Surficial gains and subsoil losses of soil carbon and nitrogen during secondary forest development.
Abstract
Reforestation of formerly cultivated land is widely understood to accumulate above-
and belowground detrital organic matter pools, including soil organic matter. However,
during 40 years of study of reforestation in the subtropical southeastern USA, repeated
observations of above- and belowground carbon documented that significant gains in
soil organic matter (SOM) in surface soils (0-7.5 cm) were offset by significant SOM
losses in subsoils (35-60 cm). Here, we extended the observation period in this long-term
experiment by an additional decade, and used soil fractionation and stable isotopes
and radioisotopes to explore changes in soil organic carbon and soil nitrogen that
accompanied nearly 50 years of loblolly pine secondary forest development. We observed
that accumulations of mineral soil C and N from 0 to 7.5 cm were almost entirely due
to accumulations of light-fraction SOM. Meanwhile, losses of soil C and N from mineral
soils at 35 to 60 cm were from SOM associated with silt and clay-sized particles.
Isotopic signatures showed relatively large accumulations of forest-derived carbon
in surface soils, and little to no accumulation of forest-derived carbon in subsoils.
We argue that the land use change from old field to secondary forest drove biogeochemical
and hydrological changes throughout the soil profile that enhanced microbial activity
and SOM decomposition in subsoils. However, when the pine stands aged and began to
transition to mixed pines and hardwoods, demands on soil organic matter for nutrients
to support aboveground growth eased due to pine mortality, and subsoil organic matter
levels stabilized. This study emphasizes the importance of long-term experiments and
deep measurements when characterizing soil C and N responses to land use change and
the remarkable paucity of such long-term soil data deeper than 30 cm.
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https://hdl.handle.net/10161/21249Published Version (Please cite this version)
10.1111/gcb.12715Publication Info
Mobley, Megan L; Lajtha, Kate; Kramer, Marc G; Bacon, Allan R; Heine, Paul R; & Richter,
Daniel Deb (2015). Surficial gains and subsoil losses of soil carbon and nitrogen during secondary forest
development. Global change biology, 21(2). pp. 986-996. 10.1111/gcb.12715. Retrieved from https://hdl.handle.net/10161/21249.This is constructed from limited available data and may be imprecise. To cite this
article, please review & use the official citation provided by the journal.
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Show full item recordScholars@Duke
Daniel D. Richter
Professor in the Division of Earth and Climate Science
Richter’s research and teaching links soils with ecosystems and the wider environment,
most recently Earth scientists’ Critical Zone. He focuses on how humanity is transforming
Earth’s soils from natural to human-natural systems, specifically how land-uses alter
soil processes and properties on time scales of decades, centuries, and millennia.
Richter's book, Understanding Soil Change (Cambridge University Press), co-authored
with his former PhD

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