Resumen de The ecological significance of nutritional strategies in gypsum plant communit
Gypsophile species are edaphic endemics of gypsum soils, and they are considered specialists of this stressful substrate. Gypsum endemics from different families and regions of the world tend to show a unique leaf elemental composition, similar to the chemical characteristics of gypsum soils. However, the ecological significance of their unique foliar composition remains unknown. The factors underlying the ecological amplitude of gypsophiles remain also poorly studied. The main literature is based on the distribution of gypsophiles linked to gypsum soils in drylands, although some studies suggest a broader physiological amplitude depending on soil type, and a positive influence of disturbance. Therefore, I have assumed that gypsophiles have evolved in disturbed drylands with gypsum soils. In order to adapt to this combination of factors, I hypothesised that gypsophiles have become soil specialists with high capacity of nutrient uptake to be more competitive than other species in gypsum soils. To test this, we conducted a germination trial and a common garden experiment to analyse the ecological restriction of gypsophiles to different substrates, and to analyse the effect of different substrates on the whole-plant elemental composition of plants with contrasting affinity for gypsum soils. In the field, we studied the assemblage of plant communities under different grazing intensities on high gypsum soils, and whether the assembly of plant communities is mediated by any trait related to gypsum specialisation or herbivory resistance. Next, a browsing simulation was conducted to assess individual plant responses in calcic and gypsum pots. In addition, the variation of foliar and rhizospheric soil nutrient contents, and AM fungal colonisation were analysed throughout a year in the field to study the nutrient acquisition strategies of gypsophiles. The results obtained in this PhD thesis show that the fundamental niche of gypsophiles is not only explained by edaphic factors unique to gypsum soils, but seems to be related to alkaline soils with high calcium availability. When analysed under herbivory pressure, species with high gypsum affinity and increased foliar S content (i.e. gypsophiles) were more likely to assemble than other species. These gypsophiles were foliar accumulators of gypsum excess elements, even in calcic pots. They also seem to be adapted to P-scarcity by being less dependent on AMF symbiosis, and adjusting their acquisition strategies to nutrient pulses. Therefore, it seems that gypsophiles are specialists of gypsum soils to be more competitive in disturbed drylands through a unique nutritional strategy.
