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Phosphorus (P) has been proposed to directly limit primary productivity in some temperate grassland ecosystems. Our study of a recovering prairie on Colorado's Front Range suggests that P availability, possibly via regulation of nitrogen (N) fixation, may strongly influence N availability in recovering prairie soils. Consequently, increased P availability could indirectly affect plant growth through the alleviation of N limitation. At our site, concentrations of soil inorganic N were nearly three times higher in plots fertilized with P than in control plots. Subsequent acetylene reduction analyses showed that soil N fixation rates were more than double for P fertilization plots. These results highlight potential...
Temperate and boreal forest ecosystems contain a large part of the carbon stored on land, in the form of both biomass and soil organic matter. Increasing atmospheric [CO2], increasing temperature, elevated nitrogen deposition and intensified management will change this C store. Well documented single-factor responses of net primary production are: higher photosynthetic rate (the main [CO2] response); increasing length of growing season (the main temperature response); and higher leaf-area index (the main N deposition and partly [CO2] response). Soil organic matter will increase with increasing litter input, although priming may decrease the soil C stock initially, but litter quality effects should be minimal (response...
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Establishment of native plant populations on disturbed roadsides was investigated at Bryce Canyon National Park (BCNP) in relation to several revegetation and seedbed preparation techniques. In 1994, the BCNP Rim Road (2,683?2,770 m elevation) was reconstructed resulting in a 23.8-ha roadside disturbance. Revegetation comparisons included the influence of fertilizer on plant establishment and development, the success of indigenous versus commercial seed, seedling response to microsites, methods of erosion control, and shrub transplant growth and survival. Plant density, cover, and biomass were measured 1, 2, and 4 years after revegetation implementation (1995?1998). Seeded native grass cover and density were the...
We tested the effects of plant species, fertilization and elevated CO2 on water-stable soil aggregation. Five annual grassland species and a plant community were grown in outdoor mesocosms for 4 years, with and without NPK fertilization, at ambient or elevated atmospheric CO2 concentrations. Aggregate stability (resistance of aggregates to slaking) in the top 0.15 m of soil differed among plant species. However, the more diverse plant community did not enhance aggregate stability relative to most monocultures. Species differences in aggregate stability were positively correlated with soil active bacterial biomass, but did not correlate with root biomass or fungal length. Plant species did not affect aggregate stability...
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In order to determine the effect of increased nitrogen inputs on fluxed of N2O and CH4 from alpine soils, we measured fluxes of these gases from fertilized and unfertilized soils in wet and dry alpine meadows. In the dry meadow, the addition of nitrogen resulted in a 22-fold increase in N2O emissions, while in the wet meadow, we observed a 45-fold increase in N2O emission rates. CH4 uptake in the dry meadow was reduced 52% by fertilization; however, net CH4 production occurred in all the wet meadow plots and emission rates were not significantly affected by fertilization. Net nitrification rates in the dry meadow were higher in fertilized plots than in non-fertilized plots throughout the growing season; net mineralization...
We investigated the relationship between plant nitrogen limitation and water availability in dryland ecosystems. We tested the hypothesis that at lower levels of annual precipitation, aboveground net primary productivity (ANPP) is limited primarily by water whereas at higher levels of precipitation, it is limited primarily by nitrogen. Using a literature survey of fertilization experiments in arid, semi-arid, and subhumid ecosystems, we investigated the response of ANPP to nitrogen addition as a function of variation in precipitation across geographic gradients, as well as across year-to-year variation in precipitation within sites. We used four different indices to assess the degree of N limitation: (1) Absolute...
Knapweeds (Centaurea spp.) are among the most invasive of non-indigenous plant species that have colonized western North America over the last century. We conducted a 4-year experiment in a reconstructed grassland to test hypotheses related to the ability of grasslands to resist the invasion of diffuse knapweed (C. diffusa). We experimentally invaded C. diffusa and three native species into areas where we manipulated soil nitrogen (N) and phosphorus (P) availability and removed extant grasses to reduce competition. We evaluated the growth response of these species to these resources and competitive manipulations. Of the native species that were experimentally added, only one species, Ratibida pinnata (prairie coneflower),...
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This study evaluated sap flow of neotropical mangrove species subjected to background nutrient loading, and well as fertilization with either nitrogen or phosphorus, at Ding Darling National Wildlife Refuge (NWR). Data collections were made seasonally to model stand water use by mangrove forests as a metric of ecosystem stress through alteration of water use potential at the stand level. Data on leaf-scale water use efficiency, and data from a partial weather station deployed near study sites, were included for enabling model development and calculation of stand water use.
    map background search result map search result map Fluxes of nitrous oxide and methane from nitrogen-amended soils in a Colorado alpine ecosystem Revegetation Methods for High-Elevation Roadsides at Bryce Canyon National Park, Utah Sap flow, leaf water use efficiency, and partial weather station data to support stand water use modeling by nutrient treatment (N, P) for mangroves of Ding Darling NWR, Sanibel Island, Florida (2019-2020) Fluxes of nitrous oxide and methane from nitrogen-amended soils in a Colorado alpine ecosystem Sap flow, leaf water use efficiency, and partial weather station data to support stand water use modeling by nutrient treatment (N, P) for mangroves of Ding Darling NWR, Sanibel Island, Florida (2019-2020) Revegetation Methods for High-Elevation Roadsides at Bryce Canyon National Park, Utah