TY - JOUR
T1 - Spatial variation of the stable nitrogen isotope ratio of woody plants along a topoedaphic gradient in a subtropical savanna
AU - Bai, Edith
AU - Boutton, Thomas W.
AU - Liu, Feng
AU - Wu, X. Ben
AU - Archer, Steven R.
AU - Hallmark, C. Thomas
N1 - Funding Information:
Acknowledgments This work was supported by the NSF Ecosystem Studies Program (DEB-9981723). We are grateful to Kirk Jessup, Lisa Alexander, Donna Prochaska, Terri Rosol, Andrew Boutton, and Heather Jahnsen for assistance with field work and laboratory analyses. We thank Drs Benjamin Z. Houlton and Fred E. Smeins whose constructive comments helped improve the manuscript. Thanks are also extended to David McKown, manager of the La Copita Research Area, for assistance with on-site logistics.
PY - 2009/3
Y1 - 2009/3
N2 - Variation in the stable N isotope ratio (δ15N) of plants and soils often reflects the influence of environment on the N cycle. We measured leaf δ15N and N concentration ([N]) on all individuals of Prosopis glandulosa (deciduous tree legume), Condalia hookeri (evergreen shrub), and Zanthoxylum fagara (evergreen shrub) present within a belt transect 308 m long × 12 m wide in a subtropical savanna ecosystem in southern Texas, USA in April and August 2005. Soil texture, gravimetric water content (GWC), total N and δ15N were also measured along the transect. At the landscape scale, leaf δ15N was negatively related to elevation for all the three species along this topoedaphic sequence. Changes in soil δ15N, total N, and GWC appeared to contribute to this spatial pattern of leaf δ15N. In lower portions of the landscape, greater soil N availability and GWC are associated with relatively high rates of both N mineralization and nitrification. Both soil δ15N and leaf [N] were positively correlated with leaf δ15N of non-N2 fixing plants. Leaf δ15N of P. glandulosa, an N2-fixing legume, did not correlate with leaf [N]; the δ15N of P. glandulosa's leaves were closer to atmospheric N2 and significantly lower than those of C. hookeri and Z. fagara. Additionally, at smaller spatial scales, a proximity index (which reflected the density and distance of surrounding P. glandulosa trees) was negatively correlated with leaf δ15N of C. hookeri and Z. fagara, indicating the N2-fixing P. glandulosa may be important to the N nutrition of nearby non-N2-fixing species. Our results indicate plant 15N natural abundance can reflect the extent of N retention and help us better understand N dynamics and plant-soil interactions at ecosystem and landscape scales.
AB - Variation in the stable N isotope ratio (δ15N) of plants and soils often reflects the influence of environment on the N cycle. We measured leaf δ15N and N concentration ([N]) on all individuals of Prosopis glandulosa (deciduous tree legume), Condalia hookeri (evergreen shrub), and Zanthoxylum fagara (evergreen shrub) present within a belt transect 308 m long × 12 m wide in a subtropical savanna ecosystem in southern Texas, USA in April and August 2005. Soil texture, gravimetric water content (GWC), total N and δ15N were also measured along the transect. At the landscape scale, leaf δ15N was negatively related to elevation for all the three species along this topoedaphic sequence. Changes in soil δ15N, total N, and GWC appeared to contribute to this spatial pattern of leaf δ15N. In lower portions of the landscape, greater soil N availability and GWC are associated with relatively high rates of both N mineralization and nitrification. Both soil δ15N and leaf [N] were positively correlated with leaf δ15N of non-N2 fixing plants. Leaf δ15N of P. glandulosa, an N2-fixing legume, did not correlate with leaf [N]; the δ15N of P. glandulosa's leaves were closer to atmospheric N2 and significantly lower than those of C. hookeri and Z. fagara. Additionally, at smaller spatial scales, a proximity index (which reflected the density and distance of surrounding P. glandulosa trees) was negatively correlated with leaf δ15N of C. hookeri and Z. fagara, indicating the N2-fixing P. glandulosa may be important to the N nutrition of nearby non-N2-fixing species. Our results indicate plant 15N natural abundance can reflect the extent of N retention and help us better understand N dynamics and plant-soil interactions at ecosystem and landscape scales.
KW - Dinitrogen fixation
KW - Nitrogen availability
KW - Nitrogen cycling
KW - Nitrogen isotope discrimination
KW - Spatial scale
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U2 - 10.1007/s00442-008-1246-0
DO - 10.1007/s00442-008-1246-0
M3 - Article
C2 - 19085012
AN - SCOPUS:60449112153
SN - 0029-8549
VL - 159
SP - 493
EP - 503
JO - Oecologia
JF - Oecologia
IS - 3
ER -