Foliar nitrogen dynamics of an invasive legume compared to native non-legumes in fynbos riparian zones varying in water availability

  • Casparus J Crous 1. South African Environmental Observation Network, Arid Lands Node, P.O. Box 110040, Hadison Park 8306, Kimberley, South Africa; 2. Department of Conservation Ecology and Entomology, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa
  • Deanne C Drake Wisconsin Department of Natural Resources, USGS Upper Midwest Environmental Science Center, 2630 Fanta Reed Rd, La Crosse, WI, 54603, USA
  • Anna L Jacobsen Department of Biology, California State University, Bakersfield, 9001 Stockdale Hwy, Bakersfield, CA, 93311, USA
  • R Brandon Pratt Department of Biology, California State University, Bakersfield, 9001 Stockdale Hwy, Bakersfield, CA, 93311, USA
  • Shayne M Jacobs Department of Conservation Ecology and Entomology, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa
  • Karen J Esler 1. Department of Conservation Ecology and Entomology, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa; 2. Centre for Invasion Biology, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa
Keywords: δ15N, Acacia mearnsii, Black Wattle, South Africa, stable isotopes, water stress

Abstract

The legume Acacia mearnsii invades South Africa’s fynbos riparian zones and may alter the nitrogen (N) dynamics and supply in these areas that typically support few native N fixers. Nitrogen uptake by A. mearnsii may also be influenced by water availability, potentially affecting riparian-specific performance and impact estimations. We expected to find functional differences between the invasive legume and the two co-occurring but non-leguminous native species Brabejum stellatifolium and Metrosideros angustifolia. We also wanted to examine whether in-situ water availability affected N source or uptake in
the invasive species. We found A. mearnsii was indeed functioning differently from non-N-fixing native species, and had considerably higher foliar %N. Interestingly, 15N abundance and uptake were associated with site hydrology, meaning water availability should be scrutinised when assuming N-fixing in A. mearnsii using δ15N. Nonetheless, higher water availability to A. mearnsii in fynbos riparian ecosystems did increase foliar N uptake. This has implications for prioritizing clearing of sites with increased nutrient deposition, such as dense stands in relatively moist riparian zones.

Views
  • Abstract 70
  • PDF 33
Views and downloads are with effect from 11 January 2018
Published
2019-01-31
Section
Research paper