Quantitative Analysis of Pedogenic Thresholds and Domains in Volcanic Soils
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Quantitative Analysis of Pedogenic Thresholds and Domains in Volcanic Soils Jesse Bloom Bateman,1,2* Oliver A. Chadwick,3 and Peter M. Vitousek4 Department of Earth System Science, Stanford University, Stanford, California 94305, USA; Institute of the Environment and Sustainability, University of California, Los Angeles La Kretz Hall, Suite 300 Box 951496, Los Angeles, California 90095-1496, USA; Department of Geography, University of California, Santa Barbara, California, USA; Department of Biology, Stanford University, Stanford, California 94305, USA
ABSTRACT Pedogenic thresholds describe where soil properties or processes change in an abrupt/nonlinear fashion in response to small changes in environmental forcing. Contrastingly, soil process domains refer to the space between thresholds where soil properties are either unchanged, or change gradually, across a broad range of environmental forcing. Here, we test quantitatively for the presence of thresholds in patterns of soil properties across a climatic gradient on soils developed from about 20-ky-old basaltic substrate on the Island of Hawai’i. From multiple soil properties, we quantitatively identified a threshold at about 750 mm/y of water balance (precipitation minus potential evapotranspiration), delineating the upper water balance boundary of soil fertility in these soils. From the threshold in the ratio of exchangeable Ca to total Ca, we identified the lower water balance boundary of soil fertility in these soils at −1000 mm/y; however, this threshold
was qualitatively described as it lies near the limit of the climate gradient data where the statistical approach cannot be applied. These two results represent the first time that pedogenic thresholds have been identified using statistically rigorous methods and the limitations of said methods, respectively. Comparing the 20-ky soils to soils that developed on basaltic substrates of 1.2 ky, 7.5 ky, 150 ky, and 4100 ky in a time–climate matrix, we found that our quantitative analysis supports previous qualitatively identified thresholds in the soils developed from older substrates. We also identified the 20 ky as the transition from kinetic to supply limitation for plant nutrients in soil in this system. Key words: Hawai’i; pedogenic thresholds; process domains; water balance; volcanic soil; biological uplift; pedogenesis; breakpoints.
HIGHLIGHTS Received 31 January 2018; accepted 10 February 2019 Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-019-00361-1) contains supplementary material, which is available to authorized users. Author Contributions JBB, OAC, and PMV designed the study. JBB carried out the field sampling and data analysis and wrote the first draft, with guidance from OAC and PMV. All authors participated in revising the analyses and manuscript. *Corresponding author; e-mail: [email protected]
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We explore the climatic controls on soil biogeochemistry with novel statistical methods. We found evidence for two thresholds in the d
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