Interactions Between Individual Plant Species and Soil Nutrient Status in Shortgrass Steppe

Abstract

Abstract. The effect of plant community structure on nutrient cycling is fundamental to our understanding of ecosystem function. We examined the importance of plant species and plant cover (i.e., plant covered microsites vs. bare soil) on nutrient cycling in shortgrass steppe of northeastern Colorado. We tested the effects of both plant species and cover on soils in an area of undisturbed shortgrass steppe and an area that had undergone nitrogen and water additions from 1971 to 1974, resulting in significant shifts in plant species composition.Soils under plants had consistently higher C and N mineralization rates and, in some cases, higher total and microbial C and N levels than soils without plant cover. Four native grasses, one sedge, and one shrub differed from one another in the quantity and quality of above-and belowground biomass but differences among the six species in soil nutrient cycling under their canopies were slight. However, soils under bunchgrasses tended to have higher C mineralization and microbial biomass C than soil under the rhizomatous grass, Agropyron smithii. Also, the one introduced annual in the study, Kochia scoparia, had soils with less plant-induced heterogeneity and higher rates of C and N mineralization as well as higher levels of microbial biomass C than soils associated with the other species. This species was abundant only on plots that had received water and nitrogen for a 4-yr period that ended 20 yr ago, where it has persisted in the absence of resource additions for 20 yr, suggesting a positive feedback between plant persistence and soil nutrient status.Plant cover patterns had larger effects on ecosystem scale estimates of soil properties than the attributes of a particular plant species. This result may be due to the semiarid nature of this grassland in which plant cover is discontinuous and decomposition and nutrient availability are primarily limited by water, not by plant species-mediated characteristics such as litter quality. That local plant-induced patterns in soil properties significantly affected ecosystem scale estimates of these properties indicates that consideration of structural attributes, particularly plant cover patterns, is critical to estimates of ecosystem function in shortgrass steppe.

The biology of Canadian weeds. 138. Kochia scoparia (L.) Schrad.

“…Although kochia can dominate semiarid or arid crop or ruderal areas of the western Great Plains of North America, it usually does not dominate natural ecosystems (Vinton and Burke 1995). Kochia growth, height, and architecture are markedly influenced by inter-and intraspecific competition; growth form ranges from erect, single-stemmed, and tall when growing with competing vegetation, to bushy and multi-branched when growing without such competition (Eberlein and Fore 1984; authors' personal observations).…”

“…The weed accumulates protein N within its tissue in direct proportion to the fertilizer rate applied (Steppuhn et al 1994). The chemical composition of kochia tissue favors microbial decomposition; the release of organic N maintains high N availability in soils beneath the weed (Vinton and Burke 1995). High N mineralization rates in kochia-infested areas are related to low root lignin:N and carbon:N ratios.…”

Inferences about winter temperatures and summer rains from the late Quaternary record of C4 perennial grasses and C3 desert shrubs in the northern Chihuahuan Desert

“…For example, establishment of woody desert shrubs can alter microclimate and soil properties beneath their canopies where litter and nutrients accumulate, providing favorable microsites for some species while depleting resources in intercanopy areas. The resulting microsite heterogeneity between canopy and intercanopy areas may in turn affect the composition and spatial distribution of species (Charley and West, 1977;Vinton and Burke, 1995). The progressive modernization of flora may have been due to such a feedback mechanism subsequent to mid-Holocene establishment of pioneer desert shrub species.…”

Soil Organic Matter Recovery in Semiarid Grasslands: Implications for the Conservation Reserve Program

“…All of the native and abandoned fields were dominated by perennial plants (D. P. Coffin, W. K. Lauenroth, and I. C. Burke, unpublished manuscript). Although there are slight differences among different perennial plant species in their soil nutrient accumulation patterns, those patterns are small compared to plant-interplant patterns (Vinton and Burke 1995), and our goal was to characterize systemlevel responses to cultivation and abandonment. We sampled at shallow depths because it is at these depths that we were most likely to capture recovery dynamics, given the organic matter distributions of these systems (Yonker et al 1988).…”