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Determining Vertical Root and Microbial Biomass Distributions from Soil Samples
Author(s) -
Cook Freeman J.,
Kelliher Francis M.
Publication year - 2006
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2005.0173
Subject(s) - mathematics , sampling (signal processing) , biomass (ecology) , power function , probability density function , statistics , exponential function , interval (graph theory) , function (biology) , soil science , mathematical analysis , environmental science , ecology , physics , combinatorics , biology , evolutionary biology , detector , optics
When vertical density distributions of root or microbial biomass are calculated using each sampling interval's midpoint as the depth coordinate, the calculated distribution is biased if it is a nonlinear function with depth. In the root biomass literature, distributions are often described by a power function R ∝ β z , where β is a decay coefficient and z is depth. A common alternative formulation is an exponential function, R ∝e − z / Z r, where Z r is a characteristic length scale. These functions are equivalent when Z r = −1/ln β, so the data according to either function may be unified. The bias can be eliminated by representing the vertical distribution with a continuous function, integrating it over the sampling interval, and using a least squares method to determine the function's parameters. The bias increased by nearly threefold when the sampling interval increased from 0.01 to 1 m. As the sampling interval increases, the bias shifts the function down the z axis. This results in the intercept increasing with increasing sampling interval. When a single profile was sampled at different intervals, the function's intercept and Z r changed. The parameter Z r changed fivefold when the sampling interval increased from 0.1 to 0.5 m, while the calculated fraction of roots above a depth of 0.1 m decreased threefold for the same change in sampling interval. Beneath a tropical forest where root biomass and microbial respiration were sampled throughout the same soil profile, the corresponding microbial and root biomass length scales averaged 0.17 m and differed by only 11%.