Antarctica harbors some of the most extreme ecosystems on earth, where only two vascular plants persist. The native grass Deschampsia antarctica provides a model for plant-microbe interactions under intense abiotic stress. We present the first multi-compartmental and multi-kingdom characterization of bacterial and fungal communities associated with D. antarctica across three South Shetland Islands. Metabarcoding revealed strong compartmentalization: the rhizosphere displayed the highest richness and complex bacterial-fungal networks; the root endosphere showed intermediate diversity with keystone taxa such as Rhizobiales and Streptomyces;" and the leaf endosphere was simplified, dominated by stress-tolerant taxa including Pseudomonas and Helotiales. Despite marked soil heterogeneity, phosphorus enrichment at Admiralty Bay, base cations at Coppermine Cove, and iron at Byers Peninsula, a conserved core (20 bacterial and 5 fungal genera) persisted, mainly cold-adapted saprotrophs and plant-associated taxa. Fungal assemblages were more responsive to soil chemistry, with site-specific enrichments such as Zymoseptoria and Herpotrichia. Overall, D. antarctica holobionts exhibited a dual strategy: conserved microbial backbones confer stability, while localized assemblages shaped by soil chemistry and geography enhance adaptability. Together, these findings provide one of the most integrative characterizations of the D. antarctica holobiont to date, revealing how conserved and adaptive microbial components support plant resilience under extreme Antarctic conditions and offering valuable insights for predicting biological responses to ongoing climate change."