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We present a conceptual model in which plant—soil interactions in grasslands are characterized by the extent to which water is limiting. Plant—soil interactions in dry grasslands, those dominated by water limitation (‘lowground-dominance’), are fundamentally different from plant—soil interactions in subhumid grasslands, where resource limitations vary in time and space among water, nitrogen, and light (‘indeterminate dominance’). In the belowgrounddominance grasslands, the strong limitation of soil water leads to complete (though uneven) occupation of the soil by roots, but insufficient resources to support continuous aboveground plant cover. Discontinuous aboveground plant cover leads to strong biological and physical forces that result in the accumulation of soil materials beneath individual plants in resource islands. The degree of accumulation in these resource islands is strongly influenced by plant …