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Title: BASE CATION AND SILICON BIOGEOCHEMISTRY UNDER PINE AND SCRUB OAK MONOCULTURES: IMPLICATIONS FOR WEATHERING RATES

Author
item JOHNSON-MAYNARD, J - UNIV OF IDAHO, MOSCOW
item GRAHAM, R - UC RIVERSIDE, CA
item Shouse, Peter
item QUIDEAU, S - UNIV ALBERTA, CANADA

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2004
Publication Date: 11/23/2004
Citation: Johnson-Maynard, J.L., Graham, R.C., Shouse, P.J., Quideau, S.A. 2004. Base cation and silicon biogeochemistry under pine and scrub oak monocultures: implications for weathering rates. Geoderma. 126: 353-365

Interpretive Summary: Understanding the relationship between vegetation type and soil forming processes such as mineral weathering is a difficult task considering the interactions between biotic and abiotic soil forming factors. Using a true biosequence, allowed us an opportunity to link biogeochemical processes to mineral weathering in soils. We measured all relevant inputs and outputs and found that for pine vegetation atmospheric deposition of chemicals is more important than for scrub oak. In scrub oak, canopy leaching was an important input of chemicals to the soil. Nutrient cycling was also faster in oak than pine. Silicon and base cation fluxes indicated that pine vegetation type caused higher weathering rates than scrub oak. Soil solution chemistry shows that canopy and nutrient cycling processes are different between pine and scrub oak and are impacting the cation loss rates at different rates causing different soils to form after only 5 decades.

Technical Abstract: Vegetation type has a profound influence over biogeochemical processes, including canopy leaching, stemflow, litterfall, and nutrient uptake. Understanding the relationship between plants and soil processes such as mineral weathering is a difficult task considering the interactions among biotic and abiotic soil forming factors. In this study, soils planted with pure stands of scrub oak (Quercus dumosa Nutt.) and Coulter pine (Pinus coulteri B. Don) were used to identify key biogeochemical processes in each soil-plant system. The experimental design, a true biosequence, allowed an opportunity to link biogeochemical processes to mineral weathering. Precipitation, throughfall, litter leachate, and soil solutions were collected following rain events from November of 1996 to April of 1998. Relatively high Na and Ca concentrations in pine throughfall suggest that atmospheric deposition is a more important process within the pine canopy than is canopy leaching. In contrast to pine throughfall, mean K concentrations were higher than Ca in oak throughfall, reflecting the importance of canopy leaching. Nutrient cycling was more rapid within the scrub oak soil/plant system as evidenced by significantly reduced levels of cations in soil solution at the 7.5-cm depth compared to litter leachate. Mean Si concentrations at the 65-cm depth were 334 micro-mol L-1 under oak and 431 micro-mol L-1 under pine. Silicon and base cation fluxes indicate higher weathering rates under pine. Solution chemistry shows that canopy and nutrient cycling processes are different between the two species and are impacting the cation loss rates.