Understanding how the network structure of plant and microbiota interactions differ along ecological gradients is of great interest. We studied network patterns at 60 sites across the Tibetan Plateau, representing a gradient in both precipitation and plant species richness. The number of fungal OTUs that were uniquely connected to each plant species in the plant-fungi network was most strongly positively related to plant species richness. By contrast, the number of unique bacterial OTUs linked to each plant species decreased with increasing plant species richness. The number of fungal OTUs specifically linked to each plant species was positively related to plant species richness, and to productivity. We suggest that in a more extreme high-stress environment that decreases plant species richness, plants and fungi have fewer excess resources to invest in specific relationships, showing up as lower associated microbiome richness, with bacteria may partially replacing this role in high stress/low productivity environments.