Format: ORAL

Ricardo Snchez-Martn1, Alicia Montesinos-Navarro1, Helga Ochoterena2, Irene Pisanty3, Mariana Rodrguez-Snchez2, Miguel Verd1, Hilda Flores-Olvera2

1 Centro de Investigaciones sobre Desertificación (CIDE-CSIC) Moncada (Valencia) Spain 2 Instituto de Biología, Universidad Nacional Autónoma de México, Ciudad de México, México 3 Facultad de Ciencias, Universidad Nacional Autónoma de México, Ciudad de México, México

Besides the environmental stress in arid and semi-arid regions, gypsum outcrops are a barrier to plant growth due to challenging soil nutrient levels. In such extreme conditions, biotic interactions are highly affected by species traits and micro environmental variability. Studies on facilitation have shown that nurse species alleviate abiotic stress for beneficiary species, but the impact of the micro-environmental variability generated by nurse plants in shaping facilitation outcomes is poorly understood. Here, we assess which traits define beneficiary species and whether nurse and non-nurse species differ in their ability to reduce abiotic stress and its variability under their canopy. We sampled recruits in two gypsum arid and stressful environments in the Cuatro Cinegas valley in Coahuila, Mexico. Our aims were to assess i) which species accumulate more juveniles beneath their canopy controlling for their coverage (nurse vs. non-nurse species); and ii) which species benefited from facilitation by determining whether they tend to recruit more species beneath or on the bare ground (beneficiary/non-beneficiary). Then, we compared how nurse and non-nurse species modify the physical and chemical microenvironments underneath their canopy, both in terms of magnitude and variation. Furthermore, comparisons were made between root growth, water retention, and nutrient accumulation in juvenile plants of beneficiary and non-beneficiary species. We found that facilitation is enhanced by species that provide a more homogeneous microenvironment rather than an intense reduction of microenvironmental stress under their canopy. In addition, the juveniles of beneficiary species invest more in root development, accumulate Ca and S in their shoot tissues, and show a higher water content than non-beneficiary species. Our results suggest that the homogeneity of microenvironments plays a crucial role in facilitative interactions, and the juveniles of beneficiary species show a less conservative strategy, investing more in resource acquisition than juveniles of non-beneficiary species.