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Original Articles

Effects of recent fire on soil conditions and nutrient use of a native and an invasive grass in the Brazilian savanna

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Pages 359-370 | Received 13 Apr 2019, Accepted 27 Apr 2019, Published online: 26 May 2019
 

ABSTRACT

In fire-influenced savanna ecosystems, native and invasive exotic plants may use different abilities to coexist and compete for nutrients available in post-fire soil. The availability and uptake of nitrate by two C4 grasses (Urochloa brizantha (exotic invasive) and Axonopus siccus (native)) were characterized in an unburned area and in a recently burned area in the Cerrado of Southeastern Brazil. Ecophysiologic tests were performed to measure Nitrate Reductase Activity (NRA) and nitrate content in leaves and roots. Soil fertility was also analyzed. In the unburned area, organic matter (25.3 ± 2.4 g kg−1), phosphorus (19.0 ± 2.0 mg dm−3), and nitrate (19.9 ± 7.4 mg dm−3) levels were higher than in the recently burned area, which had 27% less cations in the soil. In comparison with soils from the recently burned and unburned areas, ashes of the recently burned area had higher pH, electrical conductivity and nitrate, potassium, and calcium contents. In both areas, the aboveground part of U. brizantha was more responsive to nitrate compared to A. siccus and both had low belowground NRA. This confirms the working hypothesis that the two species undergo distinct ecophysiologic processes and indicate the adaptive potential of U. brizantha to bypass soil nutrient limitation.

RÉSUMÉ

Dans les écosystèmes de savanes influencés par les feux, les plantes indigènes et exotiques peuvent utiliser différentes habiletés pour coexister et se faire compétition pour les nutriments disponibles dans le sol suite au feu. La disponibilité et l’absorption de nitrate par deux graminées C4 (Urochloa brizantha (exotique invasive) and Axonopus siccus (indigène)) ont été caractérisées dans une zone non brûlée et dans une zone récemment brûlée du Cerrado du sud-est du Brésil. Des tests écophysiologiques ont été réalisés pour mesurer l’activité de la nitrate réductase (NRA) et le contenu en nitrate dans les feuilles et les racines. La fertilité du sol a aussi été analysée. Les niveaux de matière organique (25.3 ± 2.4 g kg−1), de phosphore (19.0 ± 2.0 mg dm−3) et de nitrate (19.9 ± 7.4 mg dm−3) étaient plus élevés dans la zone non brûlée que dans la zone récemment brûlée, qui avait 27% moins de cations dans le sol. La cendre de la zone récemment brûlée avait un pH, une conductivité électrique et des contenus en nitrate, potassium et calcium plus élevés que les sols des zones non brûlée et récemment brûlée. Dans les deux zones, les parties aériennes de U. brizantha répondaient davantage au nitrate comparativement à A. siccus et les deux espèces avaient de faibles NRA dans les parties souterraines. Cela confirme l’hypothèse que les deux espèces utilisent des processus écophysiologiques distincts, en plus d’indiquer le potentiel adaptatif de U. brizantha de contourner la limitation en nutriments dans le sol.

Acknowledgments

The authors thank the anonymous reviewer of Peerage of Science and Dr. Hugo Asselin, who contributed in a constructive way to this work.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

CAPES/Brazil (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) provided a postdoctoral scholarship (process BEX1059/10-6). CAPES-SwB/Brazil (Programa Ciências sem Fronteiras) also provided a postdoctoral scholarship (process 0576/2013 – project ‘Desenvolvimento de estraté gias de restauração em savanas tropicais – o caso do Cerrado’). CAPES-DGPU/Brazil also provided financial support (process 1696/2015 – project ‘Restauração de ecossistemas savânicos: princípios e práticas’).

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