title: Nitrogen-mediated effects of elevated CO2on intra-aggregate soil pore structure.
abstract: Soil pore structure has a strong influence on water retention, and is itself influenced by plant and microbial dynamics such as root proliferation and microbial exudation. Although increased nitrogen (N) availability and elevated atmospheric CO2concentrations (eCO2) often have interacting effects on root and microbial dynamics, it is unclear whether these biotic effects can translate into altered soil pore structure and water retention. This study was based on a long-term experiment (7 yr at the time of sampling) in which a C4pasture grass (Paspalum notatum) was grown on a sandy loam soil while provided factorial additions of N and CO2. Through an analysis of soil aggregate fractal properties supported by 3D microtomographic imagery, we found that N fertilization induced an increase in intra-aggregate porosity and a simultaneous shift toward greater accumulation of pore space in larger aggregates. These effects were enhanced by eCO2and yielded an increase in water retention at pressure potentials near the wilting point of plants. However, eCO2alone induced changes in the opposite direction, with larger aggregates containing less pore space than under control conditions, and water retention decreasing accordingly. Results on biotic factors further suggested that organic matter gains or losses induced the observed structural changes. Based on our results, we postulate that the pore structure of many mineral soils could undergo N-dependent changes as atmospheric CO2concentrations rise, having global-scale implications for water balance, carbon storage, and related rhizosphere functions.
authors.affiliation: Department of Environmental Sciences, Rutgers, The State University of New Jersey, 14 College Farm Road, New Brunswick, New Jersey, 19010, USA.
authors.forename: Joshua S
authors.identifier: 0000-0003-4624-2956
authors.initials: JS
authors.lastname: Caplan
authors.affiliation: Department of Environmental Sciences, Rutgers, The State University of New Jersey, 14 College Farm Road, New Brunswick, New Jersey, 19010, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Giménez
authors.affiliation: Department of Environmental Sciences, Rutgers, The State University of New Jersey, 14 College Farm Road, New Brunswick, New Jersey, 19010, USA.
authors.forename: Vandana
authors.initials: V
authors.lastname: Subroy
authors.affiliation: School of Environmental Sciences, University of Guelph, 50 Stone Road East, Guelph, Ontario, N1G 2W1, Canada.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Heck
authors.affiliation: US Department of Agriculture, Agricultural Research Service, National Soil Dynamics Laboratory, 411 South Donahue Drive, Auburn, Alabama, 36832, USA.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Prior
authors.affiliation: US Department of Agriculture, Agricultural Research Service, National Soil Dynamics Laboratory, 411 South Donahue Drive, Auburn, Alabama, 36832, USA.
authors.forename: G Brett
authors.initials: GB
authors.lastname: Runion
authors.affiliation: US Department of Agriculture, Agricultural Research Service, National Soil Dynamics Laboratory, 411 South Donahue Drive, Auburn, Alabama, 36832, USA.
authors.forename: H Allen
authors.initials: HA
authors.lastname: Torbert
mesh_terms: D002244:Carbon; D002245:Carbon Dioxide; D009584:Nitrogen / Q000737:chemistry*; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology
chemical_list: D012987:Soil; D002245:Carbon Dioxide; D002244:Carbon; D009584:Nitrogen
keywords: Paspalum notatum (bahiagrass); X-ray computed microtomography; elevated carbon dioxide; fractal dimension of mass; intra-aggregate pores; nitrogen fertilization; soil structure; water retention