Humans have dramatically increased the deposition and availability of nutrients, such as nitrogen (N), worldwide. Soil organic matter (SOM) is a significant global reservoir of carbon (C); however, the effects of N enrichment on this large, heterogeneous C stock are unclear. Nitrogen has variable effects on the biological, chemical, and physical factors that determine SOM pool mean residence time; consequently, we predicted that N enrichment would have distinct effects on SOM pools, including the pool that is readily available for microbial decomposition, as well as the pools that have been stabilized against microbial decomposition via aggregate occlusion and mineral association. We addressed this gap in knowledge by measuring the effects of N addition on different SOM pools at five grassland experiments in the US Central Great Plains that participate in the Nutrient Network and have been fertilized for three or five years. Overall, N addition decreased microbial respiration of unoccluded OM by as much as 29 % relative to control plots, and consequently, decreased C loss from this pool. Furthermore, N addition tended to increase soil aggregation and C occlusion in large macro-aggregates. These results suggest that N addition will increase C sequestration by slowing the decomposition of SOM, as well as stabilizing SOM against microbial decomposition in aggregate-occluded pools. However, the effects of N on all pools studied varied among sites, possibly due to site variation in soil texture. Consequently, increased sequestration of soil C in response to N enrichment may not be universal across grasslands.
|Original language||English (US)|
|Number of pages||17|
|State||Published - Sep 22 2015|
Bibliographical noteFunding Information:
We thank Nutrient Network collaborators for establishing and maintaining the sites included in this study, including Elizabeth Borer, Adam Kay, and Eric Seabloom at Cedar Creek; Jean Knops at Cedar Point; Lori Biederman, Stan Harpole, Lauren Sullivan, and Ryan Williams at Chichaqua Bottoms; Kim LaPierre at Konza; and Dana Blumenthal, Cynthia Brown, and Julia Klein at Shortgrass Steppe. Numerous individuals at the University of Minnesota and Iowa State University assisted us in the lab and field, including: Daniel Ackerman, Rick Beckel, Chris Buyarski, Katie Kemmitt, Joey Krenz, Eric Lind, Elyssa McFarland, Queenster Nartey, Jennifer Pederson, Kristen Peterson, Missy Rudeen, Kelsey Thurow, and Michael Wells. Eric Lind also provided valuable assistance with data analysis and Nutrient Network database management. This work was supported by the Cedar Creek Long Term Ecological Research Program (NSF DEB-1234162), a National Science Foundation Graduate Research Fellowship to CER (Grant No. 00039202), and the Dayton Fund of the Bell Museum of Natural History. The Nutrient Network has been supported by funding to Elizabeth Borer and Eric Seabloom from the National Science Foundation Research Coordination Network and the Long Term Ecological Research programs, as well as the University of Minnesota’s Institute on the Environment.
© 2015, Springer International Publishing Switzerland.
- Microbial respiration
- Nutrient Network
- Soil aggregate
- Wet sieving