Plant and soil 15N Isotope data
A key question in savanna ecology is how trees and grasses coexist under N limitation. We used 15N sable isotopes and N content to study nitrogen source partitioning across seasons from trees and associated grasses in a semi- arid savanna. We also used 15N tracer additions to investigate possible redistribution of N by trees to grasses. Foliar stable N isotope ratio (δ15N) values were consistent with trees and grasses using mycorrhiza-supplied N in all seasons except in the wet season when they switched to microbially fixed N. The dependence of trees and grasses on mineralized soil N seemed highly unlikely based on seasonal variation in mineralization rates in the Kruger Park region. Remarkably, foliar δ15N values were similar for all three tree species differing in the potential for N fixation through nodulation. The tracer experiment showed that N was redistributed by trees to understory grasses in all seasons. Our results suggest that the redistribution of N from trees to grasses and uptake of N was independent of water redistribution. Although there is overlap of N sources between trees and grasses, dependence on biological sources of N coupled with redistribution of subsoil N by trees may contribute to the coexistence of trees and grasses in semi-arid savannas.
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This data is collected in Andover Game Reserve, South Africa. It comprises natural abundance of nitrogen stable isotopes in grass and trees, and 15N tracer data applied seasonally to determine nitrogen movement from soil to the plants. The tracer was applied at 2.5m depths. This data is part of a published paper with doi:10.1007/s00442-013-2848-8. It contains two worksheets with plant and soil data. The paper which is published using this data is "Overlap in nitrogen sources and redistribution of nitrogen between trees and grasses in a semi‑arid savanna" by Priyadarshini et al. 2014. Oecologia 174: 1107-1116. The link to the paper is given below in the related links column. We determined nitrogen movement from deep soil to tree and to grasses via tree redistribution. We also showed that tree and grasses in this site seemed to use mycorrhizal supplied nitrogen for most part of the year and both did not rely on soil mineralized nitrogen.