Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 31, 2001
Publication Date: N/A
Interpretive Summary: Bunchgrasses (plants with many stems compactly arranged) accumulate carbon and nitrogen in soils only beneath plants as they do not possess belowground stems, while rhizomatous grasses (plants with stems widely spaced) accumulate nutrients in soils and in rhizomes (belowground stems). These differences in accumulation of belowground nutrients may explain why bunchgrasses dominate dry grasslands and rhizomatous grasses dominate wet grasslands. Contrary to this, however, bunchgrasses accumulated more carbon and nitrogen in soils than rhizomatous grasses did in rhizomes and soils in the wet grassland while the opposite occurred in the dry grassland. Light availability is more important than accumulation of soil nutrients in wet grasslands as the wide spacing of stems in rhizomatous grasses is more beneficial for light capture than the compact arrangement in bunchgrasses. In contrast, soil nutrients are limiting in dry grasslands, rather than light, and greater carbon and nitrogen in soils directly beneath bunchgrasses is ecologically advantageous.
We compared belowground soil organic carbon (SOC) and total nitrogen (N) accumulation between caespitose and rhizomatous perennial grasses in grazed and ungrazed sites in semiarid and mesic communities in the Great Plains. Caespitose grasses accumulated substantially greater pools of SOC and N in soils than rhizomatous grasses accumulated in rhizomes. SOC and N pools beneath caespitose clones exceeded combined (soil + rhizome) pools for rhizomatous grasses for all but the smallest clones (<90 cm2 basal area) in the mesic community, but were smaller at all basal areas in the semiarid community. Prevailing environmental conditions influenced belowground nutrient accumulation beneath caespitose grasses as soil nutrient pools were 40 to 50% lower in the semiarid than the mesic community, while combined nutrient pools beneath the rhizomatous species were relatively constant in both communities. Comparative evaluation of belowground carbon and nitrogen accumulation in caespitose and rhizomatous grasses along a productivity gradient was unsuccessful in providing consistent differences to ascertain a greater functional understanding of the relative distribution of these two growth forms. The alternative explanation for the observation that caespitose and rhizomatous grasses dominate semiarid and mesic grasslands, respectively, is that plant-soil interactions are influenced by different constraints along productivity gradients; light in mesic environments and soil nutrients in semiarid environments. Therefore, accumulation of soil nutrients beneath plants appears to be ecologically advantageous only for caespitose grasses in low productivity sites.