Fire legacies in eastern ponderosa pine forests.

Disturbance legacies structure communities and ecological memory, but due to increasing changes in disturbance regimes, it is becoming more difficult to characterize disturbance legacies or determine how long they persist. We sought to quantify the characteristics and persistence of material legacies (e.g.

Assessment of Selected Antibiotic Resistances in Ungrazed Native Nebraska Prairie Soils.

The inherent spatial heterogeneity and complexity of antibiotic-resistant bacteria and antibiotic resistance (AR) genes in manure-affected soils makes it difficult to sort out resistance that can be attributed to human antibiotic use from resistance that occurs naturally in the soil. This study characterizes native Nebraska prairie soils that have not been affected by human or food-animal waste products to provide data on background levels of resistance in southeastern Nebraskan soils. Soil samples were collected from 20 sites enumerated on tetracycline and cefotaxime media; screened for tetracycline-, sulfonamide-, β-lactamase-, and macrolide-resistance genes; and characterized for soil physical and chemical parameters.

Grassland productivity limited by multiple nutrients.

Terrestrial ecosystem productivity is widely accepted to be nutrient limited(1). Although nitrogen (N) is deemed a key determinant of aboveground net primary production (ANPP)(2,3), the prevalence of co-limitation by N and phosphorus (P) is increasingly recognized(4-8). However, the extent to which terrestrial productivity is co-limited by nutrients other than N and P has remained unclear.

Seasonal changes in depth of water uptake for encroaching trees Juniperus virginiana and Pinus ponderosa and two dominant C4 grasses in a semiarid grassland.

We used the natural abundance of stable isotopic ratios of hydrogen and oxygen in soil (0.05-3 m depth), plant xylem and precipitation to determine the seasonal changes in sources of soil water uptake by two native encroaching woody species (Pinus ponderosa P. & C.

Nitrogen mineralization dynamics in grass monocultures.

Although Wedin and Tilman (1990) observed large differences in in situ N mineralization among monocultures of five grass species, the mechanisms responsible were unclear. In this study, we found that the species did not change total soil C or N, and soil C: N ratio (range 12.9-14.

Species effects on nitrogen cycling: a test with perennial grasses.

To test for differing effects of plant species on nitrogen dynamics, we planted monocultures of five perennial grasses (Agropyron repens, Agrostis scabra, Poa pratensis, Schizachyrium scoparium, and Andropogon gerardi) on a series of soils ranging from sand to black soil. In situ net N mineralization was measured in the monocultures for three years. By the third year, initially identical soils under different species had diverged up to 10-fold in annual net mineralization.