TY - JOUR
T1 - Variability in Soil Nitrogen Retention Across Forest, Urban, and Agricultural Land Uses
AU - Weitzman, Julie N.
AU - Kaye, Jason P.
N1 - Funding Information:
We thank Rachel Brimmer, Sara Eckert, and the undergraduate assistants in the Kaye Biogeochemistry Lab at Penn State University for their assistance in sample collection. This project was funded by the National Science Foundation under Grant No. DEB 0816668. JNW also received support from the USDA-NIFA predoctoral fellowship program (2015-67011-22796).
Publisher Copyright:
© 2016, Springer Science+Business Media New York.
PY - 2016/12/1
Y1 - 2016/12/1
N2 - In regions of mixed land use, some ecosystems are sinks for N pollution and others are sources. Yet, beyond this gross characterization, we have little understanding of how adjacent land-use types vary in mechanisms of N cycling and retention. This study assessed the rate and magnitude of soil N retention pathways in forest, urban, and agricultural ecosystems. Soil plots in each land use were labeled with inorganic 15N and cored at 15 min, 2 days, and 20 days following injection. Subsamples were biologically fractionated to differentiate labile and stable pools, while gross N transformations were assessed via the 15N isotope dilution method. Stable soil organic 15N formed rapidly (within 15 min) in all land uses when added as 15NH4 +, and became a proportionally larger sink for inorganic 15N over time. Forests had the lowest gross immobilization rates, but the greatest amount of stable N formation. Rapid retention of NH4 + in forests may be driven by abiotic processes, with root uptake becoming a more important mechanism of retention over time. Urban sites, on the other hand, had the highest gross microbial immobilization rates and highest root N uptake, suggesting that high short-term N retention may be due to rapid biological processing. Agricultural systems, with low root uptake and the lowest stable N formation, had little capacity for retention of added N. These apparently distinct land-use cases can be understood by synthesizing several emerging aspects of N retention theory that (1) distinguish kinetic and capacity N saturation, (2) recognize links between soil C saturation on minerals and N retention, and (3) account for rapid transfers of NH4 + to stable organic pools.
AB - In regions of mixed land use, some ecosystems are sinks for N pollution and others are sources. Yet, beyond this gross characterization, we have little understanding of how adjacent land-use types vary in mechanisms of N cycling and retention. This study assessed the rate and magnitude of soil N retention pathways in forest, urban, and agricultural ecosystems. Soil plots in each land use were labeled with inorganic 15N and cored at 15 min, 2 days, and 20 days following injection. Subsamples were biologically fractionated to differentiate labile and stable pools, while gross N transformations were assessed via the 15N isotope dilution method. Stable soil organic 15N formed rapidly (within 15 min) in all land uses when added as 15NH4 +, and became a proportionally larger sink for inorganic 15N over time. Forests had the lowest gross immobilization rates, but the greatest amount of stable N formation. Rapid retention of NH4 + in forests may be driven by abiotic processes, with root uptake becoming a more important mechanism of retention over time. Urban sites, on the other hand, had the highest gross microbial immobilization rates and highest root N uptake, suggesting that high short-term N retention may be due to rapid biological processing. Agricultural systems, with low root uptake and the lowest stable N formation, had little capacity for retention of added N. These apparently distinct land-use cases can be understood by synthesizing several emerging aspects of N retention theory that (1) distinguish kinetic and capacity N saturation, (2) recognize links between soil C saturation on minerals and N retention, and (3) account for rapid transfers of NH4 + to stable organic pools.
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U2 - 10.1007/s10021-016-0007-x
DO - 10.1007/s10021-016-0007-x
M3 - Article
AN - SCOPUS:84975263505
VL - 19
SP - 1345
EP - 1361
JO - Ecosystems
JF - Ecosystems
SN - 1432-9840
IS - 8
ER -