Patterns and Drivers of Plant Arbuscular Mycorrhizal Traits Across a Pedo-Climatic Gradient in Mediterranean Agroecosystems Under Desertification Risk

Desertification is a global concern, reducing vegetation cover and soil fertility. Arbuscular mycorrhizal symbiosis (AM), the most common plant-fungi association, can enhance plant fitness and stress tolerance. Despite its significance, comprehensive data on community-wide patterns and drivers of plant AM traits are limited in the Mediterranean, one of the regions most vulnerable to desertification. We examined four traits: colonization frequency, intensity, arbuscule abundance, and spore density in the rhizosphere of 20 plant species across ten agroecosystems in desertification-prone areas of Italy, Spain, and Portugal. We analysed whether these traits varied across Raunkiær’s plant life forms and were affected by vegetation cover, soil properties, precipitation, and temperature, both overall and regionally, to explore potential context-dependency. All plants showed a high frequency of AMF colonization, with an average intensity of 54%, indicating obligate AMF interactions, and arbuscule abundance was significantly correlated with spore density. These traits were significantly higher in microhabitats dominated by trees and shrubs compared to those dominated by herbaceous plants. Phanerophytes (perennials) presented lower trait values than therophytes (annuals), while the highest values were found in hemicryptophytes. Lampedusa, a region with hotter and drier climate conditions in Southern Europe, had significantly lower AMF trait levels, though Spanish site values resembled those in Sicily more than Portugal. Soil organic carbon, nitrogen, and the overall positive interaction between precipitation and temperature significantly influenced all AMF traits. However, the magnitude and direction of soil and climate related effects differed among regions, indicating strong context dependency. Our study contributes to better define indicators for monitoring desertification and evaluating restoration efforts while highlighting the need of site-specific evaluations and careful interpretation of broad generalisations.