『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 cncentrations 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 334μmol
L-1 under pine. Silicon and base cation fluxes indicate
higher weathering rates under pine. Soltion chemistry shows that
canopy and nutrient cycling processes are different between the
two species and are impacting the cation loss rates.
Keywords: Chaparral; Soil soltion chemistry; Base cations; Atmospheric
deposition; Mineral weathering』
1. Introduction
2. Methods
3. Field methods
4 Results
4.1. Canopy processes
4.2. The influence of vegetation on soil biogeochemistry
5. Discussion
5.1. Canopy processes
5.2. The influence of vegetation on soil biogeochemistry
5.3. Implications for weathering rates
6. Conclusions
References