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Competition and coexistence of savanna plants in relation to phosphorus and different forms of nitrogen

par Sanvito, Emilie
Promoteur Olde Venterink, H
Co-Promoteur Lannes, Luciola S.
Publication Non publié, 2024-08-28

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Résumé :

In savanna ecosystems, where nitrogen and phosphorus are often (co-)limited, these nutrients influence competition and coexistence between species. Studies suggest that the coexistence between trees and grasses in savannas is influenced by N form partitioning, where the two functional groups prefer distinct N forms. Similarly, N form partitioning might affect the coexistence of invasive and native species in the Brazilian Cerrado. To investigate this, I present two mesocosm fertilization experiments. One with African savanna trees and grasses, to examine N form uptake and how competition affects this. The other with common Cerrado species, to examine N form uptake and the effect of phosphorus fertilization on the community. Using 15N-labelled and unlabelled N forms, applied in pulses 24 hours before harvest, plant biomass was analysed for δ15N. Results show no significant differences in N form uptake among species, indicating that N form partitioning does not stabilise the species coexistence in the Cerrado or the African savanna. However, Sporobolus indicus (African savanna grass) was a superior competitor for nitrate compared to the two tree species Vachellia polycantha and Dichrostachys cinerea. In the Cerrado experiment differences in total N uptake were observed, with high and low N uptake groups. Additionally, phosphorus fertilization influenced community composition of the Cerrado experiment, with invasive species becoming more dominant. The findings of this study highlight that while N form partitioning may not be a stabilizing mechanism for species coexistence in savannas, nutrients like nitrogen and phosphorus still play a crucial role in the competitive interactions of species.