Showing papers by "Arvin R. Mosier published in 2007"

Carbon dioxide enrichment alters plant community structure and accelerates shrub growth in the shortgrass steppe

Abstract: A hypothesis has been advanced that the incursion of woody plants into world grasslands over the past two centuries has been driven in part by increasing carbon dioxide concentration, [CO(2)], in Earth's atmosphere. Unlike the warm season forage grasses they are displacing, woody plants have a photosynthetic metabolism and carbon allocation patterns that are responsive to CO(2), and many have tap roots that are more effective than grasses for reaching deep soil water stores that can be enhanced under elevated CO(2). However, this commonly cited hypothesis has little direct support from manipulative experimentation and competes with more traditional theories of shrub encroachment involving climate change, management, and fire. Here, we show that, although doubling [CO(2)] over the Colorado shortgrass steppe had little impact on plant species diversity, it resulted in an increasingly dissimilar plant community over the 5-year experiment compared with plots maintained at present-day [CO(2)]. Growth at the doubled [CO(2)] resulted in an approximately 40-fold increase in aboveground biomass and a 20-fold increase in plant cover of Artemisia frigida Willd, a common subshrub of some North American and Asian grasslands. This CO(2)-induced enhancement of plant growth, among the highest yet reported, provides evidence from a native grassland suggesting that rising atmospheric [CO(2)] may be contributing to the shrubland expansions of the past 200 years. Encroachment of shrubs into grasslands is an important problem facing rangeland managers and ranchers; this process replaces grasses, the preferred forage of domestic livestock, with species that are unsuitable for domestic livestock grazing.

Dinitrogen and N2O emissions in arable soils: Effect of tillage, N source and soil moisture☆

Abstract: A laboratory investigation was performed to compare the fluxes of dinitrogen (N2), N2O and carbon dioxide (CO2) from no-till (NT) and conventional till (CT) soils under the same water, mineral nitrogen and temperature status. Intact soil cores (0–10 cm) were incubated for 2 weeks at 251C at either 75% or 60% water-filled pore space (WFPS) with 15 N-labeled fertilizers (100 mg N kg � 1 soil). Gas and soil samples were collected at 1–4 day intervals during the incubation period. The N2O and CO2 fluxes were measured by a gas chromatography (GC) system while total N2 and N2O losses and their 15 N mole fractions in the soil mineral N pool were determined by a mass spectrometer. The daily accumulative fluxes of N2 and N2O were significantly affected by tillage, N source and soil moisture. We observed higher (Po0.05) fluxes of N2+N2O, N2O and CO2 from the NT soils than from the CT soils. Compared with the addition of nitrate (NO3 ), the addition of ammonium (NH4 ) enhanced the emissions of these N and C gases in the CT and NT soils, but the effect of NH4 on the N2 and/or N2O fluxes was evident only at 60% WFPS, indicating that nitrification and subsequent denitrification contributed largely to the gaseous N losses and N2O emission under the lower moisture condition. Total and fertilizer-induced emissions of N2 and/or N2O were higher (Po0.05) at 75% WFPS than with 60% WFPS, while CO2 fluxes were not influenced by the two moisture levels. These laboratory results indicate that there is greater potential for N2O loss from NT soils than CT soils. Avoiding wet soil conditions (460% WFPS) and applying a NO3 form of N fertilizer would reduce potential N2O emissions from arable soils.