Individual-plant scale patterns of roots and soil resources in shortgrass steppe

I evaluated relationships between the distribution and morphology of Bouteloua gracilis plants and heterogeneity of soil water, organic matter, and nitrogen in shortgrass steppe. My primary objective was to explain the spatial scales of strong neighbor interference and gap dynamics in terms of soil water dynamics, root distribution, and plant spacing. I also tested the hypothesis that sparse bunchgrass cover is associated with soil heterogeneity at the scale of individual plants and interspaces.; Spatial patterns of soil water were consistent with scales of resource preemption and gap dynamics estimated previously from population and community level data. Soil water was removed rapidly from typical interspaces in which adult plants greatly restrict seedling establishment (10-20 cm diameter) and slowly from openings large enough to initiate gap dynamics ({dollar}>{dollar}50 cm). Although openings over 5 cm across represented 34% of the area, only 0.5% of the area was beyond the range of B. gracilis roots and only 1-4% of the area was at distances from tillers associated with low root biomass and relatively high soil water availability.; In the field, uptake of water was concentrated in a core area much smaller than the extent of a plant's root system (about 10 vs. 30 cm radius), suggesting that morphological constraints limited exploitation of resources in outer portions of root systems. Under controlled conditions, however, B. gracilis showed a high capacity to adjust fine root distribution to exploit water at distances greater than 10 cm from tillers. The role and scale of root system plasticity in the field need clarification.; Total and biologically active soil organic matter (0-5 cm depth) were more abundant under individual B. gracilis plants than in interspaces. Total and mineralizable N and C, the fraction of organic C respired, and ratio of respiration to N mineralization were significantly greater for soil under plants.; Results were consistent with hypotheses that in shortgrass steppe (1) an important component of resource heterogeneity is scaled to the limited belowground zone of resource preemption of dominant bunchgrasses and (2) patchy growth of bunchgrasses generates strong heterogeneity of ecosystem properties. Results illustrate the importance of morphology of the dominant species to higher level ecological phenomena in a semiarid grassland.