. Ecological Society of America Abstracts. GRA-1141-189385 CD-ROM.

Interpretive Summary:

Technical Abstract: In semiarid perennial grasslands biogeochemical processes that drive nutrient dynamics may be more closely related to the quantity of labile SOM than to total SOM. A small ephemeral pool of labile soluble organic matter becomes active after pulse precipitation events. Rhizoplane soil associated with fibrous root systems contains an important fraction of total soluble C. This study examined the relative contribution of rhizoplane soil to the total soluble C present in surface soils (0-10 cm) of northern mixed-grass prairie (NM)) and shortgrass steppe (SGS) ecosystems. Water extractable organic carbon (WEOC) analyses were preformed along with 21-day aerobic incubations for potentially mineralizable carbon (C) and nitrogen (N) to examine relationships between these parameters and root biomass, total soil organic C (SOC), total N (TN) and inorganic N (iN). Roots removed from field moist soil were immediately analyzed for concentration of WEOC and compared with WEOC measurements from bulk soil. Rhizoplane soil associated with coarse roots accounted for 14% and 8% of the total soluble C present in NMP and SGS surface soils, respectively. Concentrations of WEOC in rhizoplane soil were up to 119 times higher than in bulk soil. NMP had greater microbial activity, root biomass and total SOC than SGS, but lower mass of WEOC and iN. Higher microbial immobilization of N (respired CO2/net N mineralized) and lower levels of labile N in the NMP indicate a more C-rich and N-limited microbial environment than in the SGS, leading to lower levels of plant-available N in the NMP.