Enhanced mycorrhization in four species of columnar cacti under the Sonoran Desert tree <em>Olneya tesota</em>

Abstract

Background: Columnar cacti survival in deserts occurs mainly under nurse plants, due to better conditions for germination and establishment, as greater humidity, and nutrient concentration. However, interactions like the association between arbuscular mycorrhizal fungi (AMF) and roots remain relatively unexplored. We evaluated the mycorrhizal status and soil rhizosphere properties of four columnar cacti species growing both under and outside their nurse plant. Hypotheses: Soil properties improvement under nurse plants has been correlated with the abundance of AMF. Therefore, a greater number of AMF structures and roots mycorrhization would be in facilitated plants, compared to the same species growing outside the nurse. Studied species: Nurse plant: Olneya tesota, facilitated species: Carnegiea gigantea, Pachycereus pringlei, Pachycereus schottii, and Stenocereus thurberi. Study site and dates: Central Gulf Coast subdivision of the Sonoran Desert, Sonora, Mexico; October 2020. Methods: Cacti roots and soil rhizosphere were collected under and outside the nurse plant. Roots were stained, and mycorrhizal colonization (MC), hairy roots (HR), visual density (VD), and number of spores were determined. Physicochemical soil properties were analyzed. Results: Values of MC, VD, spore number, organic matter (OM), nitrate, and total and assimilable phosphorous were higher under the nurse compared to bare areas. Conclusions: The hypothesis that mycorrhization parameters are greater in roots of cacti growing under the nurse was confirmed, besides previous knowledge about soil quality under nurse plants, suggesting that AMF play a significant role in the cacti facilitation process under nurses plants, and that nurse plant plays a significant role in AMF formation.