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International audience; Perennial grasses are the main source of fuel during fires in savannas. The demography of these grasses likely varies between species although they have the same general architecture and coexist in savannas. However, very few studies compare their demography. Similarly, their demography likely varies between years because of the variability in weather condition and fire intensity. We described and compared the demography and life-cycle of the four dominant perennial grass species (Andropogon canaliculatus, Andropogon schirensis, Hyparrhenia diplandra and Loudetia simplex) of the Lamto savanna (Ivory Coast) and assessed the influence of their demographic features (stasis, fecundity, growth, fragmentation and retrogression) on this demography. Grass species were monitored over three consecutive years (2015-2016, 2016-2017 and 2017-2018) on three 5 m × 10 m plots. We used a size-classified matrix model with 5 circumference classes (3-10 cm, 10-20 cm, 20-35 cm, 35-50 cm and >50 cm). Results showed differences in the age-based parameters, asymptotic growth rates (λs) and elasticities of the λs of the grass species. The population of A. canaliculatus, A. schirensis and H. diplandra were slowly declining while L. simplex was significantly declining. There were noticeable year-to-year variations in the demography of these four species. The most important demographic parameter influencing λs was the stasis in all species, while retrogression and fragmentation contributed to a relative homogeneity of ages between size-classes 2 to 5. This study provides new insights about the demography of Guinean savanna grasses that could be used to describe the mechanisms of their coexistence, and inform fire management policies.

International audience; Biological nitrification inhibition (BNI) has already led to several studies mainly focused on underlying molecular mechanisms and applications to agriculture. We argue that it is also important to study BNI more systematically from the ecological and evolutionary points of view to understand its implications for plants and soil nitrifiers as well as its consequences for ecosystems. Therefore, we propose here a dedicated research agenda identifying the most critical research questions: (1) How is BNI distributed across plant phylogeny and why has it been selected? (2) What are the costs-to-benefits balance of producing BNI compounds and the relative impacts on BNI evolution? (3) Can we understand the evolutionary pressures leading to BNI and identify the environmental conditions favorable to BNI plants? (4) How has BNI coevolved with plant preference for ammonium vs. nitrate? (5) Diverse BNI compounds and various inhibition mechanisms have been described, but implications of this diversity are not understood. Does it allow inhibition of various groups of nitrifiers? (6) Does this diversity of BNI compounds increase the efficiency, spatial extension, and duration of BNI effect? (7) What are the impacts of BNI compounds on other soil functions? (8) Can field experiments, coupled to scanning of the diversity of BNI capabilities within plant communities, evaluate whether BNI influences plant-plant competition and plant coexistence? (9) Can field quantification of various nitrogen (N) fluxes assess whether BNI lead to more efficient N cycling with lower losses and hence increased primary production? (10) Can the impact of BNI on N budgets and climate (through its impact on N2O emissions and its indirect impact on carbon budget) be evaluated at the regional scale? We discuss why implementing this research program is crucial both for the sake of knowledge and to develop applications of BNI for agriculture.