Abstract
Here we aim to demonstrate that in arid environments the competitive balance between species can be determined by niche separation with either nitrogen or water as the relevant niche axis. To do this we sampled roots <2 mm in diameter for 5 soil pits equidistant between two coexisting species, a shrub and a grass. Using stable carbon and nitrogen isotope ratios of fine roots we determine both photosynthetic pathway and rooting depth. We also examine the distribution of soil moisture and nitrogen relative to root biomass. Our results for root biomass and stable isotope ratios of fine roots demonstrate both niche separation and competition for resources. Root biomass is highest at the top of the profile where soil nitrogen is highest and soil moisture is lowest. We conclude that while there is competition for resources in the middle of the profile, competition is mitigated by photosynthetic pathway. The facultative CAM shrub grows whenever the soil at the surface is wet enough. The C4 photosynthetic pathway of the grass is more nitrogen and water use efficient making it better adapted to the low nitrogen in the middle of the profile and low summer rainfall.
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Acknowledgements
Funding from BIOTA Southern Africa sponsored by the German Federal Ministry of Education and Research under promotion number 01 LC 0024A is acknowledged. February acknowledges funding from both the South Africa NRF as well as the Mellon Foundation. Mr Christo Visser very kindly allowed us to conduct this research on his farm. Corli Coetsee and Stephan Woodbourne made suggestions on improving the manuscript.
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February, E.C., Allsopp, N., Shabane, T. et al. Coexistence of a C4 grass and a leaf succulent shrub in an arid ecosystem. The relationship between rooting depth, water and nitrogen. Plant Soil 349, 253–260 (2011). https://doi.org/10.1007/s11104-011-0867-y
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DOI: https://doi.org/10.1007/s11104-011-0867-y